P. Tozzi

Beijing Normal University, Peping, Beijing, China

Are you P. Tozzi?

Claim your profile

Publications (250)718.96 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We perform a comprehensive study of the total mass distribution of the galaxy cluster RXCJ2248 ($z=0.348$) with a set of high-precision strong lensing models, which take advantage of extensive spectroscopic information on many multiply lensed systems. In the effort to understand and quantify inherent systematics in parametric strong lensing modelling, we explore a collection of 22 models where we use different samples of multiple image families, parametrizations of the mass distribution and cosmological parameters. As input information for the strong lensing models, we use the CLASH HST imaging data and spectroscopic follow-up observations, carried out with the VIMOS and MUSE spectrographs, to identify bona-fide multiple images. A total of 16 background sources, over the redshift range $1.0-6.1$, are multiply lensed into 47 images, 24 of which are spectroscopically confirmed and belong to 10 individual sources. The cluster total mass distribution and underlying cosmology in the models are optimized by matching the observed positions of the multiple images on the lens plane. We show that with a careful selection of a sample of spectroscopically confirmed multiple images, the best-fit model reproduces their observed positions with a rms of $0.3$ in a fixed flat $\Lambda$CDM cosmology, whereas the lack of spectroscopic information lead to biases in the values of the model parameters. Allowing cosmological parameters to vary together with the cluster parameters, we find (at $68\%$ confidence level) $\Omega_m=0.25^{+0.13}_{-0.16}$ and $w=-1.07^{+0.16}_{-0.42}$ for a flat $\Lambda$CDM model, and $\Omega_m=0.31^{+0.12}_{-0.13}$ and $\Omega_\Lambda=0.38^{+0.38}_{-0.27}$ for a universe with $w=-1$ and free curvature. Using toy models mimicking the overall configuration of RXCJ2248, we estimate the impact of the line of sight mass structure on the positional rms to be $0.3\pm 0.1$.(ABRIDGED)
    No preview · Article · Dec 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the dust-obscured star formation (SF) properties of the massive, X-ray-selected galaxy cluster MACS J1931.8−2634 at z = 0.352. Using far-infrared (FIR) imaging in the range 100–500 μm obtained with the Herschel telescope, we extract 31 sources (2σ) within r ∼ 1 Mpc from the brightest cluster galaxy (BCG). Among these sources, we identify six cluster members for which we perform an analysis of their spectral energy distributions (SEDs). We measure total infrared luminosity (LIR), star formation rate (SFR) and dust temperature. The BCG, with LIR = 1.4 × 1012 L⊙ is an ultraluminous infrared galaxy and hosts a type-II active galactic nuclei (AGN). We decompose its FIR SED into AGN and starburst components and find equal contributions from AGN and starburst. We also recompute the SFR of the BCG finding SFR = 150 ± 15 M⊙ yr−1. We search for an isobaric cooling flow in the cool core using Chandra X-ray data, and find no evidence for gas colder than 1.8 keV in the inner 30 kpc, for an upper limit to the instantaneous mass-deposition rate of 58 M⊙ yr−1 at 95 per cent c.l. This value is 3× lower than the SFR in the BCG, suggesting that the on-going SF episode lasts longer than the intracluster medium cooling events.
    Preview · Article · Nov 2015 · Monthly Notices of the Royal Astronomical Society Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present VIMOS-VLT spectroscopy of the Frontier Fields cluster MACS~J0416.1-2403. Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts, including ~800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to ~3$r_{200}$ (~5Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster ($M_{200}$~0.9$\times 10^{15} M_{\odot}$) presenting two major features: i) a bimodal velocity distribution, showing two central peaks separated by $\Delta V_{rf}$~1100 km s$^{-1}$ with comparable galaxy content and velocity dispersion, ii) a projected elongation of the main substructures along the NE-SW direction, with a prominent subclump ~600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low mass structure at z~0.390, ~10' S of the cluster center, projected at ~3Mpc, with a relative line-of-sight velocity of $\Delta V_{rf}$~-1700 km s$^{-1}$. The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the "universal" NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal overall a complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in line with recent findings from radio and deep X-ray data. With this article we also release the entire redshift catalog of 4386 sources in the field of this cluster.
    No preview · Article · Nov 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the ionization and kinematics of the ionized gas in the nuclear region of the barred Seyfert 2 galaxy NGC~5643 using MUSE integral field observations in the framework of the MAGNUM (Measuring Active Galactic Nuclei Under MUSE Microscope) survey. The data were used to identify regions with different ionization conditions and to map the gas density and the dust extinction. We find evidence for a double sided ionization cone, possibly collimated by a dusty structure surrounding the nucleus. At the center of the ionization cone, outflowing ionized gas is revealed as a blueshifted, asymmetric wing of the [OIII] emission line, up to projected velocity v(10)~-450 km/s. The outflow is also seen as a diffuse, low luminosity radio and X-ray jet, with similar extension. The outflowing material points in the direction of two clumps characterized by prominent line emission with spectra typical of HII regions, located at the edge of the dust lane of the bar. We propose that the star formation in the clumps is due to `positive feedback' induced by gas compression by the nuclear outflow, providing the first candidate for outflow induced star formation in a Seyfert-like radio quiet AGN. This suggests that positive feedback may be a relevant mechanism in shaping the black hole-host galaxy coevolution.
    Preview · Article · Aug 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the star formation properties of ∼800 sources detected in one of the deepest radio surveys at 1.4 GHz. Our sample spans a wide redshift range (∼0.1–4) and about four orders of magnitude in star formation rate (SFR). It includes both star-forming galaxies (SFGs) and active galactic nuclei (AGNs), further divided into radio-quiet (RQ) and radio-loud objects. We compare the SFR derived from the far-infrared luminosity, as traced by Herschel, with the SFR computed from their radio emission. We find that the radio power is a good SFR tracer not only for pure SFGs but also in the host galaxies of RQ AGNs, with no significant deviation with redshift or specific SFR. Moreover, we quantify the contribution of the starburst activity in the SFG population and the occurrence of AGNs in sources with different level of star formation. Finally, we discuss the possibility of using deep radio survey as a tool to study the cosmic star formation history.
    Preview · Article · Aug 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    Ang Liu · Heng Yu · Paolo Tozzi · Zong-Hong Zhu
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose a strategy to search for bulk motions in the intracluster medium (ICM) of merging clusters based on {\sl Chandra} CCD data. Our goal is to derive robust measurements of the average redshift of projected ICM regions obtained from the centroid of the $K_\alpha$ line emission. We thoroughly explore the effect of the unknown temperature structure along the line of sight to accurately evaluate the systematic uncertainties on the ICM redshift. We apply our method to the "Bullet cluster" (1E~0657-56). We directly identify 23 independent regions on the basis of the surface brightness contours, and measure the redshift of the ICM averaged along the line of sight in each. We find that the redshift distribution across these regions is marginally inconsistent with the null hypothesis of a constant redshift or no bulk motion in the ICM, at a confidence level of about $2\, \sigma$. We tentatively identify the regions most likely affected by bulk motions and find a maximum velocity gradient of about $(46\pm 13)$ $\rm km~s^{-1}~kpc^{-1}$ along the line of sight on a scale of $\sim 260 $ kpc along the path of the "bullet." We interpret this as the possible signature of a significant mass of ICM pushed away along a direction perpendicular to the merging. This preliminary result is promising for a systematic search for bulk motions in bright, moderate-redshift clusters based on spatially resolved spectral analysis of {\sl Chandra} CCD data. This preliminary result is promising for a systematic search for bulk motions in bright, moderate-redshift clusters based on spatially resolved spectral analysis of {\sl Chandra} CCD data.
    Preview · Article · Aug 2015 · The Astrophysical Journal
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Aims. In the effort to understand the link between the structure of galaxy clusters and their galaxy populations, we focus on MACS J1206.2-0847 at z ~ 0.44 and probe its substructure in the projected phase space through the spectrophotometric properties of a large number of galaxies from the CLASH-VLT survey. Methods. Our analysis is mainly based on an extensive spectroscopic dataset of 445 member galaxies, mostly acquired with VIMOS at VLT as part of our ESO Large Programme, sampling the cluster out to a radius ~2R_(200) (4 h_(70)^(-1) Mpc). We classify 412 galaxies as passive, with strong Hδ absorption (red and blue galaxies), and with emission lines from weak to very strong. A number of tests for substructure detection are applied to analyze the galaxy distribution in the velocity space, in 2D space, and in 3D projected phase-space. Results. Studied in its entirety, the cluster appears as a large-scale relaxed system with a few secondary, minor overdensities in 2D distribution. We detect no velocity gradients or evidence of deviations in local mean velocities. The main feature is the WNW-ESE elongation. The analysis of galaxy populations per spectral class highlights a more complex scenario. The passive galaxies and red strong Hδ galaxies trace the cluster center and the WNW-ESE elongated structure. The red strong Hδ galaxies also mark a secondary, dense peak ~2 h_(70)^(-1) Mpcat ESE. The emission line galaxies cluster in several loose structures, mostly outside R_(200). Two of these structures are also detected through our 3D analysis. The observational scenario agrees with MACS J1206.2-0847 having WNW-ESE as the direction of the main cluster accretion, traced by passive galaxies and red strong Hδ galaxies. The red strong Hδ galaxies, interpreted as poststarburst galaxies, date a likely important event 1−2 Gyr before the epoch of observation. The emission line galaxies trace a secondary, ongoing infall where groups are accreted along several directions.
    Full-text · Article · Jul 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the Extended Chandra Deep Field-South Very Large Array sample, which reaches a flux density limit at 1.4 GHz of 32.5 μJy at the field centre and redshift ∼4, and covers ∼0.3 deg2. Number counts are presented for the whole sample while the evolutionary properties and luminosity functions are derived for active galactic nuclei (AGN). The faint radio sky contains two totally distinct AGN populations, characterized by very different evolutions, luminosity functions, and Eddington ratios: radio-quiet (RQ)/radiative-mode and radio-loud (RL)/jet-mode AGN. The radio power of RQ AGN evolves $\mathrel {{\rlap{{\lower4pt{\sim }}}{\propto }}}(1+z)^{2.5}$, similarly to star-forming galaxies, while the number density of RL ones has a peak at z ∼ 0.5 and then declines at higher redshifts. The number density of radio-selected RQ AGN is consistent with that of X-ray selected AGN, which shows that we are sampling the same population. The unbiased fraction of radiative-mode RL AGN, derived from our own and previously published data, is a strong function of radio power, decreasing from ∼0.5 at P1.4 GHz ∼ 1024 W Hz−1 to ∼0.04 at P1.4 GHz ∼ 1022 W Hz−1. Thanks to our enlarged sample, which now includes ∼700 radio sources, we also confirm and strengthen our previous results on the source population of the faint radio sky: star-forming galaxies start to dominate the radio sky only below ∼0.1 mJy, which is also where RQ AGN overtake RL ones.
    Full-text · Article · Jun 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: (Abridged) We present a spectral analysis of a deep (220 ks) XMM-Newton observation of the Phoenix cluster (SPT-CL J2344-4243), which we also combine with Chandra archival ACIS-I data. We extract CCD and RGS X-ray spectra from the core region to search for the signature of cold gas, and constrain the mass deposition rate in the cooling flow which is thought to be responsible of the massive star formation episode observed in the BCG. We find an average mass deposition rate of $\dot M = 620 (-190 +200)_{stat} (-50 +150)_{syst} M_\odot$/yr in the temperature range 0.3-3.0 keV from MOS data. A temperature-resolved analysis shows that a significant amount of gas is deposited only above 1.8 keV, while upper limits of the order of hundreds of $M_\odot$/yr can be put in the 0.3-1.8 keV temperature range. From pn data we obtain $\dot M = 210 (-80 +85)_{stat} ( -35 +60)_{syst} M_\odot$/yr, and the upper limits from the temperature-resolved analysis are typically a factor of 3 lower than MOS data. In the RGS spectrum, no line emission from ionization states below Fe XXIII is seen above $12 \AA$, and the amount of gas cooling below $\sim 3$ keV has a best-fit value $\dot M = 122_{-122}^{+343}$ $M_{\odot}$/yr. In addition, our analysis of the FIR SED of the BCG based on Herschel data provides $SFR = (530 \pm 50) M_\odot$/yr, significantly lower than previous estimates by a factor 1.5. Current data are able to firmly identify substantial amount of cooling gas only above 1.8 keV in the core of the Phoenix cluster. While MOS data analysis is consistent with values as high as $\dot M \sim 1000$ within $1 \sigma$, pn data provide $\dot M < 500 M_\odot$ yr$^{-1}$ at $3\sigma$ c.l. at temperature below 1.8 keV. At present, this discrepancy cannot be explained on the basis of known calibration uncertainties or other sources of statistical noise.
    Full-text · Article · May 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the combined analysis of the metal content of 83 objects in the redshift range 0.09-1.39, and spatially-resolved in the 3 bins (0-0.15, 0.15-0.4, >0.4) R500, as obtained with similar analysis using XMM-Newton data in Leccardi & Molendi (2008) and Baldi et al. (2012). We use the pseudo-entropy ratio to separate the Cool-Core (CC) cluster population, where the central gas density tends to be relatively higher, cooler and more metal rich, from the Non-Cool-Core systems. The average, redshift-independent, metal abundance measured in the 3 radial bins decrease moving outwards, with a mean metallicity in the core that is even 3 (two) times higher than the value of 0.16 times the solar abundance in Anders & Grevesse (1989) estimated at r>0.4 R500 in CC (NCC) objects. We find that the values of the emission-weighted metallicity are well-fitted by the relation $Z(z) = Z_0 (1+z)^{-\gamma}$ at given radius. A significant scatter, intrinsic to the observed distribution and of the order of 0.05-0.15, is observed below 0.4 R500. The nominal best-fit value of $\gamma$ is significantly different from zero in the inner cluster regions ($\gamma = 1.6 \pm 0.2$) and in CC clusters only. These results are confirmed also with a bootstrap analysis, which provides a still significant negative evolution in the core of CC systems (P>99.9 per cent). No redshift-evolution is observed when regions above the core (r > 0.15 R500) are considered. A reasonable good fit of both the radial and redshift dependence is provided from the functional form $Z(r,z)=Z_0 (1+(r/0.15 R500)^2)^{-\beta} (1+z)^{-\gamma}$, with $(Z_0, \beta, \gamma) = (0.83 \pm 0.13, 0.55 \pm 0.07, 1.7 \pm 0.6)$ in CC clusters and $(0.39 \pm 0.04, 0.37 \pm 0.15, 0.5 \pm 0.5)$ for NCC systems. Our results represent the most extensive study of the spatially-resolved metal distribution in the cluster plasma as function of redshift.
    Full-text · Article · Apr 2015 · Astronomy and Astrophysics
  • [Show abstract] [Hide abstract]
    ABSTRACT: Aims. We present the detection, identification and calibration of extended sources in the deepest X-ray dataset to date, the Extended Chandra Deep Field South (ECDF-S). Methods. Ultra-deep observations of ECDF-S with Chandra and XMM-Newton enable a search for extended X-ray emission down to an unprecedented flux of 2 × 10^(-16) ergs s^(-1) cm^(-2). By using simulations and comparing them with the Chandra and XMM data, we show that it is feasible to probe extended sources of this flux level, which is 10 000 times fainter than the first X-ray group catalogs of the ROSAT all sky survey. Extensive spectroscopic surveys at the VLT and Magellan have been completed, providing spectroscopic identification of galaxy groups to high redshifts. Furthermore, available HST imaging enables a weak-lensing calibration of the group masses. Results. We present the search for the extended emission on spatial scales of 32′′ in both Chandra and XMM data, covering 0.3 square degrees and model the extended emission on scales of arcminutes. We present a catalog of 46 spectroscopically identified groups, reaching a redshift of 1.6. We show that the statistical properties of ECDF-S, such as log N − log S and X-ray luminosity function are broadly consistent with LCDM, with the exception that dn/dz/dΩ test reveals that a redshift range of 0.2 < z < 0.5 in ECDF-S is sparsely populated. The lack of nearby structure, however, makes studies of high-redshift groups particularly easier both in X-rays and lensing, due to a lower level of clustered foreground. We present one and two point statistics of the galaxy groups as well as weak-lensing analysis to show that the detected low-luminosity systems are indeed low-mass systems. We verify the applicability of the scaling relations between the X-ray luminosity and the total mass of the group, derived for the COSMOS survey to lower masses and higher redshifts probed by ECDF-S by means of stacked weak lensing and clustering analysis, constraining any possible departures to be within 30% in mass. Conclusions. Ultra-deep X-ray surveys uniquely probe the low-mass galaxy groups across a broad range of redshifts. These groups constitute the most common environment for galaxy evolution. Together with the exquisite data set available in the best studied part of the Universe, the ECDF-S group catalog presented here has an exceptional legacy value.
    No preview · Article · Apr 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the Swift X-ray Cluster Survey (SWXCS) catalog obtained using archival data from the X-ray telescope (XRT) on board the Swift satellite acquired from 2005 to 2012, extending the first release of the SWXCS. The catalog provides positions, soft fluxes, and, when possible, optical counterparts for a flux-limited sample of X-ray group and cluster candidates. We consider the fields with Galactic latitude |b| > 20 degree to avoid high HI column densities. We discard all of the observations targeted at groups or clusters of galaxies, as well as particular extragalactic fields not suitable to search for faint extended sources. We finally select ~3000 useful fields covering a total solid angle of ~400 degree^2. We identify extended source candidates in the soft-band (0.5-2keV) images of these fields using the software EXSdetect, which is specifically calibrated for the XRT data. Extensive simulations are used to evaluate contamination and completeness as a function of the source signal, allowing us to minimize the number of spurious detections and to robustly assess the selection function. Our catalog includes 263 candidate galaxy clusters and groups down to a flux limit of 7E-15 erg/cm^2/s in the soft band, and the logN-logS is in very good agreement with previous deep X-ray surveys. The final list of sources is cross-correlated with published optical, X-ray, and SZ catalogs of clusters. We find that 137 sources have been previously identified as clusters, while 126 are new detections. Currently, we have collected redshift information for 158 sources (60% of the entire sample). Once the optical follow-up and the X-ray spectral analysis of the sources are complete, the SWXCS will provide a large and well-defined catalog of groups and clusters of galaxies to perform statistical studies of cluster properties and tests of cosmological models.
    Preview · Article · Mar 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract]
    ABSTRACT: Aims. In the effort to understand the link between the structure of galaxy clusters and their galaxy populations, we focus on MACSJ1206.2-0847, at z ∼ 0.44, probing its substructure in the projected phase space through the spectrophotometric properties of a large number of galaxies from the CLASH-VLT survey. Methods. Our analysis is mainly based on an extensive spectroscopic dataset of 445 member galaxies, mostly acquired with VIMOS@VLT as part of our ESO Large Programme, sampling the cluster out to a radius ∼ 2R200 (4 h−1 70 Mpc). We classify 412 galaxies as: passive, with strong Hδ absorption (red and blue ones), and with emission lines from weak to very strong ones. A number of tests for substructure detection is applied to analyze the galaxy distribution in the velocity space, in the 2D space, and in the (3D) projected phase-space. Results. Studied in its entirety, the cluster appears as a large-scale relaxed system with a few, secondary, minor overdensities in 2D distribution. We detect no velocity gradient or evidence of deviations in local mean velocities. The main feature is the WNW-ESE elongation. The analysis of galaxy populations per spectral class highlights a more complex scenario. The passive and red strong Hδ galaxies trace the cluster center and the WNW-ESE elongated structure. The red strong Hδ galaxies also mark a secondary, dense peak ∼ 2 h−1 70 Mpc at ESE. The emission line galaxies cluster in several loose structures, mostly outside R200. Two of these structures are also detected through our 3D analysis. The observational scenario agrees with MACS J1206.2-0847 having WNW-ESE as the direction of the main cluster accretion, traced by passive and red strong Hδ galaxies. The latter ones, interpreted as poststarburst galaxies, date a likely important event 1-2 Gyr before the epoch of observation. The emission line galaxies trace a secondary, ongoing infall where groups are accreted along several directions.
    No preview · Article · Mar 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ultra-deep observations of ECDF-S with Chandra and XMM-Newton enable a search for extended X-ray emission down to an unprecedented flux of $2\times10^{-16}$ ergs s$^{-1}$ cm$^{-2}$. We present the search for the extended emission on spatial scales of 32$^{\prime\prime}$ in both Chandra and XMM data, covering 0.3 square degrees and model the extended emission on scales of arcminutes. We present a catalog of 46 spectroscopically identified groups, reaching a redshift of 1.6. We show that the statistical properties of ECDF-S, such as logN-logS and X-ray luminosity function are broadly consistent with LCDM, with the exception that dn/dz/d$\Omega$ test reveals that a redshift range of $0.2<z<0.5$ in ECDF-S is sparsely populated. The lack of nearby structure, however, makes studies of high-redshift groups particularly easier both in X-rays and lensing, due to a lower level of clustered foreground. We present one and two point statistics of the galaxy groups as well as weak-lensing analysis to show that the detected low-luminosity systems are indeed low-mass systems. We verify the applicability of the scaling relations between the X-ray luminosity and the total mass of the group, derived for the COSMOS survey to lower masses and higher redshifts probed by ECDF-S by means of stacked weak lensing and clustering analysis, constraining any possible departures to be within 30\% in mass. Abridged.
    Full-text · Article · Jan 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In about 70% of the population of relaxed, cool-core galaxy clusters, the brightest cluster galaxy (BCG) is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). In recent years such relativistic plasma has been unambiguously shown to interact with the surrounding thermal intra-cluster medium (ICM) thanks to spectacular images where the lobe radio emission is observed to fill the cavities in the X-ray-emitting gas. This `radio feedback' phenomenon is widespread and is critical to understand the physics of the inner regions of galaxy clusters and the properties of the central BCG. At the same time, mechanically-powerful AGN are likely to drive turbulence in the central ICM which may also play a role for the origin of non-thermal emission on cluster-scales. Diffuse non-thermal emission has been observed in a number of cool-core clusters in the form of a radio mini-halo surrounding the radio-loud BCG on scales comparable to that of the cooling region. Large mini-halo samples are necessary to establish their origin and connection with the cluster thermal properties and dynamics, especially in light of future X-ray characterization of the cluster cores as it is expected by Athena-XIFU. We show that All-Sky reference survey at Band 2 with SKA1 at confusion limit (rms ~2 {\mu}Jy per beam) has the potential to detect up to ~620 mini-halos at redshift z<0.6, whereas Deep Tier reference surveys at Band 1/2 with SKA1 at sub-arcsec resolution (rms ~0.2 {\mu}Jy per beam) will allow a complete census of the radio-loud BCGs at any redshift down to a 1.4 GHz power of 10^{22} W/Hz. We further anticipate that SKA2 might detect up to ~1900 new mini-halos at redshift z<0.6 and characterize the radio-mode AGN feedback in every cluster and group up to redshift z ~1.7 (the highest-z where virialized clusters are currently detected).
    Full-text · Article · Dec 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the analysis of the Chandra observation of XDCP J0044.0-2033, a massive, distant (z=1.579) galaxy cluster discovered in the XDCP survey. The total exposure time of 380 ks with Chandra ACIS-S provides the deepest X-ray observation currently achieved on a massive, high redshift cluster. Extended emission from the Intra Cluster Medium (ICM) is detected at a very high significance level (S/N~20) on a circular region with a 44" radius, corresponding to $R_{ext}=375$ kpc at the cluster redshift. We perform an X-ray spectral fit of the ICM emission modeling the spectrum with a single-temperature thermal mekal model. Our analysis provides a global temperature $kT=6.7^{+1.3}_{-0.9}$ keV, and a iron abundance $Z_{Fe} = 0.41_{-0.26}^{+0.29}Z_{Fe_\odot}$ (error bars correspond to 1 $\sigma$). We fit the background-subtracted surface brightness profile with a single $\beta$-model out to 44", finding a rather flat profile with no hints of a cool core. We derive the deprojected electron density profile and compute the ICM mass within the extraction radius $R_{ext}=375$ kpc to be $M_{ICM}(r<R_{ext}) = (1.48 \pm 0.20) \times 10^{13} M_\odot$. Under the assumption of hydrostatic equilibrium and assuming isothermality within $R_{ext}$, the total mass is $M_{2500}= 1.23_{-0.27}^{+0.46} \times 10 ^{14} M_\odot$ for $R_{2500} = 240_{-20}^{+30}$ kpc. Extrapolating the profile at radii larger than the extraction radius $R_{ext}$ we find $M_{500} = 3.2_{-0.6}^{+0.9} \times 10 ^{14}M_\odot$ for $R_{500} = 562_{-37}^{+50}$ kpc. This analysis establishes the existence of virialized, massive galaxy clusters at redshift $z\sim 1.6$, paving the way to the investigation of the progenitors of the most massive clusters today. Given its mass and the XDCP survey volume, XDCP J0044.0-2033 does not create significant tension with the WMAP-7 $\Lambda$CDM cosmology.
    Full-text · Article · Dec 2014 · The Astrophysical Journal
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Dusty, star-forming galaxies have a critical role in the formation and evolution of massive galaxies in the Universe. Using deep far-infrared imaging in the range 100-500um obtained with the Herschel telescope, we investigate the dust-obscured star formation in the galaxy cluster XDCP J0044.0-2033 at z=1.58, the most massive cluster at z >1.5, with a measured mass M200= 4.7x10$^{14}$ Msun. We perform an analysis of the spectral energy distributions (SEDs) of 12 cluster members (5 spectroscopically confirmed) detected with >3$\sigma$ significance in the PACS maps, all ULIRGs. The individual star formation rates (SFRs) lie in the range 155-824 Ms/yr, with dust temperatures of 24$\pm$35 K. We measure a strikingly high amount of star formation (SF) in the cluster core, SFR (< 250 kpc) > 1875$\pm$158 Ms/yr, 4x higher than the amount of star formation in the cluster outskirts. This scenario is unprecedented in a galaxy cluster, showing for the first time a reversal of the SF-density relation at z~1.6 in a massive cluster.
    Full-text · Article · Dec 2014 · Monthly Notices of the Royal Astronomical Society Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: With the goal of investigating the link between black hole (BH) and star formation (SF) activity, we study a deep sample of radio selected star forming galaxies (SFGs) and active galactic nuclei (AGNs). Using a multi-wavelength approach we characterize their host galaxies properties (stellar masses, optical colors, and morphology). Moreover, comparing the star formation rate derived from the radio and far-infrared luminosity, we found evidences that the main contribution to the radio emission in the radio-quiet AGNs is star-formation activity in their host galaxy.
    No preview · Article · Oct 2014 · Proceedings of the International Astronomical Union
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate various galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z=1.58, which constitutes the most extreme matter density peak at this redshift currently known. We analyze deep VLT/HAWK-I NIR data in the J- and Ks-bands, complemented by Subaru imaging in i and V, Spitzer observations at 4.5 micron, and new spectroscopic observations with VLT/FORS2. We detect a cluster-associated excess population of about 90 galaxies, which follows a centrally peaked, compact NFW galaxy surface density profile with a concentration of c200~10. Based on the Spitzer 4.5 micron imaging data, we measure a stellar mass fraction of fstar,500=(3.3+-1.4)% consistent with local values. The total J- and Ks-band galaxy luminosity functions of the core region yield characteristic magnitudes J* and Ks* consistent with expectations from simple z_f=3 burst models. However, a detailed look at the morphologies and color distributions of the spectroscopically confirmed members reveals that the most massive galaxies are undergoing a very active mass assembly epoch through merging processes. Consequently, the bright end of the cluster red-sequence is not in place, while at intermediate magnitudes [Ks*,Ks*+1.6] a red-locus population is present, which is then sharply truncated at magnitudes fainter than Ks*+1.6. The dominant cluster core population comprises post-quenched galaxies transitioning towards the red-sequence at intermediate magnitudes, while additionally a significant blue cloud population of faint star-forming galaxies is present even in the densest central regions. Our observations lend support to the scenario in which the dominant effect of the dense z~1.6 cluster environment is an accelerated mass assembly timescale through merging activity that is responsible for driving core galaxies across the mass quenching threshold of log(Mstar/Msun)~10.4.
    Full-text · Article · Jun 2014 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a detailed study of the iron content of the core of the high redshift cluster WARPJ1415.1+3612 (z=1.03). By comparing the central Fe mass excess observed in this system, M_Fe,exc = (1.67 +\- 0.40) x 10^9 M_sun, with those measured in local cool-core systems we infer that the bulk of the mass excess was already in place at z=1, when the age of the Universe was about half of what it is today. Our measures point to an early and intense period of star formation most likely associated with the formation of the BCG. Indeed, in the case of the power-law delay time distribution with slope -1, which best reproduces the data of WARPJ1415.1+3612, half of the supernovae explode within 0.4 Gyr, of the formation of the BCG. Finally, while for local cool-core clusters the Fe distribution is broader than the near infrared light distribution of the BCG, in WARPJ1415.1+3612 the two distributions are consistent indicating that the process responsible for broadening the Fe distribution in local systems has not yet started in this distant cluster.
    Full-text · Article · Jun 2014 · Astronomy and Astrophysics

Publication Stats

8k Citations
718.96 Total Impact Points

Institutions

  • 2015
    • Beijing Normal University
      • Department of Astronomy
      Peping, Beijing, China
    • University of Science and Technology of China
      • Department of Astronomy
      Luchow, Anhui Sheng, China
  • 2001-2014
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 2006-2012
    • INFN - Istituto Nazionale di Fisica Nucleare
      Frascati, Latium, Italy
  • 2010
    • Astronomical Observatory of Trieste
      Trst, Friuli Venezia Giulia, Italy
  • 2004-2010
    • National Institute of Astrophysics
      • Institute of Space Astrophysics and Cosmic Physics IASF - Rome
      Roma, Latium, Italy
    • Bowling Green State University
      • Department of Physics and Astronomy
      Боулинг-Грин, Ohio, United States
  • 2000-2010
    • European Southern Observatory
      Arching, Bavaria, Germany
  • 2008
    • Università degli Studi di Trieste
      • Department of Physics
      Trst, Friuli Venezia Giulia, Italy
  • 2007-2008
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
  • 1999-2008
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, MD, United States
  • 2002-2004
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
  • 1998
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
  • 1996-1998
    • University of Rome Tor Vergata
      • Dipartimento di Fisica
      Roma, Latium, Italy