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Massive molecular gas flows in the Abell 1664 brightest cluster galaxy
Abstract
We report ALMA Early Science CO(1-0) and CO(3-2) observations of the brightest cluster galaxy (BCG) in A1664. The BCG contains 1.1 × 1010M
☉ of molecular gas divided roughly equally between two distinct velocity systems: one from –250 to +250 km s–1 centered on the BCG's systemic velocity and a high-velocity system blueshifted by 570 km s–1 with respect to the systemic velocity. The BCG's systemic component shows a smooth velocity gradient across the BCG center, suggestive of rotation about the nucleus. However, the mass and velocity structure are highly asymmetric and there is little star formation coincident with a putative disk. It may be an inflow of gas that will settle into a disk over several 108 yr. The high-velocity system consists of two gas clumps, each ~2 kpc across, located to the north and southeast of the nucleus. Each has a line of sight velocity spread of 250-300 km s–1. The velocity of the gas in the high-velocity system increases toward the BCG center and may be a massive flow into the nucleus. However, the velocity gradient is not smooth. These structures are also coincident with low optical-ultraviolet surface brightness regions, which could indicate dust extinction associated with each clump. The structure is complex, making a clear interpretation difficult, but if the dusty, molecular gas lies predominantly in front of the BCG, the blueshifted velocities would indicate an outflow. Based on the energy requirements, such a massive outflow would most likely be driven by the active galactic nucleus. A merger origin is unlikely but cannot be ruled out.
... The star formation rate is estimated to be 14 M yr −1 in infrared (IR) or 4.3 M yr −1 in far-ultraviolet (FUV) (O'Dea et al. 2010). The BCG has a total molecular gas mass of 1.1±0.1 × 10 10 M (Russell et al. 2014). The molecular gas is also seen disturbed within 10 kpc of the core (Russell et al. 2014). ...
... The BCG has a total molecular gas mass of 1.1±0.1 × 10 10 M (Russell et al. 2014). The molecular gas is also seen disturbed within 10 kpc of the core (Russell et al. 2014). The CO(1-0) and CO(3-2) lines are well resolved into two Gaussian components with a velocity difference of ∼590 km s −1 . ...
... The shift in velocity is then seen in spatial coincidence with cold fronts (Sanders et al. 2020). In A1664, the molecular gas system in the centre is divided in two roughly equal clumps with a velocity separation of 600 km s −1 (Russell et al. 2014). The blueshifted component is seen at a velocity of 571 ± 7 km s −1 from CO (3-2) in our line of sight, with a full width at half-maximum of 190 ± 20 km s −1 . ...
We present the analysis of XMM-Newton observations of two X-ray luminous cool core clusters, RXCJ1504.1-0248 and Abell 1664. The Reflection Grating Spectrometer reveals a radiative cooling rate of $180\pm 40\, \rm M_{\odot }\rm \, yr^{-1}$ and $34\pm 6\, \rm M_{\odot }\rm \, yr^{-1}$ in RXCJ1504.1-0248 and Abell 1664 for gas above 0.7 keV, respectively. These cooling rates are higher than the star formation rates observed in the clusters, and support simultaneous star formation and molecular gas mass growth on a timescale of 3× 108 yr or longer. At these rates, the energy of the X-ray cooling gas is inadequate to power the observed UV/optical line-emitting nebulae, which suggests additional strong heating. No significant residual cooling is detected below 0.7 keV in RXCJ1504.1-0248. By simultaneously fitting the first and second order spectra, we place an upper limit on turbulent velocity of 300 km $\rm s^{-1}$ at 90 per cent confidence level for the soft X-ray emitting gas in both clusters. The turbulent energy density is considered to be less than 8.9 and 27 per cent of the thermal energy density in RXCJ1504.1-0248 and Abell 1664, respectively. This means it is insufficient for AGN heating to fully propagate throughout the cool core via turbulence. We find the cool X-ray component of Abell 1664 (∼0.8 keV) is blueshifted from the systemic velocity by 750$^{+800}_{-280}$ km $\rm s^{-1}$. This is consistent with one component of the molecular gas in the core and suggests a similar dynamical structure for the two phases. We find that an intrinsic absorption model allows the cooling rate to increase to $520\pm 30\, \rm M_{\odot }\rm \, yr^{-1}$ in RXCJ1504.1-0248.
... The star formation rate is estimated to be 14 M yr −1 in IR or 4.3 M yr −1 in FUV (O'Dea et al. 2010). The BCG has a total molecular gas mass of 1.1±0.1× 10 10 M (Russell et al. 2014). The molecular gas is also seen disturbed within 10 kpc of the core (Russell et al. 2014). ...
... The BCG has a total molecular gas mass of 1.1±0.1× 10 10 M (Russell et al. 2014). The molecular gas is also seen disturbed within 10 kpc of the core (Russell et al. 2014). The CO(1-0) and CO(3-2) lines are well resolved into two Gaussian components with a velocity difference of ∼590 km s −1 . ...
... In A1664, the molecular gas system in the centre is divided in 2 roughly equal clumps with a velocity separation of 600 km s −1 (Russell et al. 2014). The blueshifted component is seen at a velocity of 571±7 km s −1 from CO(3-2) in our line-of-sight, with a FWHM of 190±20 km s −1 . ...
We present the analysis of XMM-Newton observations of two X-ray luminous cool core clusters, RXCJ1504.1-0248 and Abell 1664. The Reflection Grating Spectrometer reveals a radiative cooling rate of $180\pm 40\, \rm M_{\odot}\rm\,yr^{-1}$ and $34\pm 6\, \rm M_{\odot}\rm\,yr^{-1}$ in RXCJ1504.1-0248 and Abell 1664 for gas above 0.7 keV, respectively. These cooling rates are higher than the star formation rates observed in the clusters, and support simultaneous star formation and molecular gas mass growth on a timescale of 3$\times 10^8$ yr or longer. At these rates, the energy of the X-ray cooling gas is inadequate to power the observed UV/optical line-emitting nebulae, which suggests additional strong heating. No significant residual cooling is detected below 0.7 keV in RXCJ1504.1-0248. By simultaneously fitting the first and second order spectra, we place an upper limit on turbulent velocity of 300 km$\rm s^{-1}$ at 90 per cent confidence level for the soft X-ray emitting gas in both clusters. The turbulent energy density is considered to be less than 8.9 and 27 per cent of the thermal energy density in RXCJ1504.1-0248 and Abell 1664, respectively. This means it is insufficient for AGN heating to fully propagate throughout the cool core via turbulence. We find the cool X-ray component of Abell 1664 ($\sim$0.8 keV) is blueshifted from the systemic velocity by 750$^{+800}_{-280}$ km$\rm s^{-1}$. This is consistent with one component of the molecular gas in the core and suggests a similar dynamical structure for the two phases. We find that an intrinsic absorption model allows the cooling rate to increase to $520\pm 30\, \rm M_{\odot}\rm\,yr^{-1}$ in RXCJ1504.1-0248.
... The rotationally supported disks that would be expected from the long-lived accumulation of molecular clouds in the galactic center are rare (Hamer et al. 2014;Russell et al. 2019). Instead, billions of solar masses of cold gas are situated in kiloparsecscale filaments that trail X-ray cavities (e.g., Salomé et al. 2006Salomé et al. , 2008Lim & Ao 2008;Lim et al. 2012;McDonald et al. 2012a;McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Russell et al. , 2017aRussell et al. , 2017bVantyghem et al. 2016Vantyghem et al. , 2018Vantyghem et al. , 2019. The detection of redshifted absorption lines indicates that some of this gas rains back onto the central galaxy in a circulation flow (David et al. 2014;Tremblay et al. 2016Tremblay et al. , 2018Rose et al. 2019bRose et al. , 2019aRose et al. , 2020. ...
... However, the molecular gas in BCGs is often distributed over much larger spatial scales than in ULIRGs, where the gas is confined to the central kiloparsec. Despite their elevated star formation rates (SFRs), BCGs still lie on the Kennicutt-Schmidt relation (Kennicutt 1998; Kennicutt & Evans 2012) alongside normal galaxies (see, e.g., McNamara et al. 2014;Russell et al. 2014;Vantyghem et al. 2018). ...
... Previous single-dish and interferometric radio observations of Zw 3146 with the IRAM-30 m telescope and Owens Valley Radio Telescope (OVRO) yielded CO(1−0) integrated fluxes of 5.2 ± 1.2 Jy km s −1 and 5.7 ± 0.9 Jy km s −1 , respectively (Edge 2001;Edge & Frayer 2003). Our ALMA observation recovers 50% of this flux; a similar fraction to that of other BCGs (e.g., David et al. 2014;Russell et al. 2014;McNamara et al. 2014;Vantyghem et al. 2018). The line emission in the OVRO observations, which recovers all of the single-dish flux, is unresolved by the 6 7″ × 4 7 beam. ...
jats:title>Abstract We present a recent Atacama Large Millimeter/submillimeter Array observation of the CO(1−0) line emission in the central galaxy of the Zw 3146 galaxy cluster ( z = 0.2906). We also present updated X-ray cavity measurements from archival Chandra observations. The 5 × 10 10 M ⊙ supply of molecular gas, which is confined to the central 4 kpc, is marginally resolved into three extensions that are reminiscent of the filaments observed in similar systems. No velocity structure that would be indicative of ordered motion is observed. The three molecular extensions all trail X-ray cavities, and are potentially formed from the condensation of intracluster gas lifted in the wakes of the rising bubbles. Many cycles of feedback would be required to account for the entire molecular gas reservoir. The molecular gas and continuum source are mutually offset by 2.6 kpc, with no detected line emission coincident with the continuum source. It is the molecular gas, not the continuum source, that lies at the gravitational center of the brightest cluster galaxy. As the brightest cluster galaxy contains possible tidal features, the displaced continuum source may correspond to the nucleus of a merging galaxy. We also discuss the possibility that a gravitational wave recoil following a black hole merger may account for the displacement.</jats:p
... The profile falls below 30 keV cm 2 at a radius of 46 kpc (20″), a threshold below which Rafferty et al. (2008) find a higher occurrence rate of multiphase gas and ongoing star formation. Indeed, the ALMA observations of molecular gas in this system by Russell et al. (2014) support this scenario. Where this molecular gas might come from is discussed in Section 4. The entropy profile reaches S=21.1±9.3 ...
... At 6.0 keV, we essentially see a screen of hotter gas in projection, but concentrated especially in the X-ray bar at 3.0 keV. At 1.5 keV, the gas is still concentrated along the bar but appears to be most abundant slightly north of the core, possibly toward the molecular gas reservoir centered on the BCG from Russell et al. (2014). This region is slightly enhanced still in the 0.75 keV map, albeit more faintly as these maps have been normalized to the same intensity scale. ...
... The contours from the molecular CO emission measured by ALMA are overlaid and are found just behind or inside the putative eastern cavity. The systemic possible "disk" component and the high-velocity system are described in detail inRussell et al. (2014).Right: HST WFPC2 F606W image of A1664 for comparison, from O'Dea et al. (2010), with JVLA 1.8 GHz contours overlaid (courtesy of A. C. Edge).the standard deviation of all eight surface brightness measurements then dividing by the square root of the number of measurements (i.e., 8). The surface brightness of P1 (P2) is 1.36 0. ...
We present new, deep (245 ks) Chandra observations of the galaxy cluster Abell 1664 (z = 0.1283). These images reveal rich structure, including elongation and accompanying compressions of the X-ray isophotes in the NE–SW direction, suggesting that the hot gas is sloshing in the gravitational potential. This sloshing has resulted in cold fronts, at distances of 50, 110, and 325 kpc from the cluster center. Our results indicate that the core of A1664 is highly disturbed, as the global metallicity and cooling time flatten at small radii, implying mixing on a range of scales. The central active galactic nucleus (AGN) appears to have recently undergone a mechanical outburst, as evidenced by our detection of cavities. These cavities are the X-ray manifestations of radio bubbles inflated by the AGN and may explain the motion of cold molecular CO clouds previously observed with the Atacama Large Millimeter Array (ALMA). The estimated mechanical power of the AGN, using the minimum energy required to inflate the cavities as a proxy, is erg s⁻¹, which may be enough to drive the molecular gas flows, and offset the cooling luminosity of the intracluster medium, at erg s⁻¹. This mechanical power is orders of magnitude higher than the measured upper limit on the X-ray luminosity of the central AGN, suggesting that its black hole may be extremely massive and/or radiatively inefficient. We map temperature variations on the same spatial scale as the molecular gas and find that the most rapidly cooling gas is mostly coincident with the molecular gas reservoir centered on the brightest cluster galaxy's systemic velocity observed with ALMA and may be fueling cold accretion onto the central black hole.
... The density contrast between hot (∼10 7 K) plasma and cold (∼10 K) molecular gas is nearly a million times greater than that between air and granite. So while one might naturally expect that the working surface of a jet can drive sound waves and shocks into the tenuous X-ray atmosphere, it is more difficult to explain the growing literature reporting observations of massive atomic and molecular outflows apparently entrained by jets (e.g., Morganti et al. 2005Morganti et al. , 2013Alatalo et al. 2011Alatalo et al. , 2015Cicone et al. 2014Cicone et al. , 2018Dasyra et al. 2015) or uplifted in the wakes of the buoyant hot bubbles they inflate (e.g., McNamara et al. 2014McNamara et al. , 2016Russell et al. 2014Russell et al. , 2016Russell et al. , 2017aRussell et al. , 2017b. One might instead expect molecular nebulae to act like seawalls, damping turbulence, breaking waves in the hotter phases of the Interstellar Medium (ISM), and redirecting jets. ...
... This is not guaranteed, as warm ionized gas can be present without cold molecular gas (e.g., Simionescu et al. 2018). We do note that most ALMA observations of CC BCGs published thus far generally show molecular filaments cospatial with warm ionized counterparts Russell et al. 2014Russell et al. , 2016Russell et al. , 2017aRussell et al. , 2017bVantyghem et al. 2016). This has been known long prior to the first ALMA observations, too (see, e.g., the single-dish observations of the Perseus filaments by Lim et al. 2008;Salomé et al. 2011). ...
... The kinematics of the molecular nebula can therefore be considered rather slow, unless most gas motions are contained in the plane of the sky. This is unlikely, given several recent papers reporting similarly slow cold gas motions in CC BCGs Russell et al. 2014Russell et al. , 2016Russell et al. , 2017aRussell et al. , 2017bVantyghem et al. 2016). The overall picture for A2597, then, is that of a slow, churning "mist" of cold gas, drifting in the turbulent velocity field of the hot atmosphere, with complex inward and outward streaming motions. ...
We present Atacama Large Millimeter/submillimeter Array and Multi-Unit Spectroscopic Explorer observations of the brightest cluster galaxy in Abell 2597, a nearby (z = 0.0821) cool core cluster of galaxies. The data map the kinematics of a three billion solar mass filamentary nebula that spans the innermost 30 kpc of the galaxy's core. Its warm ionized and cold molecular components are both cospatial and comoving, consistent with the hypothesis that the optical nebula traces the warm envelopes of many cold molecular clouds that drift in the velocity field of the hot X-ray atmosphere. The clouds are not in dynamical equilibrium, and instead show evidence for inflow toward the central supermassive black hole, outflow along the jets it launches, and uplift by the buoyant hot bubbles those jets inflate. The entire scenario is therefore consistent with a galaxy-spanning "fountain," wherein cold gas clouds drain into the black hole accretion reservoir, powering jets and bubbles that uplift a cooling plume of low-entropy multiphase gas, which may stimulate additional cooling and accretion as part of a self-regulating feedback loop. All velocities are below the escape speed from the galaxy, and so these clouds should rain back toward the galaxy center from which they came, keeping the fountain long lived. The data are consistent with major predictions of chaotic cold accretion, precipitation, and stimulated feedback models, and may trace processes fundamental to galaxy evolution at effectively all mass scales. © 2018. The American Astronomical Society. All rights reserved.
... Detailed observations of the molecular gas content are available for only a dozen systems or so. These studies have revealed molecular gas filaments trailing behind buoyantly rising X-ray cavities and interacting with radio lobes (McNamara et al. 2014 ;Russell et al. 2014Russell et al. , 2016Russell et al. , 2017bVantyghem et al. 2016Vantyghem et al. , 2018. These spatial correlations indicate that radio AGNs are disrupting and perhaps expelling molecular gas from the central galaxies. ...
... Their position-velocity (PV) diagrams do not show the characteristic 'S'-shaped curve that represents rotation (see Fig. A2 ). Some of the molecular gas in A1664 may be forming a disc of molecular gas in the centre (Russell et al. 2014 ). Similarly, the circumnuclear gas reservoir in phoenix has a smooth velocity gradient from −200 to 200 km s −1 suggestive of a disc (Russell et al. 2017b ). ...
Molecular gas flows are analyzed in 14 cluster galaxies (BCGs) centered in cooling hot atmospheres. The BCGs contain $10^{9}-10^{11}~\rm M_\odot$ of molecular gas, much of which is being moved by radio jets and lobes. The molecular flows and radio jet powers are compared to molecular outflows in 45 active galaxies within z < 0.2. We seek to understand the relative efficacy of radio, quasar, and starburst feedback over a range of active galaxy types. Molecular flows powered by radio feedback in BCGs are ∼10–1000 times larger in extent compared to contemporary galaxies hosting quasar nuclei and starbursts. Radio feedback yields lower flow velocities but higher momenta compared to quasar nuclei, as the molecular gas flows in BCGs are usually ∼10–100 times more massive. The product of the molecular gas mass and lifting altitude divided by the AGN or starburst power — a parameter referred to as the lifting factor—exceeds starbursts and quasar nuclei by two to three orders of magnitude, respectively. When active, radio feedback is generally more effective at lifting gas in galaxies compared to quasars and starburst winds. The kinetic energy flux of molecular clouds generally lies below and often substantially below a few percent of the driving power. We find tentatively that star formation is suppressed in BCGs relative to other active galaxies, perhaps because these systems rarely form molecular disks that are more impervious to feedback and are better able to promote star formation.
... Detailed observations of the molecular gas content are available for only a dozen systems or so. These studies have revealed molecular gas filaments trailing behind buoyantly rising X-ray cavities and interacting with radio lobes (McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Russell et al. , 2017bVantyghem et al. 2016Vantyghem et al. , 2018. These spatial correlations indicate that radio AGN are disrupting and perhaps expelling molecular gas from the central galaxies. ...
... Their position-velocity (PV) diagrams do not show the characteristic 'S'shaped curve that represents rotation (see Fig. A2). Some of the molecular gas in A1664 may be forming a disk of molecular gas in the centre (Russell et al. 2014). Similarly, the circumnuclear gas reservoir in phoenix has a smooth velocity gradient from −200 to 200 km s −1 suggestive of a disk (Russell et al. 2017b). ...
Molecular gas flows are analyzed in 14 cluster galaxies (BCGs) centered in cooling hot atmospheres. The BCGs contain $10^{9}-10^{11}~\rm M_\odot$ of molecular gas, much of which is being moved by radio jets and lobes. The molecular flows and radio jet powers are compared to molecular outflows in 45 active galaxies within $z<0.2$. We seek to understand the relative efficacy of radio, quasar, and starburst feedback over a range of active galaxy types. Molecular flows powered by radio feedback in BCGs are $\sim$10--1000 times larger in extent compared to contemporary galaxies hosting quasar nuclei and starbursts. Radio feedback yields lower flow velocities but higher momenta compared to quasar nuclei, as the molecular gas flows in BCGs are usually $\sim$10--100 times more massive. The product of the molecular gas mass and lifting altitude divided by the AGN or starburst power -- a parameter referred to as the lifting factor -- exceeds starbursts and quasar nuclei by two to three orders of magnitude, respectively. When active, radio feedback is generally more effective at lifting gas in galaxies compared to quasars and starburst winds. The kinetic energy flux of molecular clouds generally lies below and often substantially below a few percent of the driving power. We find tentatively that star formation is suppressed in BCGs relative to other active galaxies, perhaps because these systems rarely form molecular disks that are more impervious to feedback and are better able to promote star formation.
... In addition to the hot X-ray gas, much cooler gas has been discovered in the central galaxies in the core of galaxy clusters. For example, massive molecular gas ( 10 9 M ) has been detected, although the mass is much smaller than the prediction of a classical cooling flow model (Edge 2001;Salomé & Combes 2003;David et al. 2014;McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Tremblay et al. 2016;Vantyghem et al. 2016). Nebular emission associated with warm gas has also been observed (Heckman et al. 1989;Crawford et al. 1999;McDonald et al. 2010;Tremblay et al. 2015). ...
... In addition to the hot X-ray gas, much cooler gas has been discovered in the central galaxies in the core of galaxy clusters. For example, massive molecular gas ( 10 9 M ) has been detected, although the mass is much smaller than the prediction of a classical cooling flow model (Edge 2001;Salomé & Combes 2003;David et al. 2014;McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Tremblay et al. 2016;Vantyghem et al. 2016). Nebular emission associated with warm gas has also been observed (Heckman et al. 1989;Crawford et al. 1999;McDonald et al. 2010;Tremblay et al. 2015). ...
Massive molecular gas has been discovered in giant elliptical galaxies at the centers of galaxy clusters. To reveal its role in AGN feedback in those galaxies, we construct a semi-analytic model of gas circulation. This model especially focuses on the massive molecular gas (interstellar cold gas on a scale of ~10 kpc) and the circumnuclear disk (~< 0.5 kpc). We consider the destruction of the interstellar cold gas by star formation and the gravitational instability for the circumnuclear disk. Our model can reproduce the basic properties of the interstellar cold gas and the circumnuclear disk such as their masses. We also find that the circumnuclear disk tends to stay at the boundary between stable and unstable states. This works as an 'adjusting valve' that regulates mass accretion toward the supermassive black hole. On the other hand, the interstellar cold gas serves as a 'fuel tank' in the AGN feedback. Even if the cooling of the galactic hot gas is prevented, the interstellar cold gas can sustain the AGN activities for ~> 0.5 Gyr. We also confirm that the small entropy of the hot gas (~< 30 keV cm^2) or the short cooling time (~< 1 Gyr) is a critical condition for the existence of the massive molecular gas in the galaxy. The dissipation time of the interstellar cold gas may be related to the critical cooling time.
... Atacama Large Millimetre Array (ALMA) has observed nearly a dozen central galaxies in groups and clusters (David et al. 2014;McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Russell et al. , 2017aRussell et al. , 2017bTremblay et al. 2016;Vantyghem et al. 2016Vantyghem et al. , 2017Simionescu et al. 2018). ALMA images show that much of the molecular gas lies outside of the nucleus in most systems. ...
... Other studies have focused on the relationship between molecular gas and the stellar content and their dynamics (Young et al. 2008;Emsellem et al. 2001Emsellem et al. , 2011, or the relationship between atmospheric properties, the stars, and the central black hole (Ma et al. 2014). This study extends our work on central galaxies in clusters, whose molecular gas is closely tied to their atmospheres (Edge et al. 2002;David et al. 2014David et al. , 2017McNamara et al. 2014;Russell et al. 2014Russell et al. , 2015Russell et al. , 2017aTremblay et al. 2016;Vantyghem et al. 2017Vantyghem et al. , 2018Pulido et al. 2018), to lower-mass atmospheres and their parent halos. Table 1 lists the sample, including target name, coordinates, Chandra observational ID, cleaned exposure time, morphology, galaxy classification, redshift, angular and luminosity distance, foreground hydrogen column density taken from Dickey & Lockman (1990), and radio flux. ...
We analyze Chandra observations of the hot atmospheres of 40 early spiral and elliptical galaxies. Using new temperature, density, cooling time, and mass profiles, we explore relationships between their hot atmospheres and cold molecular gas. Molecular gas mass correlates with atmospheric gas mass and density over four decades from central galaxies in clusters to normal giant ellipticals and early spirals. The mass and density relations follow power laws: Mmol ∝ MX1.4 ± 0.1 and Mmol ∝ ne1.8 ± 0.3, respectively, at 10 kpc. The ratio of molecular gas to atmospheric gas within a 10 kpc radius lies between 3% and 10% for early-type galaxies and between 3% and 50% for central galaxies in clusters. Early-type galaxies have detectable levels of molecular gas when their atmospheric cooling times fall below ∼1 Gyr at a radius of 10 kpc. A similar trend is found in central cluster galaxies. We find no relationship between the ratio of the cooling time to free-fall time, t c/t ff, and the presence or absence of molecular clouds in early-type galaxies. The data are consistent with much of the molecular gas in early-type galaxies having condensed from their hot atmospheres. © 2019. The American Astronomical Society. All rights reserved.
... Recent observations of BCGs with the Atacama Large Millimeter Array (ALMA) have found evidence of CO molecular gas tracing AGN jet outflows, providing observational support for the notion that molecular gas reservoirs in these systems are fueled by >10 7 K gas that condenses as it is being uplifted by the jets Russell et al. 2014Russell et al. , 2017aRussell et al. , 2017b. CO has also been observed in absorption along the line of sight to the AGNs of BCGs, providing direct evidence for the accretion of cold gas onto the AGN (Tremblay et al. 2016Rose et al. 2019). ...
... Russell et al. 2014).Hlavacek- Larrondo et al. (2012) detect probable cavities in the core of MACS 1931; these detected features are found to the east and west of the BCG, as opposed to the approximately north-south orientation of the extended molecular gas. ...
We present new Atacama Large Millimeter Array observations of the molecular gas and far-infrared continuum around the brightest cluster galaxy (BCG) in the cool-core cluster MACS 1931.8-2635. Our observations reveal (1.9 ± 0.3) × 10^(10) M⊙ of molecular gas, on par with the largest known reservoirs of cold gas in a cluster core. We detect CO(1−0), CO(3−2), and CO(4−3) emission from both diffuse and compact molecular gas components that extend from the BCG center out to ~30 kpc to the northwest, tracing the UV knots and Hα filaments observed by the Hubble Space Telescope. Due to the lack of morphological symmetry, we hypothesize that the ~300 km s−1 velocity of the CO in the tail is not due to concurrent uplift by active galactic nucleus (AGN) jets; rather, we may be observing the aftermath of a recent AGN outburst. The CO spectral line energy distribution suggests that molecular gas excitation is influenced by processes related to both star formation and recent AGN feedback. Continuum emission in Bands 6 and 7 arises from dust and is spatially coincident with young stars and nebular emission observed in the UV and optical. We constrain the temperature of several dust clumps to be ≾10 K, which is too cold to be directly interacting with the surrounding ~4.8 keV intracluster medium (ICM). The cold dust population extends beyond the observed CO emission and must either be protected from interacting with the ICM or be surrounded by local volumes of ICM that are several keV colder than observed by Chandra.
... For many hydrodynamical simulations, AGN activity remains the favoured dominant candidate for feedback (e.g., McCarthy et al. 2016;Schaye et al. 2015;Vogelsberger et al. 2014), although some studies are moving towards closer examination of external baryonic processes such as ram-pressure stripping and shock heating (e.g., Steinhauser et al. 2016). Indeed, high rates of star formation (10 1 −10 2 M yr −1 ), have been detected in some BCGs within clusters hosting cool-cores (e.g., O'Dea et al. 2008;Edge 2001) as well as enhanced AGN activity (e.g., Burns 1990) and giant molecular gas outflows (e.g., Russell et al. 2014). However, mass deposition rates may still be too slow to reproduce the mass range of BCGs through in-situ star formation alone (e.g., Peterson & Fabian 2006), alongside strong cool-core systems being relatively rare at higher redshifts where observations suggest BCGs gain the bulk of their mass Collins et al. 2009). ...
... Burns 1990, Crawford et al. 1999, the feedback from which are thought to be capable of heating the ICM (e.g. McNamara et al. 2014, Russell et al. 2014). ...
We present a sample of 329 low to intermediate redshift ($0.05 < z < 0.3$) brightest cluster galaxies (BCGs) in X-ray selected clusters from the SPectroscopic IDentification of eRosita Sources (SPIDERS) survey, a spectroscopic survey within Sloan Digital Sky Survey-IV (SDSS-IV). We define our BCGs by simultaneous consideration of legacy X-ray data from ROSAT, maximum likelihood outputs from an optical cluster-finder algorithm and visual inspection. Using SDSS imaging data, we fit S\'ersic profiles to our BCGs in three bands (\textit{g}, \textit{r}, \textit{i}) with \textsc{SIGMA}, a \textsc{GALFIT}-based software wrapper. We examine the reliability of our fits by running our pipeline on ${\sim}10^{4}$ psf-convolved model profiles injected into 8 random cluster fields, we then use the results of this analysis to create a robust subsample of 198 BCGs. We outline three cluster properties of interest: overall cluster X-ray luminosity ($L_{X}$), cluster richness as estimated by \textsc{redMaPPer} ($ \lambda $) and cluster halo mass ($M_{200}$), which is estimated via velocity dispersion. In general, there are significant correlations with BCG stellar mass between all three environmental properties, but no significant trends arise with either S\'ersic index or effective radius. There is no major environmental dependence on the strength of the relation between effective radius and BCG stellar mass. Stellar mass therefore arises as the most important factor governing BCG morphology. Our results indicate that our sample consists of a large number of relaxed, mature clusters containing broadly homogeneous BCGs up to $z \sim 0.3$, suggesting that there is little evidence for much ongoing structural evolution for BCGs in these systems.
... Russell et al. 2017;Olivares et al. 2019;Jimenez-Gallardo et al. 2021;North et al. 2021). Cold molecular gas is also observed with radio observations of CO lines surrounding the BCG at radii of 50 kpc or so, as a result of inflows (Edge 2001;Salomé & Combes 2004;North et al. 2021), and most notably up to within 10 kpc of the central BCG with ALMA (McNamara et al. 2014;Russell et al. 2014;Fogarty et al. 2019). This inflow is thought to increase the growth efficiency and the magnitude of the feedback from the SMBH (DeGraf et al. 2016), with important implications for the morphology of the gas around the central object. ...
In galaxy clusters, the hot intracluster medium (ICM) can develop a striking multi-phase structure around the brightest cluster galaxy. Much work has been done on understanding the origin of this central nebula, but less work has studied its eventual fate after the originally filamentary structure is broken into individual cold clumps. In this paper we perform a suite of 30 (magneto-)hydrodynamical simulations of kpc-scale cold clouds with typical parameters as found by galaxy cluster simulations, to understand whether clouds are mixed back into the hot ICM or can persist. We investigate the effects of radiative cooling, small-scale heating, magnetic fields, and (anisotropic) thermal conduction on the long-term evolution of clouds. We find that filament fragments cool on timescales shorter than the crushing timescale, fall out of pressure equilibrium with the hot medium, and shatter, forming smaller clumplets. These act as nucleation sites for further condensation, and mixing via Kelvin-Helmholtz instability, causing cold gas mass to double within 75 Myr. Cloud growth depends on density, as well as on local heating processes, which determine whether clouds undergo ablation- or shattering-driven evolution. Magnetic fields slow down but don’t prevent cloud growth, with the evolution of both cold and warm phase sensitive to the field topology. Counter-intuitively, anisotropic thermal conduction increases the cold gas growth rate compared to non-conductive clouds, leading to larger amounts of warm phase as well. We conclude that dense clumps on scales of 500 pc or more cannot be ignored when studying the long-term cooling flow evolution of galaxy clusters.
... Russell et al. 2017;Olivares et al. 2019;Jimenez-Gallardo et al. 2021;North et al. 2021). Cold molecular gas is also observed with radio observations of CO lines surrounding the BCG at radii of 50 kpc or so, as a result of inflows (Edge 2001;Salomé & Combes 2004;North et al. 2021), and most notably up to within 10 kpc of the central BCG with ALMA (McNamara et al. 2014;Russell et al. 2014;Fogarty et al. 2019). This inflow is thought to increase the growth efficiency and the magnitude of the feedback from the SMBH (DeGraf et al. 2016), with important implications for the morphology of the gas around the central object. ...
In galaxy clusters, the hot intracluster medium (ICM) can develop a striking multi-phase structure around the brightest cluster galaxy. Much work has been done on understanding the origin of this central nebula, but less work has studied its eventual fate after the originally filamentary structure is broken into individual cold clumps. In this paper we perform a suite of 30 (magneto-)hydrodynamical simulations of kpc-scale cold clouds with typical parameters as found by galaxy cluster simulations, to understand whether clouds are mixed back into the hot ICM or can persist. We investigate the effects of radiative cooling, small-scale heating, magnetic fields, and (anisotropic) thermal conduction on the long-term evolution of clouds. We find that filament fragments cool on timescales shorter than the crushing timescale, fall out of pressure equilibrium with the hot medium, and shatter, forming smaller clumplets. These act as nucleation sites for further condensation, and mixing via Kelvin-Helmholtz instability, causing cold gas mass to double within 75 Myr. Cloud growth depends on density, as well as on local heating processes, which determine whether clouds undergo ablation- or shattering-driven evolution. Magnetic fields slow down but don't prevent cloud growth, with the evolution of both cold and warm phase sensitive to the field topology. Counter-intuitively, anisotropic thermal conduction increases the cold gas growth rate compared to non-conductive clouds, leading to larger amounts of warm phase as well. We conclude that dense clumps on scales of $500$ pc or more cannot be ignored when studying the long-term cooling flow evolution of galaxy clusters.
... In addition to the hot X-ray gas, much cooler gas has been discovered in the central galaxies in the core of galaxy clusters. For example, massive molecular gas clouds (10 9 M e ) have been detected, although the mass is much smaller than the prediction of a classical cooling flow model (Edge 2001;Salomé and Combes 2003;David et al. 2014;McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Tremblay et al. 2016;Vantyghem et al. 2016). Nebular emission associated with warm gas has also been observed (Heckman et al. 1989;Crawford et al. 1999;McDonald et al. 2010;Tremblay et al. 2015). ...
Massive molecular gas has been discovered in giant elliptical galaxies at the centers of galaxy clusters. To reveal its role in active galactic nucleus (AGN) feedback in those galaxies, we construct a semianalytical model of gas circulation. This model especially focuses on the massive molecular gas (interstellar cold gas on a scale of ∼10 kpc) and the circumnuclear disk (≲0.5 kpc). We consider the destruction of the interstellar cold gas by star formation and the gravitational instability for the circumnuclear disk. Our model can reproduce the basic properties of the interstellar cold gas and the circumnuclear disk, such as their masses. We also find that the circumnuclear disk tends to stay at the boundary between stable and unstable states. This works as an “adjusting valve” that regulates mass accretion toward the supermassive black hole. On the other hand, the interstellar cold gas serves as a “fuel tank” in the AGN feedback. Even if the cooling of the galactic hot gas is prevented, the interstellar cold gas can sustain the AGN activity for ≳0.5 Gyr. We also confirm that the small entropy of hot gas (≲30 keV cm ² ) or the short cooling time (≲1 Gyr) is a critical condition for the existence of massive amounts of molecular gas in the galaxy. The dissipation time of the interstellar cold gas may be related to the critical cooling time. The galaxy behavior is described by a simple relation among the disk stability, the cloud dissipation time, and the gas cooling rate.
... A leap forward in understanding the fueling of supermassive black holes is brought by molecular gas detected at centers of strong cooling systems (Edge 2001). High-resolution submillimeter observations, particularly with ALMA, reveal that such molecular clouds have a surprisingly low velocity and reside preferentially in the wake of buoyant bubbles (Russell et al. 2014(Russell et al. , 2017Vantyghem et al. 2016). McNamara et al. (2016) therefore proposed that low-entropy gas lifted by rising bubbles becomes thermally unstable and condenses into molecular gas, which could in turn fuel the AGN, dubbed as "stimulated feedback." ...
The M49 group, residing outside the virial radius of the Virgo cluster, is falling onto the cluster from the south. We report results from deep XMM-Newton mosaic observations of M49. Its hot gas temperature is 0.8 keV at the group center and rises to 1.5 keV beyond the brightest group galaxy (BGG). The group gas extends to radii of ∼300 kpc to the north and south. The observations reveal a cold front ∼20 kpc north of the BGG center and an X-ray-bright stripped tail 70 kpc long and 10 kpc wide to the southwest of the BGG. We argue that the atmosphere of the infalling group was slowed by its encounter with the Virgo cluster gas, causing the BGG to move forward subsonically relative to the group gas. We measure declining temperature and metallicity gradients along the stripped tail. The tail gas can be traced back to the cooler and enriched gas uplifted from the BGG center by buoyant bubbles, implying that active galactic nucleus outbursts may have intensified the stripping process. We extrapolate to a virial radius of 740 kpc and derive a virial mass of 4.6 × 10 ¹³ M ⊙ for the M49 group. Its group atmosphere appears truncated and deficient when compared with isolated galaxy groups of similar temperatures. If M49 is on its first infall to Virgo, the infall region of a cluster could have profound impacts on galaxies and groups that are being accreted onto galaxy clusters. Alternatively, M49 may have already passed through Virgo once.
... The deposition of cool gas in BCGs owing to a residual cooling of their surrounding intracluster gas -hereafter a residual cooling flow, no matter how this cooling actually occurs -differs from any cool gas accreted through wet mergers with cluster member galaxies in several important ways: (i) the mass of cool gas in BCGs can be, as appears to be observed, substantially higher than what would be expected from mergers with cluster member galaxies that have had much of their gas removed by ram-pressure stripping; (ii) the spatial distribution of cool gas can be highly extended owing to an interplay with the AGN jets, rather than dissipatively accumulating at the centers of BCGs as would be expected in wet mergers; and (iii) the continuous deposition (albeit perhaps at a time-varying rate) and therefore replenishment of cool gas can sustain star formation at a high rate over an indefinite period, by contrast with wet mergers whereby gas is accreted in a single episode to spark a brief period of star formation. Consistent with these expectations, the optical emission-line nebulae of BCGs can, and indeed quite often, extend over several 10 kpc if not over 100 kpc (e.g., Lynds 1970;Conselice et al. 2001;Tremblay et al. 2015), as do their molecular gas as traced in CO (Salomé et al. 2011;McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Vantyghem et al. 2016;Russell et al. 2017a,b) and star formation as traced in UV emission (Tremblay et al. 2015;Donahue et al. 2015). In the best studied example, NGC 1275 at the center of the Perseus cluster, its filamentary optical emissionline nebula spans ∼140 kpc (Lynds 1970;Conselice et al. 2001) compared with an effective (optical) radius for this galaxy of ∼25 kpc (Smith et al. 1990). ...
Brightest cluster galaxies (BCGs), particularly those at the centers of cool-core clusters, can exhibit star formation over spatial extents of up to $\gtrsim$100\,kpc at inferred rates of up to $\gtrsim100\rm\,M_\sun\,yr^{-1}$. Is their star formation also extended over time, as might be expected if fuelled by cooling of the surrounding hot intracluster gas -- a residual cooling flow -- as demonstrated hitherto only for the BCG in the Perseus cluster? Here, to infer the formation history of relatively young stars in the BCG of MACS\,J0329.7$-$0211, we fit model single-stellar-populations to the spectral energy distributions (spanning near-UV to near-IR) measured along different sightlines towards its young stellar population. Employing a Markov Chain Monte Carlo method, we show that star formation in this BCG has persisted at a relatively constant rate of $\sim2{\rm\,M_\sun\,yr^{-1}}$ (factors of 10--40 below the rates previously inferred using simpler methods and/or ad hoc assumptions) over the past $\sim$400\,Myr, beyond which any star formation falls below the observational detection threshold. Such persistent star formation from a residual cooling flow can contribute up to $\sim$10\% of the original stellar mass of this BCG if its progenitor was among the most massive red nuggets known at $z\sim$2 having masses of $\sim1\times10^{11}\rm\,M_\sun$, but only a few percent of its overall growth in stellar mass to $\sim8\times10^{11}\rm\,M_\sun$ at $z=0.45$. Although constituting only a minor pathway for the stellar growth of this BCG, persistent star formation from a residual cooling flow can nevertheless contribute significantly to the enormous number of globular clusters found around BCGs in the local Universe.
... In multiple cooling flow clusters significant (10 9 -10 10 M ) amounts of molecular gas have been detected in filaments which are sometimes coincident with buoyant X-ray bubbles rising through the ICM (e.g. McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Russell et al. , 2017bVantyghem et al. 2016Vantyghem et al. , 2018, and sometimes present throughout the inner ICM (Temi et al. 2018;Rose et al. 2019;Juráňová et al. 2019). It is not currently known if this cold gas has recently cooled from low-entropy gas lifted by the bubble, or is stimulated to cool in-situ by its passing. ...
We present high-resolution (synthesised beam size 0.″088×0.″083 or 25 × 23 pc2) Atacama Large Millimetre/submillimetre Array (ALMA) 12CO(2–1) line and 236 GHz continuum observations, as well as 5 GHz enhanced Multi-Element Radio Linked Interferometer Network (e-MERLIN) continuum observations, of NGC 0708; the brightest galaxy in the low-mass galaxy cluster Abell 262. The line observations reveal a turbulent, rotating disc of molecular gas in the core of the galaxy, and a high-velocity, blue-shifted feature ≈0.″4 (≈113 pc) from its centre. The sub-millimetre continuum emission peaks at the nucleus, but extends towards this anomalous CO emission feature. No corresponding elongation is found on the same spatial scales at 5 GHz with e-MERLIN. We discuss potential causes for the anomalous blue-shifted emission detected in this source, and conclude that it is most likely to be a low-mass in-falling filament of material condensing from the hot intra-cluster medium via chaotic cold accretion, but it is also possible that it is a jet-driven molecular outflow. We estimate the physical properties this structure has in these two scenarios, and show that either explanation is viable. We suggest future observations with integral field spectrographs will be able to determine the true cause of this anomalous emission, and provide further evidence for interaction between quenched cooling flows and mechanical feedback on both small and large scales in this source.
... In multiple cooling flow clusters significant (10 9 -10 10 M ) amounts of molecular gas have been detected in filaments which are sometimes coincident with buoyant X-ray bubbles rising through the ICM (e.g. McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Russell et al. , 2017bVantyghem et al. 2016Vantyghem et al. , 2018, and sometimes present throughout the inner ICM (Temi et al. 2018;Rose et al. 2019;Juráňová et al. 2019). It is not currently known if this cold gas has recently cooled from low-entropy gas lifted by the bubble, or is stimulated to cool in-situ by its passing. ...
We present high-resolution (synthesised beam size 0."088x0."083 or 25x23 pc$^2$) Atacama Large Millimetre/submillimetre Array (ALMA) $^{12}$CO(2-1) line and 236 GHz continuum observations, as well as 5 GHz enhanced Multi-Element Radio Linked Interferometer Network (e-MERLIN) continuum observations, of NGC 0708; the brightest galaxy in the low-mass galaxy cluster Abell 262. The line observations reveal a turbulent, rotating disc of molecular gas in the core of the galaxy, and a high-velocity, blue-shifted feature ~0."4 (~113 pc) from its centre. The sub-millimetre continuum emission peaks at the nucleus, but extends towards this anomalous CO emission feature. No corresponding elongation is found on the same spatial scales at 5 GHz with e-MERLIN. We discuss potential causes for the anomalous blue-shifted emission detected in this source, and conclude that it is most likely to be a low-mass in-falling filament of material condensing from the hot intra-cluster medium via chaotic cold accretion, but it is also possible that it is a jet-driven molecular outflow. We estimate the physical properties this structure has in these two scenarios, and show that either explanation is viable. We suggest future observations with integral field spectrographs will be able to determine the true cause of this anomalous emission, and provide further evidence for interaction between quenched cooling flows and mechanical feedback on both small and large scales in this source.
... Above z ∼ 0.3, most existing BCG gas masses come from targeted observations of known exceptional objects. These include the BCGs in Abell 1664 (z = 0.128; Russell et al. 2014), Abell 1835McNamara et al. 2014), the Phoenix cluster (z = 0.596; Russell et al. 2017), and SpARCS 1049 (z = 1.709; Webb et al. 2017). ...
We present ALMA CO (2-1) detections of 24 star-forming Brightest Cluster Galaxies (BCGs) over $0.2<z<1.2$, constituting the largest and most distant sample of molecular gas measurements in BCGs to date. The BCGs are selected from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) to be IR-bright and therefore star-forming. We find that molecular gas is common in star-forming BCGs, detecting CO at a detection rate of 80% in our target sample of 30 objects. We additionally provide measurements of the star formation rate (SFR) and stellar mass, calculated from existing MIPS 24 $\mu$m and IRAC 3.6 $\mu$m fluxes, respectively. We find these galaxies have molecular gas masses of $0.7-11.0\times 10^{10}\ \mathrm{M}_\odot$, comparable to other BCGs in this redshift range, and specific star formation rates which trace the Elbaz et al. (2011) Main Sequence. We compare our BCGs to those of the lower-redshift, cooling-flow BCG sample assembled by Edge (2001) and find that at z $\lesssim 0.6$ the two samples show very similar correlations between their gas masses and specific SFRs. We suggest that, in this redshift regime, the $\sim10\%$ (Webb et al., 2015) of BCGs that are star-forming process any accreted molecular gas into stars through means that are agnostic to both their redshift and their cluster mass.
... Qualitatively, this agrees with observations of large reservoirs of cold gas found in BCGs (e.g. Salomé et al. 2008;McNamara et al. 2014;Russell et al. 2014) and the enhanced fraction of X-ray AGN found in BCGs relative to satellites (i.e. Yang et al. 2018b). ...
We present an analysis of the X-ray active galactic nucleus (AGN) population in a sample of seven massive galaxy clusters in the redshift range 0.35 < z < 0.45. We utilize high-quality Chandra X-ray imaging to robustly identify AGN and precisely determine cluster masses and centroids. Follow-up VIsible Multi-Object Spectrograph optical spectroscopy allows us to determine which AGN are cluster members. Studying the subset of AGN with 0.5–8 keV luminosities >6.8 × 1042 erg s−1, within r ≤ 2r500 (approximately the virial radius), we find that the cluster AGN space density scales with cluster mass as $\sim M^{-2.0^{+0.8}_{-0.9}}$. This result rules out zero mass dependence of the cluster X-ray AGN space density at the 2.5σ level. We compare our cluster X-ray AGN sample to a control field with identical selection and find that the cluster AGN fraction is significantly suppressed relative to the field when considering the brightest galaxies with V < 21.5. For fainter galaxies, this difference is not present. Comparing the X-ray hardness ratios of cluster member AGN to those in the control field, we find no evidence for enhanced X-ray obscuration of cluster member AGN. Lastly, we see tentative evidence that disturbed cluster environments may contribute to enhanced AGN activity.
... It was originally thought that left unabated, high central radiative losses would result in the formation of a cooling flow (Fabian 1994), leading to large quantities of cold gas dropping out of the ICM and hence massive molecular reservoirs and high star formation rates (SFRs) within cluster cen-tres. However, cluster cores typically show only moderate molecular gas content (Fogarty et al. 2019;Castignani et al. 2020;McNamara et al. 2014;Russell et al. 2014Russell et al. , 2017Russell et al. , 2019 and low SFRs Donahue et al. 2010;Cooke et al. 2016;Fogarty et al. 2017), although there can be exceptions (e.g., Crawford et al. 1999;Egami et al. 2006;Von Der Linden et al. 2007;Mittal et al. 2015;Fogarty et al. 2017). Additionally, direct observational signatures of the cooling, such as X-ray emission lines below 1 keV are absent from numerous observations (e.g., Ikebe et al. 1997;Makishima et al. 2001;Peterson et al. 2001Peterson et al. , 2003Tamura et al. 2001;Böhringer et al. 2002;Matsushita et al. 2002;Lewis et al. 2002) and UV detections of O VI lines suggest lower than expected cooling rates (e.g., Oegerle et al. 2001;Bregman et al. 2006;Donahue et al. 2017). ...
While there is overwhelming observational evidence of AGN-driven jets in galaxy clusters and groups, if and how the jet energy is delivered to the ambient medium remains unanswered. Here we perform very high resolution AGN jet simulations within a live, cosmologically evolved cluster with the moving mesh code AREPO. We find that mock X-ray and radio lobe properties are in good agreement with observations with different power jets transitioning from FR-I to FR-II-like morphologies. During the lobe inflation phase, heating by both internal and bow shocks contributes to lobe energetics, and ~40 per cent of the feedback energy goes into the PdV work done by the expanding lobes. Low power jets are more likely to simply displace gas during lobe inflation, but higher power jets become more effective at driving shocks and heating the intracluster medium (ICM), although shocks rarely exceed $\mathcal{M}$~2-3. Once the lobe inflation phase ceases, cluster weather significantly impacts the lobe evolution. Lower power jet lobes are more readily disrupted and mixed with the ICM, depositing up to ~70 per cent of the injected energy, however, ultimately the equivalent of $\gtrsim$50 per cent of the feedback energy ends up as potential energy of the system. Even though the mean ICM entropy is increased up to 80 Myr after the jets switch off, AGN heating is gentle, inducing no large variations in cluster radial profiles in accord with observations.
... Greve et al. 2005;Gao et al. 2001;Schulz et al. 2007). Instead, the velocity dispersion of the molecular gas matches the dispersion seen in nearby clusters of galaxies in which a small fraction of the intracluster gas is cooling Russell et al. 2014;Gonzalez et al. 2005). ...
Cosmological simulations, as well as mounting evidence from observations, have shown that supermassive black holes play a fundamental role in regulating the formation of stars throughout cosmic time. This has been clearly demonstrated in the case of galaxy clusters in which powerful feedback from the central black hole is preventing the hot intracluster gas from cooling catastrophically, thus reducing the expected star formation rates by orders of magnitude. These conclusions have however been almost entirely based on nearby clusters. Based on new Chandra X-ray observations, we present the first observational evidence for massive, runaway cooling occurring in the absence of supermassive black hole feedback in the high-redshift galaxy cluster SpARCS104922.6+564032.5 ($z=1.709$). The hot intracluster gas appears to be fueling a massive burst of star formation ($\approx900$~M$_\odot$yr$^{-1}$) that is offset by dozens of kpc from the central galaxy. The burst is co-spatial with the coolest intracluster gas but not associated with any galaxy in the cluster. In less than 100 million years, such runaway cooling can form the same amount of stars as in the Milky Way. Intracluster stars are therefore not only produced by tidal stripping and the disruption of cluster galaxies, but can also be produced by runaway cooling of hot intracluster gas at early times. Overall, these observations show the dramatic impact when supermassive black hole feedback fails to operate in clusters. They indicate that in the highest overdensities such as clusters and proto-clusters, runaway cooling may be a new and important mechanism for fueling massive bursts of star formation in the early universe.
... Evidence for outflowing atomic gas has been found in both powerful RLAGN (e.g., Tadhunter, 1991) and 'radio-quiet' systems with smallscale jets (e.g., Morganti et al., 1998;Rupke and Veilleux, 2011) -see Morganti and Oosterloo (2018) for a recent overview of outflow properties inferred from HI absorption studies. There is growing evidence, particular from recent ALMA studies, of massive outflows of molecular material entrained or uplifted by jets or rising radio lobes (e.g., Alatalo et al., 2011;Dasyra et al., 2015;McNamara et al., 2014;Russell et al., 2014;Tremblay et al., 2018). A number of these examples are cool-core clusters, the environments in which AGN feedback is required to act most strongly to suppress cooling and star formation. ...
We review current understanding of the population of radio galaxies and radio-loud quasars from an observational perspective, focusing on their large-scale structures and dynamics. We discuss the physical conditions in radio galaxies, their fuelling and accretion modes, host galaxies and large-scale environments, and the role(s) they play as engines of feedback in the process of galaxy evolution. Finally we briefly summarise other astrophysical uses of radio galaxy populations, including the study of cosmic magnetism and cosmological applications, and discuss future prospects for advancing our understanding of the physics and feedback behaviour of radio galaxies.
... We tentatively hypothesize that secular-driven processes involving nonaxisymmetric stellar structures, such as bars and spiral arms, can trigger a large inflow of gas from the large-scale disk into nuclear regions of late-type galaxies, slowly feeding SMBHs and fueling star formation (e.g., Kormendy 1993Kormendy , 2013Kormendy & Kennicutt 2004;Fisher & Drory 2008;Leitner 2012;Cisternas et al. 2013;Tonini et al. 2016;Dullo et al. 2019). Barred galaxies make up the bulk (∼62%) of the late-type 12 Massive early-type galaxies and some BCGs can acquire cold gas through the cooling of hot gas and/or via cannibalism of a gas-rich satellite, and they may undergo episodes of low level star formation at low redshift (Salomé & Combes 2003;O'Dea et al. 2008;Hopkins & Hernquist 2009;Struve et al. 2010;Young et al. 2011;Zubovas & King 2012;Russell et al. 2014Russell et al. , 2019Smith & Edge 2017;Krajnović et al. 2020). galaxies in our sample (Figure 4). ...
The tight correlations between supermassive black hole (SMBH) mass ( M BH ) and the properties of the host galaxy have useful implications for our understanding of the growth of SMBHs and of the evolution of galaxies. Here, we present newly observed correlations between M BH and the host galaxy total UV−[3.6] color ( , Pearson's r = 0.6–0.7) for a sample of 67 galaxies (20 early-type galaxies and 47 late-type galaxies) with directly measured M BH in the Galaxy Evolution Explorer/S ⁴ G survey. The colors are carefully measured in a homogeneous manner using the far-UV, near-UV, and 3.6 μ m magnitudes of the galaxies and their multicomponent structural decompositions in the literature. We find that more massive SMBHs are hosted by (early- and late-type) galaxies with redder colors, but the relations for the two morphological types have slopes that differ at ∼2 σ level. Early-type galaxies define a red sequence in the diagrams, while late-type galaxies trace a blue sequence. Within the assumption that the specific star formation rate of a galaxy (sSFR) is well traced by L UV / L 3.6 , it follows that the SMBH masses for late-type galaxies exhibit a steeper dependence on sSFR than those for early-type galaxies. The and M BH − L 3.6,tot relations for the sample galaxies reveal a comparable level of vertical scatter in the log M BH direction, approximately 5%–27% more than the vertical scatter of the M BH − σ relation. Our relations suggest different channels of SMBH growth for early- and late-type galaxies, consistent with their distinct formation and evolution scenarios. These new relations offer the prospect of estimating SMBH masses reliably using the galaxy color alone. Furthermore, we show that they are capable of estimating intermediate black hole masses in low-mass early- and late-type galaxies.
... Cold molecular gas has been found to form in the central dominant galaxies (CDGs) of several systems (e.g., Edge 2001;Salomé & Combes 2003, and more recently, Tremblay et al. 2016;Vantyghem et al. 2017;O'Sullivan et al. 2018;Rose et al. 2019b). In these studies, single-dish CO measurements have turned out to be essential to reveal the total molecular gas resulting from cooling in the centers of groups and clusters (McNamara & Nulsen 2007;Russell et al. 2014;McNamara et al. 2016;Russell et al. 2016Russell et al. , 2017aRussell et al. , 2017b. However, in order to make a comparison to feedback models, a more precise location of these cold-gas reservoirs is needed: Are they associated in small or large clouds, or fully diffuse? ...
The fate of cooling gas in the centers of galaxy clusters and groups is still not well understood, as is also the case for the complex processes of triggering star formation in central dominant galaxies, reheating of cooled gas by active galactic nuclei (AGN), and the triggering or “feeding” of supermassive black hole outbursts. We present CO observations of the early-type galaxy NGC 5044, which resides at the center of an X-ray bright group with a moderate cooling flow. For our analysis we combine CO(2−1) data from the 7 m antennae of the Atacama Compact Array (ACA) and the ACA total power array (TP). We demonstrate, using the 7 m array data, that we can recover the total flux inferred from IRAM 30 m single-dish observations, which corresponds to a total molecular mass of about 4 × 10 ⁷ M ⊙ . Most of the recovered flux is blueshifted with respect to the galaxy rest frame and is extended on kiloparsec-scales, suggesting low filling factor dispersed clouds. We find eight concentrations of molecular gas out to a radius of 10″ (1.5 kpc), which we identify with giant molecular clouds. The total molecular gas mass is more centrally concentrated than the X-ray emitting gas, but is extended in the northeast-southwest direction beyond the IRAM 30 m beam. We also compare the spatial extent of the molecular gas to the H α emission: The CO emission coincides with the very bright H α region in the center. We do not detect CO emission in the fainter H α regions. Furthermore, we find two CO absorption features spatially located at the center of the galaxy, within 5 pc projected distance of the AGN, infalling at 255 and 265 km s ⁻¹ relative to the AGN. This indicates that the two giant molecular clouds seen in absorption are most likely within the sphere of influence of the supermassive black hole.
... Still in connection with radio jets, but on much larger scales, the last few years has seen the ubiquitous detection of molecular filaments in the vicinity of the bright central galaxies (BCG) of galaxy clusters, which are generally radio galaxies. These molecular structure extend from a few kpc to several tens kpc, have molecular gas masses in the range of 10 8 -10 10 M , and generally are seen to trail the X-ray hot cavity inflated by the radio jets (Russell et al. 2014(Russell et al. , 2017bTremblay et al. 2018;Vantyghem et al. 2018Vantyghem et al. , 2019Olivares et al. 2019). The velocity gradients along the filaments are smooth and shallow, and generally inconsistent with free-fall. ...
Neutral-atomic and molecular outflows are a common occurrence in galaxies, near and far. They operate over the full extent of their galaxy hosts, from the innermost regions of galactic nuclei to the outermost reaches of galaxy halos. They carry a substantial amount of material that would otherwise have been used to form new stars. These cool outflows may have a profound impact on the evolution of their host galaxies and environments. This article provides an overview of the basic physics of cool outflows, a comprehensive assessment of the observational techniques and diagnostic tools used to characterize them, a detailed description of the best-studied cases, and a more general discussion of the statistical properties of these outflows in the local and distant universe. The remaining outstanding issues that have not yet been resolved are summarized at the end of the review to inspire new research directions.
... These possibilities have been considered both by observational (e.g. Alatalo et al. 2011;Combes et al. 2013;Morganti et al. 2013;Russell et al. 2014) and numerical (e.g. Gaspari et al. 2012b; Li & Bryan 2014;Costa et al. 2015;Valentini & Brighenti 2015) studies. ...
We present simulations of galaxy formation, based on the GADGET-3 code, in which a sub-resolution model for star formation and stellar feedback is interfaced with a new model for AGN feedback. Our sub-resolution model describes a multiphase ISM, accounting for hot and cold gas within the same resolution element: we exploit this feature to investigate the impact of coupling AGN feedback energy to the different phases of the ISM over cosmic time. Our fiducial model considers that AGN feedback energy coupling is driven by the covering factors of the hot and cold phases. We perform a suite of cosmological hydrodynamical simulations of disc galaxies ($M_{\rm halo, \, DM} \simeq 2 \cdot 10^{12}$ M$_{\odot}$, at $z=0$), to investigate: $(i)$ the effect of different ways of coupling AGN feedback energy to the multiphase ISM; $(ii)$ the impact of different prescriptions for gas accretion (i.e. only cold gas, both cold and hot gas, with the additional possibility of limiting gas accretion from cold gas with high angular momentum); $(iii)$ how different models of gas accretion and coupling of AGN feedback energy affect the coevolution of supermassive BHs and their host galaxy. We find that at least a share of the AGN feedback energy has to couple with the diffuse gas, in order to avoid an excessive growth of the BH mass. When the BH only accretes cold gas, it experiences a growth that is faster than in the case in which both cold and hot gas are accreted. If the accretion of cold gas with high angular momentum is reduced, the BH mass growth is delayed, the BH mass at $z=0$ is reduced by up to an order of magnitude, and the BH is prevented from accreting below $z \lesssim 2$, when the galaxy disc forms.
... Reservoirs of cold gas detected at centers of cool core clusters cast new light on the fueling of supermassive black holes (Edge 2001;Russell et al. 2014Russell et al. , 2016Russell et al. , 2017Vantyghem et al. 2016;McNamara et al. 2016). The prevailing AGN feedback model suggests that thermal instability can happen if the ratio of the cooling time t cool and the freefall time = t r g 2 ff ( )drops below a threshold value (McCourt et al. 2012). ...
Molecular cold gas and star formation have been observed at centers of cool core clusters, albeit at a level much smaller than expected from the classic cooling model. Feedback from the supermassive black hole is likely to have prevented hot gas from cooling. However, the exact cooling and heating processes are poorly understood. The missing key piece is the link between the hot gas (10 ⁷ K) and cold gas (10 ³ K). Using the extreme ultraviolet spectrometer on board Hisaki , we explore a distant galaxy cluster, RCS2 J232727.6-020437, one of the most massive cool core clusters with a cooling rate of 400 M ⊙ yr ⁻¹ . We aim to detect gas at intermediate temperatures (3×10 ⁴ K) emitting He i α and He i β at rest wavelengths of 58.4 nm and 53.7 nm, respectively. Our target resides at z = 0.6986, for which these He i lines shift away from the absorption of the Galaxy. Our findings show that the amount of 10 4–5 K gas at the center of this cluster is smaller than expected if cooling there was uninhibited, which demonstrates that feedback both operates and is efficient for massive clusters at these epochs.
... In the ensuing half century, it has become clear that condensation phenomena in very diverse astrophysical environments may be due to TI. For example, ALMA observations have provided strong evidence that TI operates in the central regions of cool-core clusters and within brightest cluster galaxies and brightest group galaxies (e.g., David et al. 2014;McNamara et al. 2014;Russell et al. 2014Russell et al. , 2016Voit et al. 2015;Tremblay et al. 2016;Vantyghem et al. 2016;Pulido et al. 2018;Temi et al. 2018), as molecular gas must co-exist with the hot virialized plasma temperatures of the intracluster medium (ICM) or intergroup medium. The relatively low temperature (T∼10 4 K) gas recently inferred to be present in the circumgalactic medium (CGM) of galaxies is likely also due to TI (Stocke et al. 2013;Werk et al. 2013;Stern et al. 2016; see Tumlinson et al. 2017 for a review). ...
Multiphase media have very complex structure and evolution. Accurate numerical simulations are necessary to make advances in our understanding of this rich physics. Because simulations can capture both the linear and nonlinear evolution of perturbations with a relatively wide range of sizes, it is important to thoroughly understand the stability of condensation and acoustic modes between the two extreme wavelength limits of isobaric and isochoric instability as identified by Field. Partially motivated by a recent suggestion that large non-isobaric clouds can “shatter” into tiny cloudlets, we revisit the linear theory to survey all possible regimes of thermal instability. We uncover seven regimes in total, one of which allows three unstable condensation modes. Using the code Athena++ , we determine the numerical requirements to properly evolve small amplitude perturbations of the entropy mode into the nonlinear regime. Our 1D numerical simulations demonstrate that for a typical AGN cooling function, the nonlinear evolution of a single eigenmode in an isobarically unstable plasma involves increasingly larger amplitude oscillations in cloud size, temperature, and density as the wavelength increases. Such oscillations are the hallmark behavior of non-isobaric multiphase gas dynamics and may be observable as correlations between changes in brightness and the associated periodic redshifts and blueshifts in systems that can be spatially resolved. Intriguingly, we discuss regimes and derive characteristic cloud sizes for which the saturation process giving rise to these oscillations can be so energetic that the cloud may indeed break apart. However, we dub this process “splattering” instead of “shattering,” as it is a different fragmentation mechanism that is triggered when the cloud suddenly “lands” on the stable cold branch of the equilibrium curve.
Multiwavelength studies indicate that nuclear activity and bulge properties are closely related, but the details remain unclear. To study this further, we combine Hubble Space Telescope bulge structural and photometric properties with 1.5 GHz, e-MERLIN nuclear radio continuum data from the LeMMINGs survey for a large sample of 173 ‘active’ galaxies (LINERs and Seyferts) and ‘inactive’ galaxies (H iis and absorption line galaxies, ALGs). Dividing our sample into active and inactive, they define distinct (radio core luminosity)–(bulge mass), $L_{\rm R,core}-M_{*, \rm bulge}$, relations, with a mass turnover at $M_{*, \rm bulge}\sim 10^{9.8 \pm 0.3} \rm { M_{\odot }}$ (supermassive black hole mass $M_{\rm BH} \sim 10^{6.8 \pm 0.3} \rm M_{\odot }$), which marks the transition from AGN-dominated nuclear radio emission in more massive bulges to that mainly driven by stellar processes in low-mass bulges. None of our 10/173 bulgeless galaxies host an AGN. The AGN fraction increases with increasing $M_{*,\rm bulge}$ such that $f_{\rm optical\_AGN}\propto M_{*,\rm bulge}^{0.24 \pm 0.06}$ and $f_{\rm radio\_AGN}\propto M_{*,\rm bulge}^{0.24 \pm 0.05}$. Between $M_{*,\rm bulge}\sim 10^{8.5}$ and $10^{11.3} \rm M_{\odot }$, $f_{\rm optical\_AGN}$ steadily rises from 15 ± 4 to 80 ± 5 per cent. We find that at fixed bulge mass, the radio loudness, nuclear radio activity and the (optical and radio) AGN fraction exhibit no dependence on environment. Radio-loud hosts preferentially possess an early-type morphology than radio-quiet hosts, the two types are however indistinguishable in terms of bulge Sérsic index and ellipticity, while results on the bulge inner logarithmic profile slope are inconclusive. We finally discuss the importance of bulge mass in determining the AGN triggering processes, including potential implications for the nuclear radio emission in nearby galaxies.
AGN feedback stands for the dramatic impact that a SMBH can make on its environment. It has become an essential element of models that describe the formation and evolution of baryons in massive virialized halos. The baryons' radiative losses in the cores of these halos might lead to massive cooling and vigorous star formation on the order of 10-1000 Msun/yr, whereas observations show that the star formation rates are considerably less. It has now become clear from an observational, theoretical and simulation perspective that the activity of the central SMBH compensates for gas cooling losses and prevents very high star formation rates in massive galaxies, which otherwise would be much brighter than observed today. While AGN feedback is important over a broad range of halo masses, the most massive objects like galaxy groups and clusters truly provide outstanding laboratories for understanding the intrinsic details of AGN feedback. Partly, this is because in the nearby massive objects we can directly see what AGN feedback is doing to its surrounding hot halo in exquisite details, as opposed to less massive systems. Yet another reason is that in the most massive objects, the magnitude of AGN feedback has to be extremely large, providing the most stringent constraints. In a nutshell, the AGN feedback paradigm in groups and clusters postulates that (i) a SMBH in the center of a halo can release a vast amount of energy, (ii) this energy can be intercepted and thermalized by the gaseous atmosphere and (iii) the system self-regulates so that the energy released scales with the properties of the halo. A combination of multi-wavelength observations provides compelling evidence of the AGN feedback importance. Similarly, theoretical arguments suggest that self-regulation might be a natural property of a system consisting of a gaseous atmosphere and a SMBH at the bottom of the potential well.
The universe’s biggest galaxies have both vast atmospheres and supermassive central black holes. This article reviews how those two components of a large galaxy couple and regulate the galaxy’s star formation rate. Models of interactions between a supermassive black hole and the large-scale atmosphere suggest that the energy released as cold gas clouds accrete onto the black hole suspends the atmosphere in a state that is marginally stable to formation of cold clouds. A growing body of observational evidence indicates that many massive galaxies, ranging from the huge central galaxies of galaxy clusters down to our own Milky Way, are close to that marginal state. The gas supply for star formation within a galaxy in such a marginal state is closely tied to the central velocity dispersion (σv) of its stars. We therefore explore the consequences of a model in which energy released during black-hole accretion shuts down star formation when σv exceeds a critical value determined by the galaxy’s supernova heating rate.
While there is overwhelming observational evidence of AGN-driven jets in galaxy clusters and groups, if and how the jet energy is delivered to the ambient medium remains unanswered. Here we perform very high resolution AGN jet simulations within a live, cosmologically evolved cluster with the moving mesh code arepo. We find that mock X-ray and radio lobe properties are in good agreement with observations with different power jets transitioning from FR-I to FR-II-like morphologies. During the lobe inflation phase, heating by both internal and bow shocks contributes to lobe energetics, and ∼40 per cent of the feedback energy goes into the PdV work done by the expanding lobes. Low power jets are more likely to simply displace gas during lobe inflation, but higher power jets become more effective at driving shocks and heating the intracluster medium (ICM), although shocks rarely exceed $\mathcal {M}\sim 2-3$. Once the lobe inflation phase ceases, cluster weather significantly impacts the lobe evolution. Lower power jet lobes are more readily disrupted and mixed with the ICM, depositing up to ∼70 per cent of the injected energy, however, ultimately the equivalent of ${\,\, \gtrsim \,\,}50$ per cent of the feedback energy ends up as potential energy of the system. Even though the mean ICM entropy is increased up to 80 Myr after the jets switch off, AGN heating is gentle, inducing no large variations in cluster radial profiles in accord with observations.
We present ALMA CO (2-1) detections of 24 star-forming brightest cluster galaxies (BCGs) over 0.2 < z < 1.2, constituting the largest and most distant sample of molecular gas measurements in BCGs to date. The BCGs are selected from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) to be IR-bright and therefore star-forming. We find that molecular gas is common in star-forming BCGs, detecting CO at a detection rate of 80% in our target sample of 30 objects. We additionally provide measurements of the star formation rate and stellar mass, calculated from existing MIPS 24 μm and IRAC 3.6 μm fluxes, respectively. We find these galaxies have molecular gas masses of 0.7-11.0 × 1010 M o˙, comparable to other BCGs in this redshift range, and specific star formation rates that trace the main sequence of Elbaz et al. We compare our BCGs to those of the lower-redshift, cooling-flow BCG sample assembled by Edge and find that at z ≲ 0.6 the two samples show very similar correlations between their gas masses and specific SFRs. We suggest that, in this redshift regime, the ∼10% of BCGs that are star-forming process accreted molecular gas into stars through means that are agnostic to both their redshift and their cluster mass. © 2021. The American Astronomical Society. All rights reserved..
We present an analysis of new and archival ALMA observations of molecular gas in 12 central cluster galaxies. We examine emerging trends in molecular filament morphology and gas velocities to understand their origins. Molecular gas masses in these systems span $10^9 {--}10^{11} {\rm \, M_{\odot }}$, far more than most gas-rich galaxies. ALMA images reveal a distribution of morphologies from filamentary to disc-dominated structures. Circumnuclear discs on kiloparsec scales appear rare. In most systems, half to nearly all of the molecular gas lies in filamentary structures with masses of a few $\times 10^{8{\text{--}}10}{\rm \, M_{\odot }}$ that extend radially several to several tens of kpc. In nearly all cases the molecular gas velocities lie far below stellar velocity dispersions, indicating youth, transience, or both. Filament bulk velocities lie far below the galaxy’s escape and free-fall speeds indicating they are bound and being decelerated. Most extended molecular filaments surround or lie beneath radio bubbles inflated by the central active galactic nuclei (AGNs). Smooth velocity gradients found along the filaments are consistent with gas flowing along streamlines surrounding these bubbles. Evidence suggests most of the molecular clouds formed from low entropy X-ray gas that became thermally unstable and cooled when lifted by the buoyant bubbles. Uplifted gas will stall and fall back to the galaxy in a circulating flow. The distribution in morphologies from filament to disc-dominated sources therefore implies slowly evolving molecular structures driven by the episodic activity of the AGNs.
Cosmological simulations, as well as mounting evidence from observations, have shown that supermassive black holes play a fundamental role in regulating the formation of stars throughout cosmic time. This has been clearly demonstrated in the case of galaxy clusters in which powerful feedback from the central black hole is preventing the hot intracluster gas from cooling catastrophically, thus reducing the expected star formation rates by orders of magnitude. These conclusions, however, have been almost entirely based on nearby clusters. Based on new Chandra X-ray observations, we present the first observational evidence for massive, runaway cooling occurring in the absence of supermassive black hole feedback in the high-redshift galaxy cluster SpARCS104922.6 + 564032.5 (z = 1.709). The hot intracluster gas appears to be fueling a massive burst of star formation (≈900 M⊙ yr⁻¹) that is offset by dozens of kpc from the central galaxy. The burst is co-spatial with the coolest intracluster gas but not associated with any galaxy in the cluster. In less than 100 million years, such runaway cooling can form the same amount of stars as in the Milky Way. Therefore, intracluster stars are not only produced by tidal stripping and the disruption of cluster galaxies, but can also be produced by runaway cooling of hot intracluster gas at early times. Overall, these observations show the dramatic impact when supermassive black hole feedback fails to operate in clusters. They indicate that in the highest overdensities, such as clusters and protoclusters, runaway cooling may be a new and important mechanism for fueling massive bursts of star formation in the early universe.
Passive early-type galaxies dominate cluster cores at z ≲ 1.5. At higher redshift, cluster core galaxies are observed to have on-going star-formation, which is fueled by cold molecular gas. We measured the molecular gas reservoir of the central region around the radio-loud active galactic nucleus (AGN) in the cluster CARLA J1103 + 3449 at z = 1.44 using NOEMA. The AGN synchrotron emission dominates the continuum emission at 94.48 GHz, and we measured its flux at the AGN position and at the position of two radio jets. Combining our measurements with published results over the range 4.71–94.5 GHz, and assuming S synch ∝ ν − α , we obtain a flat spectral index of α = 0.14 ± 0.03 for the AGN core emission, and a steeper index of α = 1.43 ± 0.04 and α = 1.15 ± 0.04 at positions close to the western and eastern lobes, respectively. The total spectral index is α = 0.92 ± 0.02 over the range 73.8 MHz–94.5 GHz. We detect two CO(2–1) emission lines, both blueshifted with respect to the AGN. Their emission corresponds to two regions, ~17 kpc southeast and ~14 kpc southwest of the AGN, not associated with galaxies. In these two regions, we find a total massive molecular gas reservoir of M gas tot = 3.9 ± 0.4 × 10 ¹⁰ M ⊙ , which dominates (≳60%) the central total molecular gas reservoir. These results can be explained by massive cool gas flows in the center of the cluster. The AGN early-type host is not yet quenched; its star formation rate is consistent with being on the main sequence of star-forming galaxies in the field (star formation rate ~30 – 140 M ⊙ yr ⁻¹ ), and the cluster core molecular gas reservoir is expected to feed the AGN and the host star formation before quiescence. The other confirmed cluster members show star formation rates at ~2 σ below the field main sequence at similar redshifts and do not have molecular gas masses larger than galaxies of similar stellar mass in the field.
Brightest cluster galaxies (BCGs) are excellent laboratories for the study of galaxy evolution in dense Mpc-scale environments. We used the IRAM-30 m to observe, in CO(1→0), CO(2→1), CO(3→2), or CO(4→3), 18 BCGs at z ∼ 0.2 − 0.9 drawn from the Cluster Lensing And Supernova survey with Hubble (CLASH) survey. Our sample includes RX1532, which is our primary target as it is among the BCGs with the highest star formation rate (SFR ≳100 M ⊙ yr ⁻¹ ) in the CLASH sample. We unambiguously detected both CO(1→0) and CO(3→2) in RX1532, yielding a large reservoir of molecular gas, M H 2 = (8.7 ± 1.1)×10 ¹⁰ M ⊙ , and a high level of excitation, r 31 = 0.75 ± 0.12. A morphological analysis of the Hubble Space Telescope I-band image of RX1532 reveals the presence of clumpy substructures both within and outside the half-light radius r e = (11.6 ± 0.3) kpc, similarly to those found independently both in ultraviolet and in H α in previous works. We tentatively detected CO(1→0) or CO(2→1) in four other BCGs, with molecular gas reservoirs in the range of M H 2 = 2 × 10 10 − 11 M ⊙ . For the remaining 13 BCGs, we set robust upper limits of M H 2 / M ⋆ ≲ 0.1, which are among the lowest molecular-gas-to-stellar-mass ratios found for distant ellipticals and BCGs. In comparison with distant cluster galaxies observed in CO, our study shows that RX1532 ( M H 2 / M ⋆ = 0.40 ± 0.05) belongs to the rare population of star-forming and gas-rich BCGs in the distant universe. By using the available X-ray based estimates of the central intra-cluster medium entropy, we show that the detection of large reservoirs of molecular gas M H 2 ≳ 10 ¹⁰ M ⊙ in distant BCGs is possible when the two conditions are met: (i) high SFR and (ii) low central entropy, which favors the condensation and the inflow of gas onto the BCGs themselves, similarly to what has been previously found for some local BCGs.
Recent molecular line observations with ALMA and NOEMA in several Brightest Cluster Galaxies (BCG) have revealed the large-scale filamentary structure at the center of cool core clusters. These filaments extend over 20-100kpc, they are tightly correlated with ionized gas (Hα, [NII]) emission, and have characteristic shapes: either radial and straight, or also showing a U-turn, like a horse-shoe structure. The kinematics is quite regular and laminar, and the derived infall time is much longer than the free-fall time. The filaments extend up to the radius where the cooling time becomes larger than the infall time. Filaments can be perturbed by the sloshing of the BCG in its cluster, and spectacular cooling wakes have been observed. Filaments tend to occur at the border of cavities driven in the X-ray gas by the AGN radio jets. Observations of cool core clusters support the thermal instability scenario, which accounts for the multiphase medium in the upper atmospheres of BCG, where the right balance between heating and cooling is reached, and a chaotic cold gas accretion occurs. Molecular filaments are also seen associated to ram-pressure stripped spiral galaxies in rich galaxy clusters, and in jet-induced star formation, suggesting a very efficient molecular cloud formation even in hostile cluster environments.
Today, the brightest cluster galaxies (BCGs) are passive and very massive galaxies at the center of their clusters, and they still accrete mass through swallowing companions and gas from cooling flows. However their formation history is not well known. We report CO(4→3) and continuum map observations of the SpARCS1049+56 BCG at z = 1.709, one of the most distant known BCGs. Our observations yield M H 2 < 1.1 × 10 ¹⁰ M⊙ for the BCG; while in CO(4→3), we detect two gas-rich companions at the northeast and southeast of the BCG, within 20 kpc, with LCO(4→3)′ = (5.8±0.6) × 10 ⁹ K km s ⁻¹ pc ² and (7.4 ± 0.7)×10 ⁹ K km s ⁻¹ pc ² , respectively. The northern companion is associated with a pair of merging cluster galaxies, while the southern one shows a southern tail in CO(4→3), which was also detected in continuum, and we suggest it to be the most distant jellyfish galaxy for which ram pressure stripping is effectively able to strip off its dense molecular gas. This study probes the presence of rare gas-rich systems in the very central region of a distant cluster core, which will potentially merge into the BCG itself. Currently, we may thus be seeing the reversal of the star formation versus density relation at play in the distant universe. This is the first time the assembly of high- z progenitors of our local BCGs can be studied in such great detail.
The mechanisms governing the stellar mass assembly and star formation history of brightest cluster galaxies (BCGs) are still being debated. By means of new and archival molecular gas observations we investigate the role of dense megaparsec-scale environments in regulating the fueling of star formation in distant BCGs, through cosmic time. We observed in CO with the IRAM 30 m telescope two star-forming BCGs belonging to SpARCS clusters, namely, 3C 244.1 ( z = 0.4) and SDSS J161112.65+550823.5 ( z = 0.9), and compared their molecular gas and star formation properties with those of a compilation of ∼100 distant cluster galaxies from the literature, including nine additional distant BCGs at z ∼ 0.4 − 3.5. We set robust upper limits of M H 2 < 1.0 × 10 ¹⁰ M⊙ and < 2.8 × 10 ¹⁰ M⊙ to their molecular gas content, respectively, and to the ratio of molecular gas to stellar mass M (H 2 )/ M⋆ ≲ 0.2 and depletion time τdep ≲ 40 Myr of the two targeted BCGs. They are thus among the distant cluster galaxies with the lowest gas fractions and shortest depletion times. The majority (64%±15% and 73%±18%) of the 11 BCGs with observations in CO have lower M (H 2 )/ M⋆ values and τdep , respectively, than those estimated for main sequence galaxies. Statistical analysis also tentatively suggests that the values of M (H 2 )/ M⋆ and τdep for the 11 BCGs deviates, with a significance of ∼2 σ , from those of the comparison sample of cluster galaxies. A morphological analysis for a subsample of seven BCGs with archival HST observations reveals that 71%±17% of the BCGs are compact or show star-forming components or substructures. Our results suggest a scenario where distant star-forming BCGs assemble a significant fraction ∼16% of their stellar mass on the relatively short timescale ∼ τdep , while environmental mechanisms might prevent the replenishment of gas feeding the star formation. We speculate that compact components also favor the rapid exhaustion of molecular gas and ultimately help to quench the BCGs. Distant star-forming BCGs are excellent targets for ALMA and for next-generation telescopes such as the James Webb Space Telescope.
Multi-phase filamentary structures around brightest cluster galaxies (BCG) are likely a key step of AGN-feedback. We observed molecular gas in three cool cluster cores, namely Centaurus, Abell S1101, and RXJ1539.5, and gathered ALMA (Atacama Large Millimeter/submillimeter Array) and MUSE (Multi Unit Spectroscopic Explorer) data for 12 other clusters. Those observations show clumpy, massive, and long (3−25 kpc) molecular filaments, preferentially located around the radio bubbles inflated by the AGN. Two objects show nuclear molecular disks. The optical nebula is certainly tracing the warm envelopes of cold molecular filaments. Surprisingly, the radial profile of the H α /CO flux ratio is roughly constant for most of the objects, suggesting that (i) between 1.2 and 6 times more cold gas could be present and (ii) local processes must be responsible for the excitation. Projected velocities are between 100 and 400 km s ⁻¹ , with disturbed kinematics and sometimes coherent gradients. This is likely due to the mixing in projection of several thin (and as yet) unresolved filaments. The velocity fields may be stirred by turbulence induced by bubbles, jets, or merger-induced sloshing. Velocity and dispersions are low, below the escape velocity. Cold clouds should eventually fall back and fuel the AGN. We compare the radial extent of the filaments, rfil , with the region where the X-ray gas can become thermally unstable. The filaments are always inside the low-entropy and short-cooling-time region, where tcool / tff < 20 (9 of 13 sources). The range of tcool / tff of 8−23 at rfil , is likely due to (i) a more complex gravitational potential affecting the free-fall time tff (sloshing, mergers, etc.) and (ii) the presence of inhomogeneities or uplifted gas in the ICM, affecting the cooling time tcool . For some of the sources, rfil lies where the ratio of the cooling time to the eddy-turnover time, tcool / teddy , is approximately unity.
Context . Low luminosity radio galaxies (LLRGs) typically reside in dense megaparsec-scale environments and are often associated with brightest cluster galaxies (BCGs). They are an excellent tool to study the evolution of molecular gas reservoirs in giant ellipticals, even close to the active galactic nucleus.
Aims . We investigate the role of dense megaparsec-scale environment in processing molecular gas in LLRGs in the cores of galaxy (proto-)clusters. To this aim we selected within the COSMOS and DES surveys a sample of five LLRGs at z = 0.4−2.6 that show evidence of ongoing star formation on the basis of their far-infrared (FIR) emission.
Methods . We assembled and modeled the FIR-to-UV spectral energy distributions (SEDs) of the five radio sources to characterize their host galaxies in terms of stellar mass and star formation rate. We observed the LLRGs with the IRAM-30 m telescope to search for CO emission. We then searched for dense megaparsec-scale overdensities associated with the LLRGs using photometric redshifts of galaxies and the Poisson Probability Method, which we have upgraded using an approach based on the wavelet-transform ( w PPM), to ultimately characterize the overdensity in the projected space and estimate the radio galaxy miscentering. Color-color and color-magnitude plots were then derived for the fiducial cluster members, selected using photometric redshifts.
Results . Our IRAM-30 m observations yielded upper limits to the CO emission of the LLRGs, at z = 0.39, 0.61, 0.91, 0.97, and 2.6. For the most distant radio source, COSMOS-FRI 70 at z = 2.6, a hint of CO(7→6) emission is found at 2.2 σ . The upper limits found for the molecular gas content M (H 2 )/ M ⋆ < 0.11, 0.09, 1.8, 1.5, and 0.29, respectively, and depletion time τ dep ≲ (0.2−7) Gyr of the five LLRGs are overall consistent with the corresponding values of main sequence field galaxies. Our SED modeling implies large stellar-mass estimates in the range log( M ⋆ / M ⊙ ) = 10.9−11.5, typical for giant ellipticals. Both our w PPM analysis and the cross-matching of the LLRGs with existing cluster/group catalogs suggest that the megaparsec-scale overdensities around our LLRGs are rich (≲10 ¹⁴ M ⊙ ) groups and show a complex morphology. The color-color and color-magnitude plots suggest that the LLRGs are consistent with being star forming and on the high-luminosity tail of the red sequence. The present study thus increases the still limited statistics of distant cluster core galaxies with CO observations.
Conclusions . The radio galaxies of this work are excellent targets for ALMA as well as next-generation telescopes such as the James Webb Space Telescope.
We present recent Chandra X-ray observations of the RX J0821.0+0752 galaxy cluster, in addition to ALMA observations of the CO(1-0) and CO(3-2) line emission tracing the molecular gas in its central galaxy. All of the CO line emission, originating from a molecular gas reservoir, is located several kiloparsecs away from the nucleus of the central galaxy. The cold gas is concentrated into two main clumps surrounded by a diffuse envelope. They form a wide filament coincident with a plume of bright X-ray emission emanating from the cluster core. This plume encompasses a putative X-ray cavity that is only large enough to have uplifted a small percent of the molecular gas. Unlike other brightest cluster galaxies, stimulated cooling, where X-ray cavities lift low-entropy cluster gas until it becomes thermally unstable, cannot have produced the observed gas reservoir. Instead, the molecular gas has likely formed as a result of sloshing motions in the intracluster medium induced by a nearby galaxy. Sloshing can emulate uplift by dislodging gas from the galactic center. This gas has the shortest cooling time, so it will condense if disrupted for long enough. © 2019. The American Astronomical Society. All rights reserved.
Unresolved gas and dust observations show a surprising diversity in the amount of interstellar matter in early-type galaxies. Using ALMA observations we resolve the ISM in z$\sim$0.05 early-type galaxies. From a large sample of early-type galaxies detected in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) we selected five of the dustiest cases, with dust masses M$_d\sim$several$\times10^7$M$_\odot$, with the aim of mapping their submillimetre continuum and $^{12}$CO(2-1) line emission distributions. These observations reveal molecular gas disks. There is a lack of associated, extended continuum emission in these ALMA observations, most likely because it is resolved out or surface brightness limited, if the dust distribution is as extended as the CO gas. However, two galaxies have central continuum ALMA detections. An additional, slightly offset, continuum source is revealed in one case, which may have contributed to confusion in the Herschel fluxes. Serendipitous continuum detections further away in the ALMA field are found in another case. Large and massive rotating molecular gas disks are mapped in three of our targets, reaching a few$\times10^{9}$M$_\odot$. One of these shows evidence of kinematic deviations from a pure rotating disc. The fields of our two remaining targets contain only smaller, weak CO sources, slightly offset from the optical galaxy centres. These may be companion galaxies seen in ALMA observations, or background objects. These heterogeneous findings in a small sample of dusty early-type galaxies reveal the need for more such high spatial resolution studies, to understand statistically how dust and gas are related in early-type galaxies.
In many observed galaxy clusters, jets launched by the accretion process on to supermassive black holes, inflate large-scale cavities filled with energetic, relativistic plasma. This process is thought to be responsible for regulating cooling losses, thus moderating the inflow of gas on to the central galaxy, quenching further star formation and maintaining the galaxy in a red and dead state. In this paper, we implement a new jet feedback scheme into the moving mesh-code AREPO, contrast different jet injection techniques and demonstrate the validity of our implementation by comparing against simple analytical models. We find that jets can significantly affect the intracluster medium (ICM), offset the overcooling through a number of heating mechanisms, as well as drive turbulence, albeit within the jet lobes only. Jet-driven turbulence is, however, a largely ineffective heating source and is unlikely to dominate the ICM heating budget even if the jet lobes efficiently fill the cooling region, as it contains at most only a few per cent of the total injected energy. We instead show that the ICM gas motions, generated by orbiting substructures, while inefficient at heating the ICM, drive largescale turbulence and when combined with jet feedback, result in line-of-sight velocities and velocity dispersions consistent with the Hitomi observations of the Perseus cluster.
We present recent ALMA observations of the CO (1-0) and CO (3-2) emission lines in the brightest cluster galaxy of RXC J1504.1-0248, which is one of the most extreme cool core clusters known. The central galaxy contains 1.9 - 1010 M⊙ of molecular gas. The molecular gas morphology is complex and disturbed, showing no evidence for a rotationally supported structure in equilibrium. A total of 80% of the gas is situated within the central 5 kpc of the galactic center, while the remaining gas is located in a 20 kpc long filament. The cold gas has likely condensed out of the hot atmosphere. The filament is oriented along the edge of a putative X-ray cavity, suggesting that active galactic nucleus activity has stimulated condensation. This is energetically feasible, although the morphology is not as conclusive as systems whose molecular filaments trail directly behind buoyant radio bubbles. The velocity gradient along the filament is smooth and shallow. It is only consistent with freefall if it lies within 20- of the plane of the sky. The abundance of clusters with comparably low velocities suggests that the filament is not freefalling. Both the central gas and filamentary gas are coincident with bright UV emission from ongoing star formation. Star formation near the cluster core is consistent with the Kennicutt-Schmidt law. The filament exhibits increased star formation surface densities, possibly resulting from either the consumption of a finite molecular gas supply or spatial variations in the CO-to-H2 conversion factor. © 2018. The American Astronomical Society. All rights reserved.
Active galactic nuclei (AGN) release a huge amount of energy into the intracluster medium (ICM) with the consequence of offsetting cooling and star formation (AGN feedback) in the centers of cool core clusters. The Phoenix cluster is among the most massive clusters of galaxies known in the Universe. It hosts a powerful starburst of several hundreds of Solar masses per year and a large amount of molecular gas in the center. In this work we use the high-resolution Reflection Grating Spectrometer (RGS) on board XMM-Newton to study the X-ray emitting cool gas in the Phoenix cluster and heating-cooling balance. We detect for the first time evidence of O VIII and Fe XXI-XXII emission lines, the latter demonstrating the presence of gas below 2 keV. We find a cooling rate of 350 (-200,+250) Msun/year below 2 keV (at the 90% confidence level), which is consistent with the star formation rate in this object. This cooling rate is high enough to produce the molecular gas found in the filaments via instabilities during the buoyant rising time. The line broadening indicates that the turbulence (~ 300 km/s or less) is below the level required to produce and propagate the heat throughout the cool core. This provides a natural explanation to the coexistence of large amounts of cool gas, star formation and a powerful AGN in the core. The AGN activity may be either at a young stage or in a different feedback mode, due to a high accretion rate.
We present a search for nuclear X-ray emission in the Brightest Cluster Galaxies (BCGs) of a sample of groups and clusters of galaxies extracted from the Chandra archive. The exquisite angular resolution of Chandra allows us to obtain robust photometry at the position of the BCG, and to firmly identify unresolved X-ray emission when present, thanks to an accurate characterization of the extended emission at the BCG position. We consider two redshift bins (0.2<z<0.3 and 0.55<z<0.75) and analyze all the clusters observed by Chandra with exposure time larger than 20 ks. Our samples have 81 BCGs in 73 clusters and 51 BCGs in 49 clusters in the low- and high-redshift bin, respectively. X-ray emission in the soft (0.5-2 keV) or hard (2-7 keV) band is detected only in 14 and 9 BCGs ($\sim 18$% of the total samples), respectively. The X-ray photometry shows that at least half of the BCGs have a high hardness ratio, compatible with significant intrinsic absorption. This is confirmed by the spectral analysis with a power law model plus intrinsic absorption. We compute the fraction of X-ray bright BCGs above a given hard X-ray luminosity, considering only sources with positive photometry in the hard band (12/5 sources in the low/high-z sample). In the 0.2<z<0.3 interval the hard X-ray luminosity ranges from $10^{42}$ to $7 \times 10^{43}$ erg s$^{-1}$, with most sources found below $10^{43}$ erg s$^{-1}$. In the $0.55<z<0.75$ range, we find a similar distribution of luminosities below $\sim 10^{44}$ erg s$^{-1}$, plus two very bright sources of a few $10^{45}$ erg s$^{-1}$ associated to two radio galaxies. We also find that X-ray luminous BCGs tend to be hosted by cool core clusters, despite the majority of cool cores do not host nuclear X-ray emission.
We report ALMA Early Science observations of the A1835 brightest cluster galaxy (BCG) in the CO (3-2) and CO (1-0) emission lines. We detect 5 × 1010M
☉ of molecular gas within 10 kpc of the BCG. Its ensemble velocity profile width of ~130 km s–1 FWHM is too narrow for the molecular clouds to be supported in the galaxy by dynamic pressure. The gas may instead be supported in a rotating, turbulent disk oriented nearly face-on. Roughly 1010M
☉ of molecular gas is projected 3-10 kpc to the northwest and to the east of the nucleus with line-of-sight velocities lying between –250 km s–1 and +480 km s–1 with respect to the systemic velocity. The high-velocity gas may be either inflowing or outflowing. However, the absence of high-velocity gas toward the nucleus that would be expected in a steady inflow, and its bipolar distribution on either side of the nucleus, are more naturally explained as outflow. Star formation and radiation from the active galactic nucleus (AGN) are both incapable of driving an outflow of this magnitude. The location of the high-velocity gas projected behind buoyantly rising X-ray cavities and favorable energetics suggest an outflow driven by the radio AGN. If so, the molecular outflow may be associated with a hot outflow on larger scales reported by Kirkpatrick and colleagues. The molecular gas flow rate of approximately 200 M
☉ yr–1 is comparable to the star formation rate of 100-180 M
☉ yr–1 in the central disk. How radio bubbles would lift dense molecular gas in their updrafts, how much gas will be lost to the BCG, and how much will return to fuel future star formation and AGN activity are poorly understood. Our results imply that radio-mechanical (radio-mode) feedback not only heats hot atmospheres surrounding elliptical galaxies and BCGs, but it is able to sweep higher density molecular gas away from their centers.
We present multifrequency observations of the radio galaxy Hydra-A (3C218) located in the core of a massive, X-ray luminous
galaxy cluster. Integral field unit spectroscopy is used to trace the kinematics of the ionized and warm molecular hydrogen
which are consistent with an ∼5 kpc rotating disc. Broad, double-peaked lines of CO(2–1), [C ii] 157 μm and [O i] 63 μm are detected. We estimate the mass of the cold gas within the disc to be Mgas = 2.3 ± 0.3 × 109 M⊙. These observations demonstrate that the complex line profiles found in the cold atomic and molecular gas are related to
the rotating disc or ring of gas. Finally, a Hubble Space Telescope image of the galaxy shows that this gas disc contains a substantial mass of dust. The large gas mass, star formation rate
and kinematics are consistent with the levels of gas cooling from the intracluster medium (ICM). We conclude that the cold
gas originates from the continual quiescent accumulation of cooled ICM gas. The rotation is in a plane perpendicular to the
projected orientation of the radio jets and ICM cavities hinting at a possible connection between the kpc-scale cooling gas
and the accretion of material on to the black hole. We discuss the implications of these observations for models of cold accretion,
AGN feedback and cooling flows.
The radio source 4C 12.50 has often been suggested to be a prime candidate for the link between ultraluminous infrared galaxies and young radio galaxies. A VLBI study of the neutral hydrogen in the nuclear regions of this object shows that most of the gas detected close to the systemic velocity is associated with an off-nuclear cloud (˜ 50 to 100 pc from the radio core) with a column density of ˜ 1022 Tspin/(100 K) cm-2 and an H I mass of a few times 105 to 106 M&sun;. We consider a number of possibilities to explain the results. In particular, we discuss the possibility that this cloud indicates the presence of a rich and clumpy interstellar medium in the centre, likely left over from the merger that triggered the activity and that this medium influences the growth of the radio source. The location of the cloud - at the edge of the northern radio jet/lobe - suggests that the radio jet might be interacting with a gas cloud. This interaction could be responsible for bending the young radio jet. The velocity profile of the gas is relatively broad (˜ 150 km s-1) and we interpret this as kinematical evidence for interaction of the radio plasma with the cloud. We also consider the model where the cloud is part of a broader circumnuclear structure. Only a limited region of this structure would have sufficient background radio brightness and large enough column depth in neutral gas to obtain detectable H I absorption against the counterjet. The VLBI study of the neutral hydrogen in 4C 12.50 suggests that H I detected near the systemic velocity (as it is often the case in radio galaxies) may not necessarily be connected with a circumnuclear disk or torus (as is very often assumed) but instead could be a tracer of the large-scale medium that surrounds the active nucleus and that may influence the growth of the young radio source.
Determining gas content and star formation rate has known remarkable progress
in field galaxies, but has been much less investigated in galaxies inside
clusters. We present the first CO observations of luminous infrared galaxies
(LIRGs) inside the virial radii of two intermediate redshift clusters,
CL1416+4446 (z=0.397) and CL0926+1242 (z=0.489). We detect three galaxies at
high significance (5 to 10 sigma), and provide robust estimates of their CO
luminosities, L'CO. In order to put our results into a general context, we
revisit the relation between cold and hot gas and stellar mass in nearby field
and cluster galaxies. We find evidence that at fixed LIR (or fixed stellar
mass), the frequency of high L'CO galaxies is lower in clusters than in the
field, suggesting environmental depletion of the reservoir of cold gas. The
level of star formation activity in a galaxy is primarily linked to the amount
of cold gas, rather than to the galaxy mass or the lookback time. In clusters,
just as in the field, the conversion between gas and stars seems universal. The
relation between LIR and L'CO for distant cluster galaxies extends the relation
of nearby galaxies to higher IR luminosities. Nevertheless, the intermediate
redshift galaxies fall well within the dispersion of the trend defined by local
systems. Considering that L'CO is generally derived from the CO(1-0) line and
sensitive to the vast majority of the molecular gas in the cold interstellar
medium of galaxies, but less to the part which will actually be used to form
stars, we suggest that molecular gas can be stripped before the star formation
rate is affected. Combining the sample of Geach et al. (2009, 2011) and ours,
we find evidence for a decrease in CO towards the cluster centers. This is the
first hint of an environmental impact on cold gas at intermediate redshift.
The NRAO VLA Sky Survey (NVSS) covers the sky north of J2000.0 delta = -40 deg (82% of the celestial sphere) at 1.4 GHz. The principal data products are (1) a set of 2326 4 deg x 4 deg continuum "cubes'' with three planes containing Stokes I, Q, and U images plus (2) a catalog of almost 2 x 10^6 discrete sources stronger than S ~ 2.5 mJy. The images all have theta = 45" FWHM resolution and nearly uniform sensitivity. Their rms brightness fluctuations are sigma ~ 0.45 mJy beam^-1 ~ 0.14 K (Stokes I) and sigma ~ 0.29 mJy beam^-1 ~ 0.09 K (Stokes Q and U). The rms uncertainties in right ascension and declination vary from <~1" for the N ~ 4 x 10^5 sources stronger than 15 mJy to 7" at the survey limit. The NVSS was made as a service to the astronomical community. All data products, user software, and updates are being released via the World Wide Web as soon as they are produced and verified.
The authors present measurements of the velocity line width, size,
virial mass, and CO luminosity for 273 molecular clouds in the Galactic
disk between longitudes of 8° and 90°. These are obtained from
three-dimensional data in the Massachusetts-Stony Brook CO Galactic
Plane Survey. It is shown that the molecular clouds are in or near
virial equilibrium and are not confined by pressure equilibrium with a
warm or hot phase of interstellar matter. The velocity line width is
proportional to the 0.5 power of the size, σv ∝
S0.5. A tight relationship, over four orders of magnitude, is
found between the cloud dynamical mass, as measured by the virial
theorem, and the CO luminosity M ∝ (LCO)0.81.
The cloud CO luminosity is LCO∝
σv5.
We present the results from the first stage of an optical follow-up study of the X-ray brightest clusters of galaxies detected
in the ROSAT All-Sky Survey (RASS). The redshifts of the central galaxies in 29 of the X-ray brightest Abell and Zwicky clusters in the
RASS have been measured using the Faint Object Spectrograph on the Isaac Newton Telescope. Approximately 40 per cent of the
central galaxy spectra obtained show strong optical line emission. In several cases this emission is quite spectacular. The
central cluster galaxy in Zwicky 3146 is the most luminous such galaxy in optical lines yet discovered, having an Hα luminosity approximately twice that of NGC 1275. We re-examine the link between optical line emission and the presence of
an excess of blue continuum flux in the spectra and find that the two are correlated. The spectral shape of the excess flux
is well matched by B stars.
Some X-ray observations of cooling-flow clusters show soft X-ray
absorption exceeding that expected along the line of sight through our
own Galaxy. This absorption appears at the position of the cooling flow
and covers a similar solid angle at the center of the cluster. The
inferred absorbing column densities correspond to a hydrogen mass
exceeding 1011 Msun, prompting suggestions that
the absorbing material is condensed gas accumulated from the cooling
flow. We explore the characteristics of cold atomic clouds embedded in
an X-ray-emitting cooling flow and find that, if they cover the central
100 kpc of the cluster, they should already have been detected in H I 21
cm emission. Dust in cooling-flow clouds can catalyze molecule
formation, making them unobservable at 21 cm, but dusty molecular clouds
should radiate detectable, optically thick CO rotational lines, which
likewise have not been seen. X-ray transient heating of grains prohibits
most of the CO from condensing onto grain surfaces and thus ensures that
the CO lines are optically thick. Ionized X-ray- absorbing gas would
radiate profusely in optical, UV, or X-ray emission lines. We report
limits on Hα and [Fe X] 6374 Å surface brightnesses from
deep long-slit spectroscopy that rule out ionized columns thicker than
1021 cm-2 and cooler than 1.5 ×
106 K. Limits on 0 VIII Lyα do not allow the
X-ray-absorbing gas to be at higher temperatures.
One remaining possibility is that dust in the hot intracluster medium
absorbs the soft X-rays. The soft X-ray opacity of dust is similar to
its optical opacity. Optical extinctions inferred from the deficits of
background galaxies and quasars counted behind clusters might be
consistent with the dust column densities inferred from soft X-ray
absorption. If dust is the culprit, limits on the 100 microns
luminosities of clusters imply that the dust-to-gas ratio must be higher
at ˜1 Mpc, at which large grains can survive for longer than
109 yr, than in the cores of clusters, where sputtering
destroys grains on a much shorter timescale However, dust at ˜1
Mpc in quantities sufficient to produce significant soft X-ray
absorption represents a large fraction of the total metal content of a
cluster. Submillimeter continuum observations should eventually
determine whether dust is widespread in the intracluster media of
clusters of galaxies.
We observed the brightest central galaxy (BCG) in the nearby (z = 0.0821) cool core galaxy cluster Abell 2597 with the IRAC and MIPS instruments on board the Spitzer Space Telescope. The BCG was clearly detected in all Spitzer bandpasses, including the 70 and 160 μm wave bands. We report aperture photometry of the BCG. The spectral energy distribution exhibits a clear excess in the far-IR over a Rayleigh-Jeans stellar tail, indicating a star formation rate of ~4-5 M☉ yr-1, consistent with the estimates from the UV and its Hα luminosity. This large far-IR luminosity is consistent with that of a starburst or a luminous infrared galaxy, but together with a very massive and old population of stars that dominate the energy output of the galaxy. If the dust is at one temperature, the ratio of 70 to 160 μm fluxes indicates that the dust emitting mid-IR in this source is somewhat hotter than the dust emitting mid-IR in two BCGs at higher redshift (z ~ 0.2-0.3) and higher far-IR luminosities observed earlier by Spitzer in clusters Abell 1835 and Zwicky 3146.
Quillen et al. and O'Dea et al. carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT brightest cluster sample, which were chosen based on their elevated Hα flux. We present Hubble Space Telescope Advanced Camera for Surveys far-ultraviolet (FUV) images of the Lyα and continuum emission of the luminous emission-line nebulae in seven BCGs found to have an infrared (IR) excess. We confirm that the BCGs are actively forming stars which suggests that the IR excess seen in these BCGs is indeed associated with star formation. Our observations are consistent with a scenario in which gas that cools from the intracluster medium fuels the star formation. The FUV continuum emission extends over a region ~7-28 kpc (largest linear size) and even larger in Lyα. The young stellar population required by the FUV observations would produce a significant fraction of the ionizing photons required to power the emission-line nebulae. Star formation rates estimated from the FUV continuum range from ~3 to ~14 times lower than those estimated from the IR, however, both the Balmer decrements in the central few arcseconds and detection of CO in most of these galaxies imply that there are regions of high extinction that could have absorbed much of the FUV continuum. Analysis of archival Very Large Array observations reveals compact radio sources in all seven BCGs and kpc scale jets in A-1835 and RXJ 2129+00. The four galaxies with archival deep Chandra observations exhibit asymmetric X-ray emission, the peaks of which are offset from the center of the BCG by ~10 kpc on average. A low feedback state for the active galactic nucleus could allow increased condensation of the hot gas into the center of the galaxy and the feeding of star formation.
We report new HST NICMOS and WFPC2 imaging of emission-line nebulae in the central galaxies of 3 clusters of galaxies purported to host massive cooling flows, NGC1275, A2597, and PKS0745. The spectral signature of vibrationally- excited molecular hydrogen (VEMH) has been seen in every galaxy searched so far in a cluster cooling flow with an optical emission line nebula. We have discovered that the VEMH gas extends several kpc from the centers of A2597 and PKS0745, while the vibrationally-excited molecular hydrogen in NGC1275 appears to be mostly confined to its nucleus, with some extended emission <1 kpc from the center. The VEMH in A2597 and PKS0745-191 seems to be nearly co-spatial with the optical emission-line filaments in those systems. Candidates for heating the nebulae are X-ray irradiation by the ICM, UV fluorescence by young stars, and shocks. UV heating by young stars provides the most satisfactory explanation for the H2 emission in A2597 and PKS0745; X-ray irradiation is energetically unlikely and strong shocks (v>40 km/s) are ruled out by the high H2/H-alpha ratios. If UV heating is the main energy input, a few billion solar masses of molecular gas is present in A2597 and PKS0745. UV irradiation models predict a significant amount of 1-2 micron emission from higher excitation H2 transitions and moderate far infrared luminosities (~1e44/h^2 erg/s) for A2597 and PKS0745. Even in the context of UV fluorescence models, the total amount of H2 gas and star formation inferred from these observations is too small to account for the cooling flow rates and longevities inferred from the X-rays. We note an interesting new constraint on cooling flow models: the radio sources do not provide a significant amount of shock heating, and therefore cannot counterbalance the cooling of the X-ray gas in the cluster cores.
Quillen et al. presented an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray-luminous clusters. They found that at least half of these sources have signs of excess IR emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-IR emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star-forming galaxies. The gas depletion timescale is about 1 Gyr. The physical extent of the IR excess is consistent with that of the optical emission-line nebulae. This supports the hypothesis that star formation occurs in molecular gas associated with the emission-line nebulae and with evidence that the emission-line nebulae are mainly powered by ongoing star formation. We find a correlation between mass deposition rates () estimated from the X-ray emission and the star formation rates estimated from the IR luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates, suggesting that the reheating of the intracluster medium is generally very effective in reducing the amount of mass cooling from the hot phase but not eliminating it completely.
We report on an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission. These galaxies are located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky Survey. We find that about half of these sources have a sign of excess infrared emission; 22 objects out of 62 are detected at 70 μm, 18 have 8/5.8 μm flux ratios above 1.0 and 28 have 24/8 μm flux ratios above 1.0. Altogether 35 of 62 objects in our survey exhibit at least one of these signs of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 μm flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at 8 μm. Three of these have high measured [O III](5007 Å)/Hβ flux ratios suggesting that these four, Abell 1068, Abell 2146, Zwicky 2089, and R0821+07, host dusty active galactic nuclei (AGNs). Nine objects (including the four hosting dusty AGNs) have infrared luminosities greater than 1011 L☉ and so can be classified as luminous infrared galaxies (LIRGs). Excluding the four systems hosting dusty AGNs, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation.
Star formation within the central galaxies of galaxy clusters is often
interpreted as being fueled by cooling of the hot intracluster medium. However,
the star-forming gas is dusty, and Spitzer spectra show that the dust
properties are similar to those in more normal star-forming environments, in
which the dust has come from the winds of dying stars. Here we consider whether
the primary source of the star-forming gas in central cluster galaxies could be
normal stellar mass loss. We show that the overall stellar mass-loss rate in a
large central galaxy (~4-8 solar masses per year) is at least as large as the
observed star-formation rates in all but the most extreme cases and must be
included in any assessment of the gas-mass budget of a central cluster galaxy.
We also present arguments suggesting that the gas shed by stars in galaxy
clusters with high core pressures and short central cooling times may remain
cool and distinct from its hot surroundings, thereby preserving the dust within
it.
Se presentan resultados recientes de un levantamiento multifrecuencia de
ujos espacialmente resueltos en
galaxias activas cercanas. Se combinan datos espectrosc opicos opticos de Fabry-Perot y de rendija larga con
im agenes del VLA (siglas en ingl es de \Very Large Array") y de ROSAT (siglas en alem an de \Roentgen Satel-
lit"), cuando disponibles, para estudiar las componentes gaseosas tibias, relativistas y calientes involucradas
en el
ujo. Se pone enfasis en objetos que contienen
ujos de angulo amplios y escala gal actica, pero tambi en
que muestran evidencia de fen omenos tipo jet colimado a longitudes de ondas de radio y opticas (p.ej., Circi-
nus, NGC 4388, y con menor intensidad NGC 2992). Nuestros resultados se comparan con las predicciones
publicadas de modelos de vientos t ermicos impulsados por jets.
The brightest cluster galaxy (BCG) in the Abell 1664 cluster is unusually blue and is forming stars at a rate of ~ 23 M_{\sun} yr^{-1}. The BCG is located within 5 kpc of the X-ray peak, where the cooling time of 3.5x10^8 yr and entropy of 10.4 keV cm^2 are consistent with other star-forming BCGs in cooling flow clusters. The center of A1664 has an elongated, "bar-like" X-ray structure whose mass is comparable to the mass of molecular hydrogen, ~ 10^{10} M_{\sun} in the BCG. We show that this gas is unlikely to have been stripped from interloping galaxies. The cooling rate in this region is roughly consistent with the star formation rate, suggesting that the hot gas is condensing onto the BCG. We use the scaling relations of Birzan et al. 2008 to show that the AGN is underpowered compared to the central X-ray cooling luminosity by roughly a factor of three. We suggest that A1664 is experiencing rapid cooling and star formation during a low-state of an AGN feedback cycle that regulates the rates of cooling and star formation. Modeling the emission as a single temperature plasma, we find that the metallicity peaks 100 kpc from the X-ray center, resulting in a central metallicity dip. However, a multi-temperature cooling flow model improves the fit to the X-ray emission and is able to recover the expected, centrally-peaked metallicity profile. Comment: 15 pages, 13 figures
We present 21 cm H I line and 13 cm continuum observations, obtained with the Australian Long Baseline Array, of the Seyfert 2 galaxy IC 5063. This object appears to be one of the best examples of Seyfert galaxies where shocks produced by the radio plasma jet influence both the radio and the near-infrared emission. The picture resulting from the new observations of IC 5063 confirms and completes the one derived from previous Australia Telescope Compact Array (ATCA) lower resolution observations. A strong interaction between the radio plasma ejected from the nucleus and a molecular cloud of the interstellar medium (ISM) is occurring at the position of the western hot spot, about 0.6 kpc from the active nucleus. Because of this interaction, the gas is swept up, forming around the radio lobe a cocoon-like structure where the gas is moving at high speed. Because of this, part of the molecular gas is dissociated and becomes neutral or even ionized if the UV continuum produced by the shocks is hard and powerful enough.
In the 21 cm H I line new data, we detect only part of the strong, blueshifted H I absorption that was previously observed with ATCA at lower resolution. In particular, the main component detected in the VLBI absorption profile corresponds to the most blueshifted component in the ATCA data, with a central velocity of 2786 km s-1 and therefore blueshifted ~614 km s-1 with respect to the systemic velocity. Its peak optical depth is 5.4%. The corresponding column density of the detected absorption, for a spin temperature of 100 K, is NH I ~ 2 × 1021 atoms cm-2. Most of the remaining blueshifted components detected in the ATCA H I absorption profile are now undetected, presumably because this absorption occurs against continuum emission that is resolved out in these high-resolution observations.
The H I absorption properties observed in IC 5063 appear different from those observed in other Seyfert galaxies, where the H I absorption detected is attributed to undisturbed foreground gas associated with the large-scale galaxy disk. In the case of IC 5063, only a small fraction of the absorption can perhaps be due to this. The reason for this could be that the western jet in IC 5063 passes through a particularly rich ISM. Alternatively, because of the relatively strong radio flux produced by this strong interaction and the high spectral dynamic range of our observations, broad absorption lines of low optical depth as detected in IC 5063 may have remained undetected in other Seyfert galaxies that are typically much weaker radio emitters or for which existing data are of poorer quality.
IRAM 30m 12CO(1-0) and 12CO(2-1) HERA observations are presented for the ram-pressure stripped Virgo spiral galaxy NGC 4522. The CO emission is detected in the galactic disk and the extraplanar gas. The extraplanar CO emission follows the morphology of the atomic gas closely but is less extended. The CO maxima do not appear to correspond to regions where there is peak massive star formation as probed by Halpha emission. The presence of molecular gas is a necessary but not sufficient condition for star formation. Compared to the disk gas, the molecular fraction of the extraplanar gas is 30% lower and the star formation efficiency of the extraplanar gas is about 3 times lower. The comparison with an existing dynamical model extended by a recipe for distinguishing between atomic and molecular gas shows that a significant part of the gas is stripped in the form of overdense arm-like structures. It is argued that the molecular fraction depends on the square root of the total large-scale density. Based on the combination of the CO/Halpha and an analytical model, the total gas density is estimated to be about 4 times lower than that of the galactic disk. Molecules and stars form within this dense gas according to the same laws as in the galactic disk, i.e. they mainly depend on the total large-scale gas density. Star formation proceeds where the local large-scale gas density is highest. Given the complex 3D morphology this does not correspond to the peaks in the surface density. In the absence of a confining gravitational potential, the stripped gas arms will most probably disperse; i.e. the density of the gas will decrease and star formation will cease. Comment: 11 pages, 15 figures, A&A accepted for publication
X-ray images and spectra of clusters of galaxies show strong evidence for cooling flows. In many clusters, the hot gas in the core is cooling at rates of ∼ 100M⊙yr−1 and greater. Few traces of the cooled gas have been observed, but it probably forms into low-mass stars (perhaps brown dwarf or even Jupiter-mass objects). X-ray surface-brightness profiles show that the cooling gas is highly inhomogeneous. Overdense gas cools rapidly to form cooled clumps distributed throughout the flow, with little of the gas ever reaching the cluster centre. Cooled and cooling clumps are disrupted because of their motion relative to the remainder of the gas, tending to produce small cooled fragments and, ultimately, low-mass stars. Large molecular clouds, which are the sites of massive star formation in our galaxy, do not occur in the outer parts of cooling flows. There is evidence of larger gas clumps and the formation of more massive stars in the central few kpc of some cooling flows. It is argued that cooling flows efficiently form dark matter. This has wider implications for the formation of dark matter in massive galaxies.
The radio and X-ray properties of a sample of 27 cD galaxies in rich clusters are presented. The radio data consist of 6 cm VLA maps at a resolution of 1-2 arcsec. The X-ray data consist of images and surface-brightness profiles from the Einstein IPC and derived quantities such as cooling times, mass-accretion rates, and thermal pressures from Arnaud (1988). These data are used to explore the relationship between X-ray cooling cores, and the power and morphology of the radio emission. It is found that 71 percent of the cD's with X-ray cooling cores are radio loud, whereas a smaller but still significant 23 percent of cD's without cooling cores are detected at 6 cm above 0.2 mJy. Among the radio galaxies in noncooling core clusters are luminous and extended wide-angle tails. There is a weak correlation between the mass-accretion rate and the radio power for cD's. There is also an interesting class of cooling core cluster (e.g., A2052) with small diameter, amorphous radio emission that may be the result of diffusion along radial magnetic fields set up in cooling inflows. Finally, the relationships between optical emission-line luminosity with radio power and mass-accretion rate are examined. 74 refs.
We examine the detailed physics of the feedback mechanism by relativistic active galactic nucleus (AGN) jets interacting with a two-phase fractal interstellar medium (ISM) in the kpc-scale core of galaxies using 29 three-dimensional grid-based hydrodynamical simulations. The feedback efficiency, as measured by the amount of cloud dispersal generated by the jet-ISM interactions, is sensitive to the maximum size of clouds in the fractal cloud distribution but not to their volume filling factor. Feedback ceases to be efficient for Eddington ratios P{sub jet}/L{sub edd} {approx}< 10{sup -4}, although systems with large cloud complexes {approx}> 50 pc require jets of Eddington ratio in excess of 10{sup -2} to disperse the clouds appreciably. Based on measurements of the bubble expansion rates in our simulations, we argue that sub-grid AGN prescriptions resulting in negative feedback in cosmological simulations without a multi-phase treatment of the ISM are good approximations if the volume filling factor of warm-phase material is less than 0.1 and the cloud complexes are smaller than {approx}25 pc. We find that the acceleration of the dense embedded clouds is provided by the ram pressure of the high-velocity flow through the porous channels of the warm phase, flow that has fully entrained the shocked hot-phase gas it has swept up, and is additionally mass loaded by ablated cloud material. This mechanism transfers 10% to 40% of the jet energy to the cold and warm gas, accelerating it within a few 10 to 100 Myr to velocities that match those observed in a range of high- and low-redshift radio galaxies hosting powerful radio jets.
We present optical integral field spectroscopy of the Hα-luminous (>1042 erg s−1) central cluster galaxies in the cores of the cooling flow clusters A1664, A1835, A2204 and Zw8193. From the [N ii]+Hα complex in these moderate resolution (70–150 km s−1) spectra we derive 2D views of the distribution and kinematics of the emission-line gas, and further diagnostics from the [S ii] and [O i] lines.
The Hα emission shows a variety of disturbed morphologies, ranging from smooth but distorted to clumpy and filamentary, with velocity gradients and splittings of several hundred km s−1 on spatial scales of 20 kpc or more. Despite the small sample size, there are some generic features. The most disturbed Hα emission appears to be associated with secondary galaxies within 10–20 kpc (projected) of the central galaxy and close in velocity to the Hα. The global Hα kinematics match those of the CO(1–0) emission in single-dish data. The [N ii]/Hα, [S ii]/Hα and [O i]/Hα ratios vary little with position, local Hα surface brightness or between clusters.
We propose that the Hα and CO emission arise in molecular clouds heated by a starburst, and that the latter has been triggered by interaction with a secondary galaxy. Such CO emission is known to trace massive (>1010 M⊙) compact (<20 kpc) reservoirs of cool molecular gas, and it is plausible that an infalling galaxy would disturb this gas, distorting the Hα morphology and initiating widespread star formation. We also examine the role of cloud–cloud collisions in the undisturbed molecular gas reservoir, and suggest that they might be an important source of excitation for the emission-line gas in the cores of lower Hα luminosity clusters with less intense star formation.
Cold condensations are inferred to occur throughout X-ray-emitting cooling flows. This paper investigates the physical conditions
within these clouds. Photoionization by the diffuse continuum produced by the surrounding hot gas heats and ionizes the surface
of the cloud to intermediate temperatures (typically 6000 K) and low ionization (the main species present are atomic or singly
ionized). A thermal front occurs at a depth of roughly $6\times10^{15} \ {\rm cm}$ (which corresponds to a hydrogen column density of $\sim 3\times10^{17} \ {\rm cm}^{-2}$), where the conditions change over to those similar to the cold phase of the interstellar medium. The gas within is predominantly
cold (well below 100 K), molecular, and X-ray-heated. Molecular hydrogen forms via ${\rm H}^-$ in the dust-free conditions expected for gas that has rapidly cooled from X-ray-emitting temperatures. The Lyman–Werner bands
of $\rm H_2$ become optically thick, and the hydrogen becomes highly molecular. Eventually, the cloud becomes self-shielded as the result
of a combination of the photoelectric opacity of atomic carbon and Rayleigh scattering, and carbon monoxide forms. Cooling
by rotational transitions of CO brings the temperature of the core of the cloud to that of the cosmic background. We argue
that this is the most likely state of any cloud with sufficient column density to be self-shielded from the diffuse X-ray
continuum. Fragmentation in this core may produce a population of substellar objects.
We present an analysis of sixteen galaxy clusters, one group and one galaxy
drawn from the Chandra X-ray Observatory's data archive. These systems possess
prominent X-ray surface brightness depressions associated with cavities or
bubbles that were created by interactions between powerful radio sources and
the surrounding hot gas. The minimum energy associated with the cavities ranges
between pV~10^55 erg in galaxies, groups, and poor clusters to pV~10^60 erg in
rich clusters. We evaluate the hypothesis that cooling in the hot gas can be
quenched by energy injected into the surrounding gas by the rising bubbles.
Nearly half of the systems in this study may have instantaneous mechanical
luminosities large enough to balance cooling, at least for a short period of
time, if the cavities are filled with a relativistic gas. We find a trend or
upper envelope in the distribution of central X-ray luminosity versus
instantaneous mechanical luminosity with the sense that the most powerful
cavities are found in the most X-ray luminous systems. Such a trend would be
expected if many of these systems produce bubbles at a rate that scales in
proportion to the cooling rate of the surrounding gas. Finally, we use the
X-ray cavities to measure the mechanical power of radio sources over six
decades of radio luminosity, independently of the radio properties themselves.
We find that the ratio of the instantaneous mechanical (kinetic) luminosity to
the 1.4 GHz synchrotron luminosity ranges from a few to roughly a thousand.
This wide range implies that the 1.4 GHz synchrotron luminosity is an
unreliable gauge of the mechanical power of radio sources.
We re-analyse a combined 198 ks Chandra observation of NGC 4696, the brightest galaxy of the Centaurus cluster. We extract temperature and metallicity profiles from
the data, and we confirm the presence of a sharp drop in iron abundance, from ∼1.8 to ∼0.4 Z⊙, within the central 5 kpc of the cluster. We estimate that this central abundance drop corresponds to a total ‘missing’ iron
mass of 1.4 × 106 M⊙. We propose that part of this missing iron is locked up in cool (∼19 K), far-infrared emitting dust, as found by Spitzer and Herschel observations. This can occur if the iron injected by stellar mass-loss in the central region is in grains, which remain in
that form as the injected dusty cold gas mixes and joins the cold dusty filamentary nebula observed within the same region.
The bubbling feedback process observed in the cluster core then drags filaments outward and dumps them at 10–20 kpc radius,
where the metallicity is high.
An analysis based on digital spectroscopy of 3C 33, 98, 184.1, and 218
is presented, which has the objective of discovering whether there is
any correlation between the radio and rotation axes of radio galaxies.
An attempt was made to derive a rotation axis for the stellar as well as
gaseous component of each galaxy. The emission-line measurements reveal
two previously unrecognized characteristics of optical galaxies
associated with double radio sources: they have relatively high internal
rotation velocities, and their rotation axes are nearly aligned with
their radio axes. The slight misalignment found between the two axes for
every object measured, however, appears to be significant and to support
the hypothesis that the radio plasma in such galaxies is ejected along
an axis which is precessing.
We study the consequences of the formation of dust in cold clouds deposited in cooling flows. Such clouds are inferred from
absorption seen in X-ray spectra. Although the gas is initially above 107 K and presumably devoid of dust, we postulate that dust forms in the cold, dense, molecular cores of cooled clouds. If the
dust spreads through the cloud, it causes all but an outer column density of 1020 cm−2 or less of the cloud to be highly molecular and cold (approaching the temperature of the microwave background). Much of the
molecular gas may then freeze out on to the grains. Such dusty cold clouds can then escape detection by current observations
aimed at HI or CO. Either in the very core of the flow where cloud-cloud interactions occur or where a radio source disturbs the clouds,
dusty emission-line and reflection nebulae will be found. Such disturbed regions are relevant to observations of the emission-line
nebulae and excess blue light in cooling flows, the optical alignment effect in distant radio galaxies and the formation of
dust lanes in elliptical galaxies.
A representative sample of 13 dominant cluster galaxies is investigated
to determine the presence of the type of emission-line region seen
around M87 and NGC 1275. Half of the sample shows detectable emission
lines where L(H-alpha + forbidden N III) is greater than 10 to the
40.5th/erg (H0 = 75). The emission-line luminosity appears to
be related to the X-ray luminosity and/or the cluster richness, and a
relationship between optical-line and radio emission is found, which
indicates that the radio source may help form or excite the
emission-line gas. Data are also consistent with the cooling accretion
flow picture, which is modified by including the role of the radio
source.
We have observed 21 elliptical galaxies, of which nine are at the centre of clusters with cooling flows, and find that 12
have extended optical line emission. The spectra show line ratios indicating low ionization and are qualitatively similar
to those observed in other cooling flows. A problem with the production of the large observed line luminosities is highlighted
and explained by some ongoing star formation with the initial mass function of a disc galaxy. The rate of such star formation
is as high as $100{M}_{\odot }\text{yr}^{ \overline{~}1}$ in the case of PKS 0745 – 191, and in all the galaxies there is quantitative agreement between the Hβ line flux and the 4000-Å break measured from our blue spectra. Most of the gas (more than 90 per cent) must cool from X-ray
temperatures and form low-mass objects without producing any detectable optical line radiation or hot young stars.
Components of high-velocity gas have been discovered in the extended emission line regions around two powerful radio galaxies.
The velocity shifts – up to – 1800 km s–1 relative to systemic in the case of 3C405 (Cygnus A) and up to + 1600 km s–1 in the case of 3C265 – are among the largest yet recorded in the extended regions around radio galaxies. In both objects
the shifted components appear to have relatively high ionization states – similar to, or higher than, the unshifted components
of extended ionized gas. The nature of the acceleration mechanism is currently unclear, but it appears most likely that the
large velocity shifts are extreme manifestations of the activity – perhaps the result of interactions between the radio plasma
and the warm or hot interstellar medium.
A 1400 MHz map of the radio source Hydra A with 50-arcsec resolution is
presented which shows that this object is a 3C 31 type source, which is
unusual for an object of such high luminosity. Optical velocity
measurements indicate that the central, optical galaxy consists of a
rapidly rotating core of stars and gas embedded in a nonrotating stellar
envelope. There is also evidence for a region of nonrotating
higher-excitation gas, redshifted relative to the rotating system by
approximately 400 km/s. The position angle of the major axis of the
radio core is shown to be aligned with the optical rotation axis. This
suggests that the more powerful radio sources have their radio structure
more closely aligned with their rotation axes than do the weaker ones;
this implies that the mechanism responsible for the alignment of radio
and rotation axes is related to the radio power of a source and not its
radio morphology.
Charging of dust grains in hot (10,000-1 billion K) plasma is studied,
including photoelectron and secondary electron emission, field emission,
and transmission of electrons and ions through the grain. The resulting
grain potentials are (for temperatures of at least about 100,000 K)
considerably smaller in magnitude than found by Burke and Silk (1974).
Even so, large electrostatic stresses can cause ion field emission and
rapid destruction of small grains in very hot gas. Rapid rotation can
also disrupt small grains, but damping (by microwave emission) usually
limits the centrifugal stress to acceptable values for plasma densities
of no more than about 1 per cu cm. Sputtering rates are estimated for
grains in hot gas, based upon a semiempirical fit to experimental data.
Predicted sputtering rates for possible grain constituents are similar
to estimates by Barlow (1978), but in some cases differ significantly.
Useful approximation formulas are given for the drag forces acting on a
grain with arbitrary Mach number.
CO line emission represents the most accessible and widely used tracer of the
molecular interstellar medium. This renders the translation of observed CO
intensity into total H2 gas mass critical to understand star formation and the
interstellar medium in our Galaxy and beyond. We review the theoretical
underpinning, techniques, and results of efforts to estimate this CO-to-H2
"conversion factor," Xco, in different environments. In the Milky Way disk, we
recommend a conversion factor Xco = 2x10^{20} cm^-2/(K km/s)^-1 with +/-30%
uncertainty. Studies of other "normal galaxies" return similar values in Milky
Way-like disks, but with greater scatter and systematic uncertainty. Departures
from this Galactic conversion factor are both observed and expected. Dust-based
determinations, theoretical arguments, and scaling relations all suggest that
Xco increases with decreasing metallicity, turning up sharply below metallicity
~1/3-1/2 solar in a manner consistent with model predictions that identify
shielding as a key parameter. Based on spectral line modeling and dust
observations, Xco appears to drop in the central, bright regions of some but
not all galaxies, often coincident with regions of bright CO emission and high
stellar surface density. This lower Xco is also present in the overwhelmingly
molecular interstellar medium of starburst galaxies, where several lines of
evidence point to a lower CO-to-H2 conversion factor. At high redshift, direct
evidence regarding the conversion factor remains scarce; we review what is
known based on dynamical modeling and other arguments.
To explain the properties of the most massive low-redshift galaxies and the shape of their mass function, recent models of galaxy evolution include strong AGN feedback to complement starburst-driven feedback in massive galaxies. Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we searched for direct evidence for such feedback in the optical emission line gas around the z = 2.16 powerful radio galaxy MRC 1138-262, likely a massive galaxy in formation. The kiloparsec-scale kinematics, with FWHMs and relative velocities 2400 km s-1 and nearly spherical spatial distribution, do not resemble large-scale gravitational motion or starburst-driven winds. Order-of-magnitude timescale and energy arguments favor the AGN as the only plausible candidate to accelerate the gas, with a total energy injection of a few ×1060 ergs or more, necessary to power the outflow, and relatively efficient coupling between radio jet and ISM. Observed outflow properties are in gross agreement with the models and suggest that AGN winds might have a cosmological significance that is similar to, or perhaps larger than, starburst-driven winds if MRC 1138-262 is indeed archetypal. Moreover, the outflow has the potential to remove significant gas fractions (50%) from a >L* galaxy within a few tens to 100 Myr, fast enough to preserve the observed [α/Fe] overabundance in massive galaxies at low redshift. Using simple arguments, it appears that feedback like that observed in MRC 1138-262 may have sufficient energy to inhibit material from infalling into the dark matter halo and thus regulate galaxy growth as required in some recent models of hierarchical structure formation.
Using broadband optical imaging and Chandra X-ray data for a sample of 46 cluster central dominant galaxies (CDGs), we investigate the connection between star formation, the intracluster medium (ICM), and the central active galactic nucleus (AGN). We report the discovery of a remarkably sharp threshold for the onset of star formation that occurs when the central cooling time of the hot atmosphere falls below ~5 × 108 yr, or equivalently when the central entropy falls below ~30 keV cm2. In addition to this criterion, star formation in cooling flows also appears to require that the X-ray and galaxy centroids lie within ~20 kpc of each other and that the jet (cavity) power is smaller than the X-ray cooling luminosity. These three criteria, together with the high ratio of cooling time to AGN outburst (cavity) age across our sample, directly link the presence of star formation and AGN activity in CDGs to cooling instabilities in the intracluster plasma. Our results provide compelling evidence that AGN feedback into the hot ICM is largely responsible for regulating cooling and star formation in the cores of clusters, leading to the significant growth of supermassive black holes in CDGs at late times.
We present the analysis of the spectroscopic and photometric catalogues of 11 X-ray luminous clusters at 0.07 < z < 0.16 from the Las Campanas/Anglo–Australian Telescope Rich Cluster Survey. Our spectroscopic data set consists of over 1600 galaxy cluster members, of which two-thirds are outside r200. These spectra allow us to assign cluster membership using a detailed mass model and expand on our previous work on the cluster colour–magnitude relation (CMR) where membership was inferred statistically. We confirm that the modal colours of galaxies on the CMR become progressively bluer with increasing radius d(B−R)/drp=−0.011 ± 0.003 and with decreasing local galaxy density d(B−R)/dlog (Σ) =−0.062 ± 0.009. Interpreted as an age effect, we hypothesize that these trends in galaxy colour should be reflected in mean Hδ equivalent width. We confirm that passive galaxies in the cluster increase in Hδ line strength as dHδ/drp= 0.35 ± 0.06. Therefore, those galaxies in the cluster outskirts may have younger luminosity-weighted stellar populations; up to 3 Gyr younger than those in the cluster centre assuming d(B−R)/dt= 0.03 mag per Gyr. A variation of star formation rate, as measured by [O ii]λ3727 Å, with increasing local density of the environment is discernible and is shown to be in broad agreement with previous studies from the 2dF Galaxy Redshift Survey and the Sloan Digital Sky Survey. We divide our spectra into a variety of types based upon the MORPHs classification scheme. We find that clusters at z∼ 0.1 are less active than their higher-redshift analogues: about 60 per cent of the cluster galaxy population is non-star forming, with a further 20 per cent in the post-starburst class and 20 per cent in the currently active class, demonstrating that evolution is visible within the past 2–3 Gyr. We also investigate unusual populations of blue and very red non-star forming galaxies and we suggest that the former are likely to be the progenitors of galaxies which will lie on the CMR, while the colours of the latter possibly reflect dust reddening. We show that the cluster galaxies at large radii consist of both backsplash ones and those that are infalling to the cluster for the first time. We make a comparison to the field population at z∼ 0.1 and examine the broad differences between the two populations. Individually, the clusters show significant variation in their galaxy populations which we suggest reflects their recent infall histories.
Brightest cluster galaxies (BCGs) in the cores of galaxy clusters have distinctly different properties from other low-redshift massive ellipticals. The majority of the BCGs in cool-core clusters show signs of active star formation. We present observations of NGC 4696, the BCG of the Centaurus galaxy cluster, at far-infrared (FIR) wavelengths with the Herschel space telescope. Using the PACS spectrometer, we detect the two strongest coolants of the interstellar medium, [C ii] at 157.74 μm and [O i] at 63.18 μm, and in addition [N ii] at 121.90 μm. The [C ii] emission is extended over a region of 7 kpc with a similar spatial morphology and kinematics to the optical Hα emission. This has the profound implication that the optical hydrogen recombination line, Hα, the optical forbidden lines, [N ii] λ6583 Å, the soft X-ray filaments and the FIR [C ii] line all have the same energy source.
We also detect dust emission using the PACS and SPIRE photometers at all six wavebands. We perform a detailed spectral energy distribution fitting using a two-component modified blackbody function and find a cold 19-K dust component with mass 1.6 × 106 M⊙ and a warm 46-K dust component with mass 4.0 × 103 M⊙. The total FIR luminosity between 8 and 1000 μm is 7.5 × 108 L⊙, which using Kennicutt relation yields a low star formation rate of 0.13 M⊙ yr−1. This value is consistent with values derived from other tracers, such as ultraviolet emission. Combining the spectroscopic and photometric results together with optical Hα, we model emitting clouds consisting of photodissociation regions adjacent to ionized regions. We show that in addition to old and young stellar populations, there is another source of energy, such as cosmic rays, shocks or reconnection diffusion, required to excite the Hα and [C ii] filaments.
We present the detections of CO line emission in the central galaxy of 16 extreme cooling flow clusters using the IRAM 30-m and the JCMT 15-m telescopes. These detections of , , and are consistent with the presence of a substantial mass of warm molecular gas within 50-kpc radius of the central galaxy. We present limits on 13 other galaxies in similarly extreme cooling flow clusters. These results are consistent with the presence of a massive starburst in the central galaxy, which warms a population of cold gas clouds producing both optical and near-infrared emission lines and significant CO line emission. Curiously, our CO detections are restricted to the lower radio power central galaxies. These are the first detections of molecular gas in a cooling flow other than NGC 1275 in the Perseus cluster. As four of our targets have firm limits on their dust mass from SCUBA and the rest have crude limits from IRAS, we can calculate gas-to-dust ratios. Simple analysis indicates that the best secondary indicator of molecular gas is optical line luminosity. We review the implications of these results and the prospects for observations in the near future.
We present the first detection of CO emission lines in the Halpha filaments
at distances as far as 50 kpc from the centre of the galaxy NGC 1275. This gas
is probably dense (>=10E3 cm-3). However, it is not possible to accurately
determine the density and the kinetic temperature of this relatively warm gas
(Tkin~20-500K) with the current data only. The amount of molecular gas in the
filaments is large 10E9 Msun (assuming a Galactic N(H2)/Ico ratio). This is 10%
of the total mass of molecular gas detected in this cD galaxy. This gas has
large-scale velocities comparable to those seen in Halpha. The origin of the
filaments is still unclear, but their formation is very likely linked to the
AGN positive feedback (Revaz et al., 2008) that regulates the cooling of the
surrounding X-ray-emitting gas as suggested by numerical simulations. We also
present high-resolution spectra of the galaxy core. The spatial characteristics
of the double-peaked profile suggest that the molecular web of filaments and
streamers penetrates down to radii of less than 2 kpc from the central AGN and
eventually feed the galaxy nucleus. The mass of gas inside the very central
region is ~10E^9 Msun, and is similar to the mass of molecular gas found in the
filaments.
We have carried out a survey for 12CO J=1-0 and J=2-1 emission in the 260
early-type galaxies of the volume-limited Atlas3D sample, with the goal of
connecting their star formation and assembly histories to their cold gas
content. This is the largest volume-limited CO survey of its kind and is the
first to include many Virgo Cluster members. Sample members are dynamically hot
galaxies with a median stellar mass 3\times 10^{10} Msun; they are selected by
morphology rather than colour, and the bulk of them lie on the red sequence.
The overall CO detection rate is 56/259 = 0.22 \error 0.03, with no dependence
on K luminosity and only a modest dependence on dynamical mass. There are a
dozen CO detections among the Virgo Cluster members; statistical analysis of
their H_2 mass distributions and their dynamical status within the cluster
shows that the cluster's influence on their molecular masses is subtle at best,
even though (unlike spirals) they seem to be virialized within the cluster. We
suggest that the cluster members have retained their molecular gas through
several Gyr residences in the cluster. There are also a few extremely CO-rich
early-type galaxies with H_2 masses >= 10^9 Msun, and these are in low density
environments. We do find a significant trend between molecular content and the
stellar specific angular momentum. The galaxies of low angular momentum also
have low CO detection rates, suggesting that their formation processes were
more effective at destroying molecular gas or preventing its re-accretion. We
speculate on the implications of these data for the formation of various
sub-classes of early-type galaxies.
We investigate the effect of three important processes by which AGN-blown bubbles transport material: drift, wake transport and entrainment. The first of these, drift, occurs because a buoyant bubble pushes aside the adjacent material, giving rise to a net upward displacement of the fluid behind the bubble. For a spherical bubble, the mass of upwardly displaced material is roughly equal to half the mass displaced by the bubble, and should be ~ 10^{7-9} solar masses depending on the local ICM and bubble parameters. We show that in classical cool core clusters, the upward displacement by drift may be a key process in explaining the presence of filaments behind bubbles. A bubble also carries a parcel of material in a region at its rear, known as the wake. The mass of the wake is comparable to the drift mass and increases the average density of the bubble, trapping it closer to the cluster centre and reducing the amount of heating it can do during its ascent. Moreover, material dropping out of the wake will also contribute to the trailing filaments. Mass transport by the bubble wake can effectively prevent the build-up of cool material in the central galaxy, even if AGN heating does not balance ICM cooling. Finally, we consider entrainment, the process by which ambient material is incorporated into the bubble. Abridged Comment: Accepted for publication in MNRAS. 17 pages, 4 figures, 2 tables. Formatted for letter paper and adjusted author affiliations.
[Abridged] Photoionization, whether by starlight or other sources, has difficulty in accounting for the observed spectra of the optical filaments that often surround central galaxies in large clusters. Our first paper examined whether heating by energetic particles or dissipative MHD wave can account for the observations. Here we include atomic and low-ionization regions. The model of the hydrogen atom, along with all elements of the H-like iso-electronic sequence, is now fully nl-resolved. We show how the predicted HI spectrum differs from the pure recombination case. The second update is to the rates for H^0 - H2 inelastic collisions. We now use the values computed by Wrathmall et al. The rates are often much larger. We calculate the chemistry, ionization, temperature, gas pressure, and emission-line spectrum for a wide range of gas densities and collisional heating rates. We assume that the filaments are magnetically confined and free to move along field lines so that the gas pressure is equal to that of the surrounding hot gas. A mix of clouds, some being dense and cold and others hot and tenuous, can exist. The observed spectrum will be the integrated emission from clouds with different densities and temperatures but the same pressure. We assume that the gas filling factor is given by a power law in density. The power-law index is set by matching the observed intensities of IR H2 lines relative to optical HI lines. We conclude that the filaments are heated by ionizing particles, either conducted in from surrounding regions or produced in situ by processes related to MHD waves.
We present aperture synthesis images of the CO (1-0) line emission in five central galaxies in cooling flow clusters using the Owens Valley Millimeter Array. Three of the five sources are significantly resolved, but the majority of the emission is from a compact (<20 kpc) region centered on the central galaxy. These results are consistent with the newly emerging view that cooling flows deposit much less gas over a shorter period in a smaller volume than previously thought. The size constraints derived imply that the molecular gas has a large (>1022 cm-2) column density. We review the implications of these results and the prospects for observations in the near future.
We present VLT-SINFONIK-band integral field spectroscopy of the central galaxies in the cool core clusters A1664, A2204 and PKS 0745−191, to probe the spatio-kinematic properties of the Paα and ro-vibrational H2 line emission.
In A1664, the two emission-line velocity systems seen in our previous Hα spectroscopy appear in both Paα and H2 emission, with notable morphological differences. The recession velocity of the red component of Paα increases linearly with decreasing radius, particularly along an 8 kpc filament aligned with the major axis of the underlying galaxy and the cluster X-ray emission. These kinematics are modelled as gravitational free-fall as gas cools rapidly out of the hot phase. In A2204, the gas shows three or four filaments reaching radii of 10 kpc, three of which lie towards ‘ghost bubbles’ seen in X-ray imaging by Sanders et al. For PKS 0745−191, we confirm the twin-arm morphology in the narrow-band images of Donahue et al.; the Paα kinematics suggest rotational motion about an axis aligned with the kiloparsec-scale radio jet; on nucleus, we find an underlying broad Paα component [full width at half-maximum (FWHM) 1700 km s−1] and a secondary H2 velocity system redshifted by +500 km s−1.
The H2 v= 1−0 S(3)/Paα ratio is the highest in the most isolated and extended regions where it matches the levels in the NGC 1275 filaments as modelled by Ferland et al. Regions with much lower ratios highlight active star formation and are often kinematically quiescent (FWHM < 200 km s−1). Our findings suggest that the three clusters may be captured in different stages of the ‘cold feedback’ cycle of Pizzolato & Soker, with A1664 in a short-lived phase of extreme cooling and star formation prior to an active galactic nucleus (AGN) heating event; PKS 0745−191 in an outburst state with the AGN accreting from a cool gas disc, and A2204 in a later phase in which cool gas is dragged out of the galaxy by the buoyant rise of old radio bubbles.
The results of long-slit spectroscopy obtained for the core regions of 14 clusters of galaxies are reported. The data are presented in detail. It is shown that the presence of optical emission is tied to the properties of the hot gas in the cluster and not to the morphology of the central galaxy or cluster, demonstrating that the optical systems are indeed formed by the cooling of hot gas. Cooling flows occur when the gas density exceeds a critical central value which corresponds to a cooling time scale which, it is argued, weakly favors low values of H(0). The kinematics of the gas flows are discussed. The excitation mechanisms, correlation of optical emission with radio properties, and upper limits on coronal line strengths from the hot gas are discussed.
The results of a two-dimensional spectrophotometric survey of the core regions of 11 rich clusters of galaxies are presented. A number of these clusters have spectacular optical emission line systems in their cores. Both morphologically and kinematically, the emission line regions divide into extended, 20-100 kpc systems of long linear filaments associated with the cluster core and more compact, homogeneous elongated regions associated with the dominant central cluster galaxy. It is suggested that the present results can be expected, as hot X-ray emitting gas cools in the cluster center. Luminosities almost entirely agree with expected values. The morphology of the systems can be understood if the filaments form initially in the cooling flow and, in some cases, are subsequently accreted by the central galaxy.
We use simple analytic reasoning to identify physical processes that drive the evolution of the cosmic star formation rate, , in cold dark matter universes. Based on our analysis, we formulate a model to characterize the redshift dependence of and compare it with results obtained from a set of hydrodynamic simulations that include star formation and feedback.
We find that the cosmic star formation rate is described by two regimes. At early times, densities are sufficiently high and cooling times sufficiently short that abundant quantities of star-forming gas are present in all dark matter haloes that can cool by atomic processes. Consequently, generically rises exponentially as z decreases, independent of the details of the physical model for star formation, but dependent on the normalization and shape of the cosmological power spectrum. This part of the evolution is dominated by gravitationally driven growth of the halo mass function. At low redshifts, densities decline as the universe expands to the point that cooling is inhibited, limiting the amount of star-forming gas available. We find that in this regime the star formation rate scales approximately as , in proportion to the cooling rate within haloes.
We demonstrate that the existence of these two regimes leads to a peak in the star formation rate at an intermediate redshift z=zpeak. We discuss how the location of this peak depends on our model parameters, and show that the peak cannot occur above a limiting redshift of z≈ 8.7. For the star formation efficiency adopted in our numerical simulations, zpeak≈ 5–6, with half of all stars forming at redshifts larger than z≃ 2.2.
We derive analytic expressions for the full star formation history and show that they match our simulation results to better than ≃10 per cent. Using various approximations, we reduce the expressions to a simple analytic fitting function for that can be used to compute global cosmological quantities that are directly related to the star formation history. As examples, we consider the integrated stellar density, the supernova and gamma-ray burst rates observable on Earth, the metal enrichment history of the Universe, and the density of compact objects. We also briefly discuss the expected dependence of the star formation history on cosmological parameters and the physics of the gas.
The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the observations, the survey has a much lower resolution in declination than in right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS shows that the positional accuracy is less constrained in declination than in right ascension, but there is no significant systematic error. We present a source list containing 73570 sources. We correlate this WISH catalogue with the NVSS to construct a sample of faint Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies with large optical telescopes in the southern hemisphere. This sample is aimed at increasing the number of known high redshift radio galaxies to allow detailed follow-up studies of these massive galaxies and their environments in the early Universe. Comment: 12 Pages, including 5 PostScript figures. Accepted for publication in Astronomy & Astrophysics. The full WISH catalog with 73570 sources is available from http://www.strw.leidenuniv.nl/wenss/