S. Veilleux

Leiden University, Leyden, South Holland, Netherlands

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Publications (269)1055.26 Total impact

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    ABSTRACT: The under-abundance of very massive galaxies in the Universe is frequently attributed to the effect of galactic winds. Although ionized galactic winds are readily observable, most of the expelled mass (that is, the total mass flowing out from the nuclear region) is likely to be in atomic and molecular phases that are cooler than the ionized phases. Expanding molecular shells observed in starburst systems such as NGC 253 (ref. 12) and M 82 (refs 13, 14) may facilitate the entrainment of molecular gas in the wind. Although shell properties are well constrained, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution better than 100 parsecs coupled with sensitivity to a wide range of spatial scales, a combination hitherto not available. Here we report observations of NGC 253, a nearby starburst galaxy (distance ∼ 3.4 megaparsecs) known to possess a wind, that trace the cool molecular wind at 50-parsec resolution. At this resolution, the extraplanar molecular gas closely tracks the Hα filaments, and it appears to be connected to expanding molecular shells located in the starburst region. These observations allow us to determine that the molecular outflow rate is greater than 3 solar masses per year and probably about 9 solar masses per year. This implies a ratio of mass-outflow rate to star-formation rate of at least 1, and probably ∼3, indicating that the starburst-driven wind limits the star-formation activity and the final stellar content.
    Nature 07/2013; 499(7459):450-3. · 38.60 Impact Factor
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    ABSTRACT: Recent observations have shown the presence of dust and molecular material in galactic winds, but relatively little is known about the distribution of these outflow components. To shed some light on this issue, we have used IRAC images from the Spitzer Space Telescope archive to investigate polycyclic aromatic hydrocarbon (PAH) emission from a sample of 16 local galaxies with known winds. Our focus on nearby sources (median distance 8.6 Mpc) has revealed detailed PAH structure in the winds and allowed us to measure extraplanar PAH emission. We have identified extraplanar PAH features on scales of ~ 0.8 - 6.0 kpc. We find a nearly linear correlation between the amount of extraplanar PAH emission and the total infrared flux, a proxy for star formation activity in the disk. Our results also indicate a correlation between the height of extraplanar PAH emission and star formation rate surface density, which supports the idea of a surface density threshold on the energy or momentum injection rate for producing detectable extraplanar wind material.
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    ABSTRACT: The under-abundance of very massive galaxies in the universe is frequently attributed to the effect of galactic winds. Although ionized galactic winds are readily observable most of the expelled mass is likely in cooler atomic and molecular phases. Expanding molecular shells observed in starburst systems such as NGC 253 and M 82 may facilitate the entrainment of molecular gas in the wind. While shell properties are well constrained, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution <100 pc coupled with sensitivity to a wide range of spatial scales, hitherto not available. Here we report observations of NGC 253, a nearby starburst galaxy (D~3.4 Mpc) known to possess a wind, which trace the cool molecular wind at 50 pc resolution. At this resolution the extraplanar molecular gas closely tracks the H{\alpha} filaments, and it appears connected to molecular expanding shells located in the starburst region. These observations allow us to directly measure the molecular outflow rate to be > 3 Msun/yr and likely ~9 Msun/yr. This implies a ratio of mass-outflow rate to star formation rate of at least {\eta}~1-3, establishing the importance of the starburst-driven wind in limiting the star formation activity and the final stellar content.
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    ABSTRACT: We present the first results of a survey of the [CII]158um emission line in 241 luminous infrared galaxies (LIRGs) comprising the Great Observatories All-sky Survey (GOALS) sample, obtained with the PACS instrument on board Herschel. The [CII] luminosities of the LIRGs in GOALS range from ~10^7 to 2x10^9 Lsun. We find that LIRGs show a tight correlation of [CII]/FIR with far-IR flux density ratios, with a strong negative trend spanning from ~10^-2 to 10^-4, as the average temperature of dust increases. We find correlations between the [CII]/FIR ratio and the strength of the 9.7um silicate absorption feature as well as with the luminosity surface density of the mid-IR emitting region (Sigma_MIR), suggesting that warmer, more compact starbursts have substantially smaller [CII]/FIR ratios. Pure star-forming (SF) LIRGs have a mean [CII]/FIR ~ 4x10^-3, while galaxies with low 6.2um PAH equivalent widths (EWs), indicative of the presence of active galactic nuclei (AGN), span the full range in [CII]/FIR. However, we show that even when only pure SF galaxies are considered, the [CII]/FIR ratio drops by an order of magnitude, from 10^-2 to 10^-3, with Sigma_MIR and Sigma_IR, implying that the [CII] luminosity is not a good indicator of the star formation rate (SFR) for most LIRGs, for it does not scale linearly with the warm dust emission. Moreover, even in LIRGs in which we detect an AGN in the mid-IR, the majority (2/3) of galaxies show [CII]/FIR >= 10^-3 typical of high 6.2um PAH EW sources, suggesting that most AGNs do not contribute significantly to the far-IR emission. We provide an empirical relation between the [CII]/FIR and the specific SFR (SSFR) for SF LIRGs. Finally, we present predictions for the starburst size based on the observed [CII] and far-IR luminosities which should be useful for comparing with results from future surveys of high-redshift galaxies with ALMA and CCAT.
    The Astrophysical Journal 07/2013; 774(1). · 6.73 Impact Factor
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    Kory Kreimeyer, Sylvain Veilleux
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    ABSTRACT: We report the discovery of giant ionization cones in the 140-kpc nebula around quasar MR 2251-178 based on deep [O III] 5007/H-beta and [N II] 6583/H-alpha flux ratio maps obtained with the Maryland-Magellan Tunable Filter (MMTF) on the Baade-Magellan 6.5m telescope. These cones are aligned with the weak double-lobed radio source observed on smaller scale <30 kpc). They have an opening angle ~120deg +/- 10deg and subtend ~65-90% of 4pi steradians, where the large uncertainty takes into account possible projection effects. The material in the outer ionization cones is matter-bounded, indicating that all ionizing photons emitted through the cones escape from the system. The quasar ionizing flux is ~2-3 times fainter outside of these cones, despite the largely symmetric geometry of the nebula in [O III]. Overall, adding up the contributions from both inside and outside the cones, we find that ~65-95% of the quasar ionizing radiation makes its way out of the system. These results emphasize the need for line ratio maps to quantify the escape fraction of ionizing radiation from quasars and the importance of quasar radiative feedback on the intergalactic medium.
    The Astrophysical Journal Letters 06/2013; 772(1). · 6.35 Impact Factor
  • David S. N. Rupke, Sylvain Veilleux
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    ABSTRACT: Massive, galaxy-scale outflows are known to be ubiquitous in major mergers of disk galaxies in the local universe. In this paper, we explore the multiphase structure and power sources of galactic winds in six ultraluminous infrared galaxies (ULIRGs) at z < 0.06 using deep integral field spectroscopy with the Gemini Multi-Object Spectrograph (GMOS) on Gemini North. We probe the neutral, ionized, and dusty gas phases using Na I D, strong emission lines ([O I], Hα, and [N II]), and continuum colors, respectively. We separate outflow motions from those due to rotation and tidal perturbations, and find that all of the galaxies in our sample host high-velocity flows on kiloparsec scales. The properties of these outflows are consistent with multiphase (ionized, neutral, and dusty) collimated bipolar winds emerging along the minor axis of the nuclear disk to scales of 1-2 kpc. In two cases, these collimated winds take the form of bipolar superbubbles, identified by clear kinematic signatures. Less collimated (but still high-velocity) flows are also present on scales up to 5 kpc in most systems. The three galaxies in our sample with obscured QSOs host higher velocity outflows than those in the three galaxies with no evidence for an active galactic nucleus. The peak outflow velocity in each of the QSOs is in the range 1450-3350 km s–1, and the highest velocities (2000-3000 km s–1) are seen only in ionized gas. The outflow energy and momentum in the QSOs are difficult to produce from a starburst alone, but are consistent with the QSO contributing significantly to the driving of the flow. Finally, when all gas phases are accounted for, the outflows are massive enough to provide negative feedback to star formation.
    The Astrophysical Journal 04/2013; 768(1):75. · 6.73 Impact Factor
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    ABSTRACT: The Great Observatories All-Sky LIRG Survey (GOALS) is a multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer spectra covering 5-38um and provide a basic analysis of the mid-IR spectral properties for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra. The GOALS sample of 244 nuclei in 180 luminous and 22 ultraluminous IR galaxies represents a complete subset of the IRAS RBGS and covers a range of merger stages, morphologies and spectral types. The majority (>60%) of GOALS LIRGs have high 6.2um PAH equivalent widths (EQW > 0.4um) and low levels of silicate absorption (s_9.7um >-1.0). There is a general trend among the U/LIRGs for silicate depth and MIR slope to increase with LIR. U/LIRGs in the late stages of a merger also have on average steeper MIR slopes and higher levels of dust obscuration. Together these trends suggest that as gas & dust is funneled towards the center of a coalescing merger, the nuclei become more compact and obscured. The sources that depart from these correlations have very low PAH EQW (EQW < 0.1um) consistent with their MIR emission being dominated by an AGN. The most heavily dust obscured sources are the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst. As the merger progresses a marked decline is seen for the fraction of high EQW (star formation dominated) sources while the fraction of composite sources increases but the fraction of AGN-dominated sources remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z~2, the average GOALS LIRG is more absorbed at 9.7um and has more PAH emission. However, when the AGN contributions to both the local LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starbursting SMGs.
    The Astrophysical Journal Supplement Series 02/2013; 206(1). · 16.24 Impact Factor
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    ABSTRACT: We present the first analysis of the all-sky Swift BAT ultra hard X-ray (14-195 keV) data for a targeted list of objects. We find the BAT data can be studied at 3x fainter limits than in previous blind detection catalogs based on prior knowledge of source positions and using smaller energy ranges for source detection. We determine the AGN fraction in 134 nearby (z<0.05) luminous infrared galaxies (LIRGS) from the GOALS sample. We find that LIRGs have a higher detection frequency than galaxies matched in stellar mass and redshift at 14-195 keV and 24-35 keV. In agreement with work at other wavelengths, the AGN detection fraction increases strongly at high IR luminosity with half of high luminosity LIRGs (50%, 6/12, log L_IR/L_sun>11.8) detected. The BAT AGN classification shows 97% (37/38) agreement with Chandra and XMM AGN classification using hardness ratios or detection of a iron K-alpha line. This confirms our statistical analysis and supports the use of the Swift BAT all-sky survey to study fainter populations of any category of sources in the ultra hard X-ray band. BAT AGN in LIRGs tend to show higher column densities with 40\pm9% showing 14-195 keV/2-10 keV hardness flux ratios suggestive of high or Compton-thick column densities (log N_H>24 cm^-2), compared to only 12\pm5% of non-LIRG BAT AGN. We also find that using specific energy ranges of the BAT detector can yield additional sources over total band detections with 24% (5/21) of detections in LIRGs at 24-35 keV not detected at 14-195 keV.
    The Astrophysical Journal Letters 02/2013; 765(2). · 6.35 Impact Factor
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    Stacy H. Teng, Sylvain Veilleux, Andrew J. Baker
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    ABSTRACT: We present the results of a 21-cm HI survey of 27 local massive gas-rich late-stage mergers and merger remnants with the Robert C. Byrd Green Bank Telescope (GBT). These remnants were selected from the Quasar/ULIRG Evolution Study (QUEST) sample of ultraluminous infrared galaxies (ULIRGs; L$_{8-1000 \mu m} > 10^{12}$ L$_\odot$) and quasars; our targets are all bolometrically dominated by active galactic nuclei (AGN) and sample the later phases of the proposed ULIRG-to-quasar evolutionary sequence. We find the prevalence of HI absorption (emission) to be 100% (29%) in ULIRGs with HI detections, 100% (88%) in FIR-strong quasars, and 63% (100%) in FIR-weak quasars. The absorption features are associated with powerful neutral outflows that change from being mainly driven by star formation in ULIRGs to being driven by the AGN in the quasars. These outflows have velocities that exceed 1500 km s$^{-1}$ in some cases. Unexpectedly, we find polarization-dependent HI absorption in 57% of our spectra (88% and 63% of the FIR-strong and FIR-weak quasars, respectively). We attribute this result to absorption of polarized continuum emission from these sources by foreground HI clouds. About 60% of the quasars displaying polarized spectra are radio-loud, far higher than the $\sim$10% observed in the general AGN population. This discrepancy suggests that radio jets play an important role in shaping the environments in these galaxies. These systems may represent a transition phase in the evolution of gas-rich mergers into "mature" radio galaxies.
    The Astrophysical Journal 01/2013; 765(2). · 6.73 Impact Factor
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    ABSTRACT: Massive stars strongly influence the properties of their interstellar and intergalactic environments through radiative feedback. The resulting HII regions are used as diagnostics for many galaxy properties, and the radiation from massive stars is thought to be a source for reionization in the early universe. Yet, there are still unanswered questions about the shape of the massive star spectral energy distribution and how far the radiation propagates in a galaxy. We use the emission-line spectra of a sample of single-star HII regions, in conjunction with photoionization simulations, to evaluate the predictions of widely used stellar atmosphere models. The model atmospheres generate simulated HII region spectra that agree well with the observations, except at the highest energy transitions, provided that the nebular density distributions are inhomogeneous. WM-basic atmospheres are better at reproducing the observed nebular spectrum, while TLUSTY atmospheres more closely match the observed rate of ionizing photons. Based on the results of our detailed CLOUDY simulations, we create a new spectral type to stellar effective temperature calibration. We also investigate the galactic parameters that control the propagation of ionizing radiation out of a galaxy by searching for extended, photoionized emission in a sample of nearby, dwarf starburst galaxies. Using narrowband emission-line images taken with the Maryland-Magellan Tunable Filter, we create ionization parameter maps of the starbursts. In NGC 5253, we detect an optically thin ionization cone extending from the central starburst, which is suggestive of the escape of ionizing radiation. The narrow morphology of the cone supports the scenario that an orientation bias contributes to the challenge of detecting Lyman continuum in starbursts and Lyman Break Galaxies.
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    ABSTRACT: We present the first results of ALMA cycle 0 observations of NGC 253, the nearest nuclear starburst galaxy. The observations consist of two parts: (1) a 7-point low-resolution mosaic in the CO(1-0) line of the nuclear starburst and its surroundings and (2) a 3-point high-resolution mosaic of the high density tracers HCN and HCO+. The data show clear evidence for molecular gas entrained in the prominent outflow emerging from the central starburst. This is the first time molecular gas is seen in the outflow of NGC 253, a superwind which to date has been studied mainly through through deep H-alpha and X-ray imaging. The high-resolution imaging of the dense gas tracers at the base of the superwind resolve the giant molecular clouds (GMCs) that give rise to the high star formation efficiency of the nuclear starburst. Within the wide bandwidth of the ALMA observations we identify an additional ~25 molecular lines in the central region that trace shocks, dense gas, and optically thin lines such as C17O, H13CO+ and HN13C. The wealth of available data give new key insights into the mechanisms that trigger the central starburst and drive the outflow in NGC 253.
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    ABSTRACT: The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, is opening up the high energy X-ray sky to sensitive study for the first time. Its combination of continuous spectral coverage over the 3-79 keV bandpass, low background and high sensitivity make NuSTAR the ideal instrument with which to enhance our understanding of the population of highly obscured active galactic nuclei (AGN), and the nature of their absorbing structures. NuSTAR will undertake two complimentary observational approaches for these sources. First, a few key objects covering three distinct obscuration regimes (borderline Compton thick: NH ~ 1e24, moderately Compton thick: 1e24 < NH < 1e25 and heavily Compton thick: NH > 1e25 at/cm^2) will be studied with long, high S/N observations in order to investigate in detail the reprocessed ('reflected') emission from the obscuring medium. Second, a series of snapshot overvations with more moderate S/N will be performed for a larger sample of ~30 spectroscopically identified Compton thick AGN, selected from mega-maser, Swift BAT and mid-IR samples, in order to investigate the evolution of the obscuring medium with various key physical quantities, e.g. inclination, intrinsic luminosity, etc. Here, we discuss plans, predictions and early results of the NuSTAR obscured AGN program.
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    ABSTRACT: Mrk 231, the nearest (z = 0.0422) quasar, hosts both a galactic-scale wind and a nuclear-scale iron low-ionization broad absorption line (FeLoBAL) outflow. We recently obtained a far-ultraviolet (FUV) spectrum of this object covering ~1150 - 1470 A with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. This spectrum is highly peculiar, highlighted by the presence of faint (~< 2% of predictions based on H-alpha), broad (>~ 10,000 km/s at the base), and highly blueshifted (centroid at ~ -3500 km/s) Ly-alpha emission. The FUV continuum emission is slightly declining at shorter wavelengths (consistent with F_lambda ~ lambda^1.7) and does not show the presence of any obvious photospheric or wind stellar features. Surprisingly, the FUV spectrum also does not show any unambiguous broad absorption features. It thus appears to be dominated by the AGN, rather than hot stars, and virtually unfiltered by the dusty FeLoBAL screen. The observed Ly-alpha emission is best explained if it is produced in the outflowing BAL cloud system, while the Balmer lines arise primarily from the standard broad emission line region seen through the dusty (A_V ~ 7 mag.) broad absorption line region. Two possible geometric models are discussed in the context of these new results.
    The Astrophysical Journal 12/2012; 764(1). · 6.73 Impact Factor
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    ABSTRACT: We present the first scientific results from the Sydney-AAO Multi-Object IFS (SAMI) at the Anglo-Australian Telescope. This unique instrument deploys 13 fused fibre bundles (hexabundles) across a one-degree field of view allowing simultaneous spatially-resolved spectroscopy of 13 galaxies. During the first SAMI commissioning run, targeting a single galaxy field, one object (ESO 185-G031) was found to have extended minor axis emission with ionisation and kinematic properties consistent with a large-scale galactic wind. The importance of this result is two-fold: (i) fibre bundle spectrographs are able to identify low-surface brightness emission arising from extranuclear activity; (ii) such activity may be more common than presently assumed because conventional multi-object spectrographs use single-aperture fibres and spectra from these are nearly always dominated by nuclear emission. These early results demonstrate the extraordinary potential of multi-object hexabundle spectroscopy in future galaxy surveys.
    The Astrophysical Journal 12/2012; 761(2):169. · 6.73 Impact Factor
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    ABSTRACT: We present Hubble Space Telescope Wide Field Camera 3 observations of the core of the Phoenix Cluster SPT-CLJ2344-4243 in five broadband filters spanning rest-frame 1000--5500A. These observations reveal complex, filamentary blue emission, extending for >40kpc from the brightest cluster galaxy. We observe an underlying, diffuse population of old stars, following an r^1/4 distribution, confirming that this system is somewhat relaxed. The spectral energy distribution in the inner part of the galaxy, as well as along the extended filaments, is a smooth continuum and is consistent with that of a star-forming galaxy, suggesting that the extended, filamentary emission is not due to the central AGN, either from a large-scale ionized outflow or scattered polarized UV emission, but rather a massive population of young stars. We estimate an extinction-corrected star formation rate of 798 +/- 42 Msun/yr, consistent with our earlier work based on low spatial resolution ultraviolet, optical, and infrared imaging. The lack of tidal features and multiple bulges, combine with the need for an exceptionally massive (>10^11 Msun) cold gas reservoir, suggest that this star formation is not the result of a merger of gas-rich galaxies. Instead, we propose that the high X-ray cooling rate of ~2700 Msun/yr is the origin of the cold gas reservoir. The combination of such a high cooling rate and the relatively weak radio source in the cluster core suggests that feedback has been unable to halt cooling in this system, leading to this tremendous burst of star formation.
    The Astrophysical Journal Letters 11/2012; 765(2). · 6.35 Impact Factor
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    ABSTRACT: We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J=4-3 through J=13-12, 6 H2O rotational lines, and [CI] and [NII] fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H2 v=1-0 S(1) and v=2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity v_s=10 km s^-1 and a pre-shock density n_H=5 * 10^4 cm^-3. We find that the solution best fitting the H2 lines is degenerate: The shock velocities and number densities range between v_s = 17 - 47 km s^-1 and n_H=10^7 - 5 * 10^4 cm^-3, respectively. The H2 lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s^-1) shocks while only a small fraction (< 1 percent) of the ISM is exposed to the high velocity shocks. This implies that the gas is rapidly loosing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.
    The Astrophysical Journal Letters 11/2012; 762(2). · 6.35 Impact Factor
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    ABSTRACT: We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at least 285 and \sim200 K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5-1)x10^{16} cm-2 and \sim2x10^{-8}, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+\sim5-10. H3O+ is detected in both sources with N(H3O+)\sim(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ~500 K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is zeta>10^{-13} s-1, a lower limit that is severalx10^2 times the highest rate estimates for Galactic regions. In Arp 220, our lower limit for zeta is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an AGN is responsible for the molecular ion production.
    Astronomy and Astrophysics 11/2012; · 5.08 Impact Factor
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    ABSTRACT: [Abridged] We present maps of the main cooling lines of the neutral atomic gas ([OI] at 63 and 145 micron and [CII] at 158 micron) and in the [OIII] 88 micron line of the starburst galaxy M82, carried out with the PACS spectrometer on board the Herschel satellite. By applying PDR modeling we derive maps of the main ISM physical parameters, including the [CII] optical depth, at unprecedented spatial resolution (~300 pc). We can clearly kinematically separate the disk from the outflow in all lines. The [CII] and [OI] distributions are consistent with PDR emission both in the disk and in the outflow. Surprisingly, in the outflow, the atomic and the ionized gas traced by the [OIII] line both have a deprojected velocity of ~75 km/s, very similar to the average velocity of the outflowing cold molecular gas (~ 100 km/s) and several times smaller than the outflowing material detected in Halpha (~ 600 km/s). This suggests that the cold molecular and neutral atomic gas and the ionized gas traced by the [OIII] 88 micron line are dynamically coupled to each other but decoupled from the Halpha emitting gas. We propose a scenario where cold clouds from the disk are entrained into the outflow by the winds where they likely evaporate, surviving as small, fairly dense cloudlets (n_H\sim 500-1000 cm^-3, G_0\sim 500- 1000, T_gas\sim300 K). We show that the UV photons provided by the starburst are sufficient to excite the PDR shells around the molecular cores. The mass of the neutral atomic gas in the outflow is \gtrsim 5-12x 10^7 M_sun to be compared with that of the molecular gas (3.3 x 10^8 M_sun) and of the Halpha emitting gas (5.8 x 10^6 M_sun). The mass loading factor, (dM/dt)/SFR, of the molecular plus neutral atomic gas in the outflow is ~ 2. Energy and momentum driven outflow models can explain the data equally well, if all the outflowing gas components are taken into account.
    Astronomy and Astrophysics 10/2012; · 5.08 Impact Factor
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    ABSTRACT: In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous 'cooling flows' of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates and cool gas masses for these 'cool-core' clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2 × 10(45) erg s(-1)) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.
    Nature 08/2012; 488(7411):349-52. · 38.60 Impact Factor
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    ABSTRACT: Results of observations with the Spitzer, Hubble, GALEX, Chandra, and XMM-Newton space telescopes are presented for the Luminous Infrared Galaxy (LIRG) merger Mrk 266. The SW (Seyfert 2) and NE (LINER) nuclei reside in galaxies with Hubble types SBb (pec) and S0/a (pec), respectively. Both galaxies have L > L*, and they are inferred to each contain a ~2.5x10^8 M_sun black hole. Mrk 266 SW is likely the primary source of a bright Fe K-alpha line detected from the system, consistent with the reflection-dominated X-ray spectrum of a heavily obscured AGN. Optical knots embedded in an arc with aligned radio continuum radiation, combined with luminous H_2 line emission, provide evidence for a radiative bow shock in an AGN-driven outflow surrounding the NE nucleus. Soft X-ray emission modeled as shock-heated plasma is co-spatial with radio continuum emission between the galaxies. Mid-IR diagnostics indicate roughly equal contributions of AGN and starburst radiation powering the bolometric luminosity. Approximately 120 star clusters have been detected, with most having estimated ages < 50 Myr. Detection of 24 micron emission extending ~34 arcsec (20 kpc) north of the galaxies is interpreted as ~2x10^7 M_sun of dust entrained in an outflowing superwind; at optical wavelengths this region is resolved into a fragmented morphology indicative of Rayleigh-Taylor instabilities in an expanding shell of ionized gas. Mrk 266 demonstrates that the dust "blow-out" phase can begin in a LIRG well before the galaxies fully coalesce during a subsequent ULIRG phase, and rapid gas consumption in luminous dual AGNs (kpc scale separations) early in the merger process may explain the paucity of detected binary QSOs (sub-pc scale orbits) in large surveys. An evolutionary sequence is proposed representing a progression from dual to binary AGNs, accompanied by an increase in observed L_x/L_ir ratios by 10^4 or more.
    The Astronomical Journal 08/2012; 144(5). · 4.97 Impact Factor

Publication Stats

4k Citations
1,055.26 Total Impact Points


  • 2014
    • Leiden University
      • Leiden Observartory
      Leyden, South Holland, Netherlands
  • 2013–2014
    • The Space Science Institute
      Boulder, Colorado, United States
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 1991–2014
    • University of California, Santa Cruz
      Santa Cruz, California, United States
    • University of Alabama
      Tuscaloosa, Alabama, United States
  • 1970–2014
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, United States
  • 2002–2013
    • California Institute of Technology
      • • Department of Astronomy
      • • Spitzer Science Center
      Pasadena, California, United States
  • 1998–2013
    • Honolulu University
      Honolulu, Hawaii, United States
  • 2012
    • University of Chicago
      • Kavli Institute for Cosmological Physics
      Chicago, Illinois, United States
    • University of Sydney
      • Sydney Institute of Astronomy (SIfA)
      Sydney, New South Wales, Australia
    • National Academy of Sciences of Armenia
      • Byurakan Astrophysical Observatory
      Ayrivan, Yerevan, Armenia
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2011
    • University of Oregon
      • Department of Physics
      Eugene, OR, United States
  • 2010
    • Stony Brook University
      • Department of Physics and Astronomy
      Stony Brook, NY, United States
  • 2009
    • Dickinson College
      Carlisle, Pennsylvania, United States
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
  • 2003–2008
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, Maryland, United States
  • 2007
    • University of Maryland, Baltimore
      Baltimore, Maryland, United States
  • 2005
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, Maryland, United States
  • 1999–2002
    • Loyola University Maryland
      Baltimore, Maryland, United States
    • University of California, Berkeley
      Berkeley, California, United States
  • 1993
    • Rice University
      Houston, Texas, United States