arXiv subjects

M. Salvato

Publications and source records attributed to M. Salvato.

At least 127 records · Page 7Linked to original sources

arXiv2018

The environmental properties of radio-emitting AGN

We study the environmental properties of z<1.2 radio-selected AGN belonging to the ~2 square degrees of the COSMOS field, finding that about 20% of them appear within overdense structures. AGN with $P[1.4 GHz]>10^{23.5} W Hz^{-1} sr^{-1}$ are twice more likely to be found in clusters with respect to fainter sources (~38% vs ~15%), just as radio-selected AGN with stellar masses $M*>10^{11} M_\odot$ are twice more likely to be found in overdense environments with respect to objects of lower mass (~24% vs ~11%). Comparisons with galaxy samples further suggest that radio-selected AGN of large stellar mass tend to avoid underdense environments more than normal galaxies with the same stellar content. Stellar masses also seem to determine the location of radio-active AGN within clusters: ~100% of the sources found as satellite galaxies have $M*<10^{11.3} M_\odot$, while ~100% of the AGN coinciding with a cluster central galaxy have $M*>10^{11} M_\odot$. No different location within the cluster is instead observed for AGN of various radio luminosities. Radio AGN which also emit in the MIR show a marked preference to be found as isolated galaxies (~70%) at variance with those also active in the X-ray which all seem to reside within overdensities. What emerges from our work is a scenario whereby physical processes on sub-pc and kpc scales (e.g. emission respectively related to the AGN and to star formation) are strongly interconnected with the large-scale environment of the AGN itself.

astro-ph.GA↗

arXiv2018

The VANDELS ESO public spectroscopic survey

VANDELS is a uniquely-deep spectroscopic survey of high-redshift galaxies with the VIMOS spectrograph on ESO's Very Large Telescope (VLT). The survey has obtained ultra-deep optical (0.48 < lambda < 1.0 micron) spectroscopy of ~2100 galaxies within the redshift interval 1.0 < z < 7.0, over a total area of ~0.2 sq. degrees centred on the CANDELS UDS and CDFS fields. Based on accurate photometric redshift pre-selection, 85% of the galaxies targeted by VANDELS were selected to be at z>=3. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the fundamental aim of the survey is to provide the high signal-to-noise ratio spectra necessary to measure key physical properties such as stellar population ages, masses, metallicities and outflow velocities from detailed absorption-line studies. Using integration times calculated to produce an approximately constant signal-to-noise ratio (20 < t_int < 80 hours), the VANDELS survey targeted: a) bright star-forming galaxies at 2.4 < z < 5.5, b) massive quiescent galaxies at 1.0 < z < 2.5, c) fainter star-forming galaxies at 3.0 < z < 7.0 and d) X-ray/Spitzer-selected active galactic nuclei and Herschel-detected galaxies. By targeting two extragalactic survey fields with superb multi-wavelength imaging data, VANDELS will produce a unique legacy data set for exploring the physics underpinning high-redshift galaxy evolution. In this paper we provide an overview of the VANDELS survey designed to support the science exploitation of the first ESO public data release, focusing on the scientific motivation, survey design and target selection.

astro-ph.GA↗

arXiv2018

The DEIMOS 10k spectroscopic survey catalog of the COSMOS field

We present a catalog of 10718 objects in the COSMOS field observed through multi-slit spectroscopy with the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II telescope in the wavelength range ~5500-9800A. The catalog contains 6617 objects with high-quality spectra (two or more spectral features), and 1798 objects with a single spectroscopic feature confirmed by the photometric redshift. For 2024 typically faint objects we could not obtain reliable redshifts. The objects have been selected from a variety of input catalogs based on multi-wavelength observations in the field, and thus have a diverse selection function, which enables the study of the diversity in the galaxy population. The magnitude distribution of our objects is peaked at I_AB~23 and K_AB~21, with a secondary peak at K_AB~24. We sample a broad redshift distribution in the range 0 0.65 with chance probabilities <4xE-4$, some of which are clearly related to protocluster structures of sizes >10 Mpc. An object-to-object comparison with a multitude of other spectroscopic samples in the same field shows that our DEIMOS sample is among the best in terms of fraction of spectroscopic failures and relative redshift accuracy. We have determined the fraction of spectroscopic blends to about 0.8% in our sample. This is likely a lower limit and at any rate well below the most pessimistic expectations. Interestingly, we find evidence for strong lensing of Ly-alpha background emitters within the slits of 12 of our target galaxies, increasing their apparent density by about a factor of 4.

astro-ph.GA↗

arXiv2018

The VANDELS ESO public spectroscopic survey: observations and first data release

This paper describes the observations and the first data release (DR1) of the ESO public spectroscopic survey "VANDELS, a deep VIMOS survey of the CANDELS CDFS and UDS fields". VANDELS' main targets are star-forming galaxies at 2.4<z<5.5 and massive passive galaxies at 1<z<2.5. By adopting a strategy of ultra-long exposure times, from 20 to 80 hours per source, VANDELS is designed to be the deepest ever spectroscopic survey of the high-redshift Universe. Exploiting the red sensitivity of the VIMOS spectrograph, the survey has obtained ultra-deep spectra covering the wavelength 4800-10000 A with sufficient signal-to-noise to investigate the astrophysics of high-redshift galaxy evolution via detailed absorption line studies. The VANDELS-DR1 is the release of all spectra obtained during the first season of observations and includes data for galaxies for which the total (or half of the total) scheduled integration time was completed. The release contains 879 individual objects with a measured redshift and includes fully wavelength and flux-calibrated 1D spectra, the associated error spectra, sky spectra and wavelength-calibrated 2D spectra. We also provide a catalog with the essential galaxy parameters, including spectroscopic redshifts and redshift quality flags. In this paper we present the survey layout and observations, the data reduction and redshift measurement procedure and the general properties of the VANDELS-DR1 sample. We also discuss the spectroscopic redshift distribution, the accuracy of the photometric redshifts and we provide some examples of data products. All VANDELS-DR1 data are publicly available and can be retrieved from the ESO archive. Two further data releases are foreseen in the next 2 years with a final release scheduled for June 2020 which will include improved re-reduction of the entire spectroscopic data set. (abridged)

astro-ph.GA↗

arXiv2017

Evidence for Merger-Driven Growth in Luminous, High-z, Obscured AGN in the CANDELS/COSMOS Field

While major mergers have long been proposed as a driver of both AGN activity and the M-sigma relation, studies of moderate to high redshift Seyfert-luminosity AGN hosts have found little evidence for enhanced rates of interactions. However, both theory and observation suggest that while these AGN may be fueled by stochastic accretion and secular processes, high-luminosity, high-redshift, and heavily obscured AGN are the AGN most likely to be merger-driven. To better sample this population of AGN, we turn to infrared selection in the CANDELS/COSMOS field. Compared to their lower-luminosity and less obscured X-ray-only counterparts, IR-only AGN (luminous, heavily obscured AGN) are more likely to be classified as either irregular (50$^{+12}_{-12}$% vs. 9$^{+5}_{-2}$%) or asymmetric (69$^{+9}_{-13}$% vs. 17$^{+6}_{-4}$%) and are less likely to have a spheroidal component (31$^{+13}_{-9}$% vs. 77$^{+4}_{-6}$%). Furthermore, IR-only AGN are also significantly more likely than X-ray-only AGN (75$^{+8}_{-13}$% vs. 31$^{+6}_{-6}$%) to be classified either as interacting or merging in a way that significantly disturbs the host galaxy or disturbed though not clearly interacting or merging, which potentially represents the late stages of a major merger. This suggests that while major mergers may not contribute significantly to the fueling of Seyfert luminosity AGN, interactions appear to play a more dominant role in the triggering and fueling of high-luminosity heavily obscured AGN.

astro-ph.GA↗

arXiv2017

Calibrating chemical multisensory devices for real world applications: An in-depth comparison of quantitative Machine Learning approaches

Chemical multisensor devices need calibration algorithms to estimate gas concentrations. Their possible adoption as indicative air quality measurements devices poses new challenges due to the need to operate in continuous monitoring modes in uncontrolled environments. Several issues, including slow dynamics, continue to affect their real world performances. At the same time, the need for estimating pollutant concentrations on board the devices, espe- cially for wearables and IoT deployments, is becoming highly desirable. In this framework, several calibration approaches have been proposed and tested on a variety of proprietary devices and datasets; still, no thorough comparison is available to researchers. This work attempts a benchmarking of the most promising calibration algorithms according to recent literature with a focus on machine learning approaches. We test the techniques against absolute and dynamic performances, generalization capabilities and computational/storage needs using three different datasets sharing continuous monitoring operation methodology. Our results can guide researchers and engineers in the choice of optimal strategy. They show that non-linear multivariate techniques yield reproducible results, outperforming lin- ear approaches. Specifically, the Support Vector Regression method consistently shows good performances in all the considered scenarios. We highlight the enhanced suitability of shallow neural networks in a trade-off between performance and computational/storage needs. We confirm, on a much wider basis, the advantages of dynamic approaches with respect to static ones that only rely on instantaneous sensor array response. The latter have been shown to be best choice whenever prompt and precise response is needed.

cs.AI↗

arXiv2017

Active Galactic Nuclei: what's in a name?

Active Galactic Nuclei (AGN) are energetic astrophysical sources powered by accretion onto supermassive black holes in galaxies, and present unique observational signatures that cover the full electromagnetic spectrum over more than twenty orders of magnitude in frequency. The rich phenomenology of AGN has resulted in a large number of different "flavours" in the literature that now comprise a complex and confusing AGN "zoo". It is increasingly clear that these classifications are only partially related to intrinsic differences between AGN, and primarily reflect variations in a relatively small number of astrophysical parameters as well the method by which each class of AGN is selected. Taken together, observations in different electromagnetic bands as well as variations over time provide complementary windows on the physics of different sub-structures in the AGN. In this review, we present an overview of AGN multi-wavelength properties with the aim of painting their "big picture" through observations in each electromagnetic band from radio to gamma-rays as well as AGN variability. We address what we can learn from each observational method, the impact of selection effects, the physics behind the emission at each wavelength, and the potential for future studies. To conclude we use these observations to piece together the basic architecture of AGN, discuss our current understanding of unification models, and highlight some open questions that present opportunities for future observational and theoretical progress.

astro-ph.GA↗

arXiv2017

Inferring Compton-thick AGN candidates at z>2 with Chandra using the >8 keV restframe spectral curvature

To fully understand cosmic black hole growth we need to constrain the population of heavily obscured active galactic nuclei (AGN) at the peak of cosmic black hole growth ($z\sim$1-3). Sources with obscuring column densities higher than $\mathrm{10^{24}}$ atoms $\mathrm{cm^{-2}}$, called Compton-thick (CT) AGN, can be identified by excess X-ray emission at $\sim$20-30 keV, called the "Compton hump". We apply the recently developed Spectral Curvature (SC) method to high-redshift AGN (2 5\times 10^{43}}$ erg $\mathrm{s^{-1}}$. In the Cosmological evolution survey (COSMOS), we find an observed CT fraction of $\mathrm{15^{+4}_{-3}\%}$ (40/272) or $\mathrm{32\pm11 \%}$ when corrected for the survey sensitivity. When comparing to low redshift AGN with similar X-ray luminosities, our results imply the CT AGN fraction is consistent with having no redshift evolution. Finally, we provide SC equations that can be used to find high-redshift CT AGN (z>1) for current (XMM-Newton) and future (eROSITA and ATHENA) X-ray missions.

astro-ph.HE↗

arXiv2017

The COSMOS2015 galaxy stellar mass function: 13 billion years of stellar mass assembly in 10 snapshots

We measure the stellar mass function (SMF) of galaxies in the COSMOS field up to $z\sim6$. We select them in the near-IR bands of the COSMOS2015 catalogue, which includes ultra-deep photometry from UltraVISTA-DR2, SPLASH, and Subaru/Hyper-SuprimeCam. At $z>2.5$ we use new precise photometric redshifts with error $σ_z=0.03(1+z)$ and an outlier fraction of $12\%$, estimated by means of the unique spectroscopic sample of COSMOS. The increased exposure time in the DR2, along with our panchromatic detection strategy, allow us to improve the stellar mass completeness at high $z$ with respect to previous UltraVISTA catalogues. We also identify passive galaxies through a robust colour-colour selection, extending their SMF estimate up to $z=4$. Our work provides a comprehensive view of galaxy stellar mass assembly between $z=0.1$ and 6, for the first time using consistent estimates across the entire redshift range. We fit these measurements with a Schechter function, correcting for Eddington bias. We compare the SMF fit with the halo mass function predicted from $Λ$CDM simulations. We find that at $z>3$ both functions decline with a similar slope in the high-mass end. This feature could be explained assuming that the mechanisms that quench star formation in massive haloes become less effective at high redshift; however further work needs to be done to confirm this scenario. Concerning the SMF low-mass end, it shows a progressive steepening as moving towards higher redshifts, with $α$ decreasing from $-1.47_{-0.02}^{+0.02}$ at $z\simeq0.1$ to $-2.11_{-0.13}^{+0.30}$ at $z\simeq5$. This slope depends on the characterisation of the observational uncertainties, which is crucial to properly remove the Eddington bias. We show that there is currently no consensus on the method to quantify such errors: different error models result in different best-fit Schechter parameters. [Abridged]

astro-ph.GA↗

arXiv2017

ESO-Athena Synergy White Paper

The Advanced Telescope for High ENergy Astrophysics (Athena) is the X-ray observatory mission selected by ESA within its Cosmic Vision 2015-2025 programme to address the Hot and Energetic Universe scientific theme. The ESO-Athena Synergy Team (EAST) has been tasked to single out the potential scientific synergies between Athena and optical/near-infrared (NIR) and sub/mm ground based facilities, in particular those of ESO (i.e., the VLT and ELT, ALMA and APEX), by producing a White Paper to identify and develop the: 1. needs to access ESO ground-based facilities to achieve the formulated Athena science objectives; 2. needs to access Athena to achieve the formulated science objectives of ESO facilities contemporary to Athena; 3. science areas where the synergetic use of Athena and ESO facilities in the late 2020s will result in scientific added value. Community input to the process happened primarily via a dedicated ESO - Athena Synergy Workshop that took place on Sept. 14 - 16, 2016 at ESO, Garching. This White Paper presents the results of the EAST's work, sorted by synergy area, and deals with the following topics: 1. the Hot Universe: Early groups and clusters and their evolution, Physics of the Intracluster medium, Missing baryons in cosmic filaments; 2. the Energetic Universe: Supermassive black hole (SMBH) history, SMBH accretion disks, Active Galactic Nuclei feedback - Molecular outflows, Ultra-fast outflows, Accretion Physics, Transient Science; 3. Observatory Science: Star Formation, Stars. It then discusses the optical-NIR-sub-mm perspective by providing details on VLT/MOONS, the E-ELT instruments, in particular the MOS, VISTA/4MOST, the ESO and ALMA archives, future ALMA and ESO developments, and finally the (likely) ESO - Athena astronomical scene in the 2020s. (abridged)

astro-ph.HE↗

arXiv2017

VLA-COSMOS 3GHz Large Project: The infrared-radio correlation of star-forming galaxies and AGN to $z\lesssim6$

We examine the behaviour of the infrared-radio correlation (IRRC) over the range $0<z<6$ using new, highly sensitive 3GHz observations with the Karl G. Jansky Very Large Array (VLA) and infrared data from the Herschel Space Observatory in the 2deg$^{2}$ COSMOS field. We distinguish between objects where emission is believed to arise solely from star-formation, and those where an active galactic nucleus (AGN) is thought to be present. We account for non-detections in the radio or in the infrared using a doubly-censored survival analysis. We find that the IRRC of star-forming galaxies, quantified by the infrared-to-1.4GHz radio luminosity ratio ($q_{\rm TIR}$), decreases with increasing redshift: $q_{\rm TIR}(z)=(2.88\pm0.03)(1+z)^{-0.19\pm0.01}$. Moderate-to-high radiative luminosity AGN do not follow the same $q_{\rm TIR}$$(z)$ trend, having a lower normalisation and steeper decrease with redshift. We cannot rule out the possibility that unidentified AGN contributions only to the radio regime may be steepening the observed $q_{\rm TIR}(z)$ trend of the star-forming population. An increasing fractional contribution to the observed 3GHz flux by free-free emission of star-forming galaxies may also affect the derived evolution. However, we find that the standard (M82-based) assumption of the typical radio spectral energy distribution (SED) for star-forming galaxies is inconsistent with our results. This suggests a more complex shape of the typical radio SED for star-forming galaxies, and that imperfect $K$ corrections in the radio may govern the derived redshift trend of $q_{\rm TIR}$. Lastly, we present a redshift-dependent relation between rest-frame 1.4GHz radio luminosity and star formation rate taking the derived redshift trend into account.

astro-ph.GA↗

arXiv2017

Observational constraints on the specific accretion-rate distribution of X-ray selected AGN

This paper estimates the specific accretion-rate distribution of AGN using a sample of 4821 X-ray sources from both deep and shallow surveys. The specific accretion-rate distribution is defined as the probability of a galaxy with a given stellar mass and redshift hosting an active nucleus with a certain specific accretion rate. We find that the probability of a galaxy hosting an AGN increases with decreasing specific accretion rate. There is evidence that this trend reverses at low specific accretion rates, $λ<10^{-4}-10^{-3}$ (in Eddington units). There is also a break close to the Eddington limit, above which the probability of an accretion event decreases steeply. The specific accretion-rate distribution evolves such that the fraction of AGN among galaxies drops toward lower redshifts. This decrease in the AGN duty cycle is responsible for the strong evolution of the accretion density of the Universe from redshift $z\approx1-1.5$ to the present day. Our analysis also suggests that this evolution is accompanied by a decoupling of accretion events onto black holes from the formation of stars in galaxies. There is also evidence that at earlier times the relative probability of high vs low specific accretion-rate events among galaxies increases. We argue that this differential redshift evolution of the AGN duty cycle with respect to $λ$ produces the AGN downsizing trend, whereby luminous sources peak at earlier epochs compared to less luminous ones. Finally, we also find a stellar-mass dependence of the specific accretion-rate distribution, with more massive galaxies avoiding high specific accretion-rate events.

astro-ph.HE↗

arXiv2017

X-ray constraints on the fraction of obscured AGN at high accretion luminosities

The wide-area XMM-XXL X-ray survey is used to explore the fraction of obscured AGN at high accretion luminosities, $L_X (\rm 2-10 \, keV) > 10^{44} \, erg \,s ^{-1}$, and out to redshift $z\approx1.5$. The sample covers an area of about $\rm14\,deg^2$ and provides constraints on the space density of powerful AGN over a wide range of neutral hydrogen column densities extending beyond the Compton-thick limit, $\rm N_H\approx10^{24}\,cm^{-2}$. The fraction of obscured Compton-thin ($\rm N_H=10^{22}-10^{24}\,cm^{-2}$) AGN is estimated to be $\approx0.35$ for luminosities $L_X(\rm 2-10\,keV)>10^{44}\,erg\,s^{-1}$ independent of redshift. For less luminous sources the fraction of obscured Compton-thin AGN increases from $0.45\pm0.10$ at $z=0.25$ to $0.75\pm0.05$ at $z=1.25$. Studies that select AGN in the infrared via template fits to the observed Spectral Energy Distribution of extragalactic sources estimate space densities at high accretion luminosities consistent with the XMM-XXL constraints. There is no evidence for a large population of AGN (e.g. heavily obscured) identified in the infrared and missed at X-ray wavelengths. We further explore the mid-infrared colours of XMM-XXL AGN as a function of accretion luminosity, column density and redshift. The fraction of XMM-XXL sources that lie within the mid-infrared colour wedges defined in the literature to select AGN is primarily a function of redshift. This fraction increases from about 20-30% at z=0.25 to about 50-70% at $z=1.5$.

astro-ph.HE↗

arXiv2017

The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population

(abridged) We study the composition of the faint radio population selected from the VLA-COSMOS 3GHz Large Project. The survey covers a 2.6sq.deg. area with a mean rms of ~2.3uJy/b, cataloging 10830 sources (>5sigma). Combining these radio data with optical, near-infrared (UltraVISTA), mid-infrared (Spitzer/IRAC) data, and X-ray data (Chandra), we find counterparts to radio sources for ~93% of the radio sample (in the areas of the COSMOS field not affected by saturated or bright sources in the optical to NIR bands), reaching out to z<6. We further classify the sources as star forming galaxies or AGN based on various criteria, such as X-ray luminosity, observed MIR color, UV-FIR spectral-energy distribution, rest-frame NUV-optical color corrected for dust extinction, and radio-excess relative to that expected from the hosts' star-formation rate. We separate the AGN into sub-samples dominated by low-to-moderate and moderate-to-high radiative luminosity AGN, candidates for high-redshift analogues to local low- and high-excitation emission line AGN, respectively. We study the fractional contributions of these sub-populations down to radio flux levels of ~11uJy at 3GHz (or ~20uJy at 1.4GHz assuming a spectral index of -0.7). We find that the dominant fraction at 1.4GHz flux densities above ~200uJy is constituted of low-to-moderate radiative luminosity AGN. Below densities of ~100uJy the fraction of star-forming galaxies increases to ~60%, followed by the moderate-to-high radiative luminosity AGN (~20%), and low-to-moderate radiative luminosity AGN (~20%). Based on this observational evidence, we extrapolate the fractions down to sensitivities of the SKA. Our estimates suggest that at the faint flux limits to be reached by the SKA1 surveys, a selection based only on radio flux limits can provide a simple tool to efficiently identify samples highly (>75%) dominated by star-forming galaxies.

astro-ph.GA↗

arXiv2017

SPIDERS: Selection of spectroscopic targets using AGN candidates detected in all-sky X-ray surveys

SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV survey running in parallel to the eBOSS cosmology project. SPIDERS will obtain optical spectroscopy for large numbers of X-ray-selected AGN and galaxy cluster members detected in wide area eROSITA, XMM-Newton and ROSAT surveys. We describe the methods used to choose spectroscopic targets for two sub-programmes of SPIDERS: X-ray selected AGN candidates detected in the ROSAT All Sky and the XMM-Newton Slew surveys. We have exploited a Bayesian cross-matching algorithm, guided by priors based on mid-IR colour-magnitude information from the WISE survey, to select the most probable optical counterpart to each X-ray detection. We empirically demonstrate the high fidelity of our counterpart selection method using a reference sample of bright well-localised X-ray sources collated from XMM-Newton, Chandra and Swift-XRT serendipitous catalogues, and also by examining blank-sky locations. We describe the down-selection steps which resulted in the final set of SPIDERS-AGN targets put forward for spectroscopy within the eBOSS/TDSS/SPIDERS survey, and present catalogues of these targets. We also present catalogues of ~12000 ROSAT and ~1500 XMM-Newton Slew survey sources which have existing optical spectroscopy from SDSS-DR12, including the results of our visual inspections. On completion of the SPIDERS program, we expect to have collected homogeneous spectroscopic redshift information over a footprint of ~7500 deg$^2$ for >85 percent of the ROSAT and XMM-Newton Slew survey sources having optical counterparts in the magnitude range 17<r<22.5, producing a large and highly complete sample of bright X-ray-selected AGN suitable for statistical studies of AGN evolution and clustering.

astro-ph.GA↗

arXiv2017

The VLA-COSMOS 3~GHz Large Project: AGN and host-galaxy properties out to z$\lesssim$6

We explore the multiwavelength properties of AGN host galaxies for different classes of radio-selected AGN out to z$\lesssim$6 via a multiwavelength analysis of about 7700 radio sources in the COSMOS field. The sources were selected with the Very Large Array (VLA) at 3 GHz (10 cm) within the VLA-COSMOS 3 GHz Large Project, and cross-matched with multiwavelength ancillary data. This is the largest sample of high-redshift (z$\lesssim$6) radio sources with exquisite photometric coverage and redshift measurements available. We constructed a sample of moderate-to-high radiative luminosity AGN (HLAGN) via spectral energy distribution (SED) decomposition combined with standard X-ray and mid-infrared diagnostics. Within the remainder of the sample we further identified low-to-moderate radiative luminosity AGN (MLAGN) via excess in radio emission relative to the star formation rates in their host galaxies. We show that AGN power in HLAGN occurs predominantly in radiative form, while MLAGN display a substantial mechanical AGN luminosity component. We found significant differences in the host properties of the two AGN classes, as a function of redshift. At z$<$1.5, MLAGN appear to reside in significantly more massive and less star-forming galaxies compared to HLAGN. At z$>$1.5, we observed a reversal in the behaviour of the stellar mass distributions with the HLAGN populating the higher stellar mass tail. We interpret this finding as a possible hint of the downsizing of galaxies hosting HLAGN, with the most massive galaxies triggering AGN activity earlier than less massive galaxies, and then fading to MLAGN at lower redshifts. Our conclusion is that HLAGN and MLAGN samples trace two distinct galaxy and AGN populations in a wide range of redshifts, possibly resembling the radio AGN types often referred to as radiative- and jet-mode (or high- and low-excitation), respectively.

astro-ph.GA↗

arXiv2017

The VLA-COSMOS 3 GHz Large Project: The cosmic star formation history since z~5

We make use of the deep Karl G. Jansky Very Large Array (VLA) COSMOS radio observations at 3 GHz to infer radio luminosity functions of star-forming galaxies up to redshifts of z~5 based on approximately 6000 detections with reliable optical counterparts. This is currently the largest radio-selected sample available out to z~5 across an area of 2 square degrees with a sensitivity of rms=2.3 ujy/beam. By fixing the faint and bright end shape of the radio luminosity function to the local values, we find a strong redshift trend that can be fitted with a pure luminosity evolution L~(1+z)^{(3.16 +- 0.2)-(0.32 +- 0.07) z}. We estimate star formation rates (SFRs) from our radio luminosities using an infrared (IR)-radio correlation that is redshift dependent. By integrating the parametric fits of the evolved luminosity function we calculate the cosmic SFR density (SFRD) history since z~5. Our data suggest that the SFRD history peaks between 2 1000 Msol/yr) contribute an additional <2% in the entire observed redshift range. We find evidence of a potential underestimation of SFRD based on ultraviolet (UV) rest-frame observations of Lyman break galaxies (LBGs) at high redshifts (z>4) on the order of 15-20%, owing to appreciable star formation in highly dust-obscured galaxies, which might remain undetected in such UV observations.

astro-ph.GA↗

arXiv2017

AGN vs. host galaxy properties in the COSMOS field

The coeval AGN and galaxy evolution and the observed local relations between SMBHs and galaxy properties suggest some connection or feedback between SMBH growth and galaxy build-up. We looked for correlations between properties of X-ray detected AGN and their FIR detected host galaxies, to find quantitative evidences for this connection, highly debated in the latest years. We exploit the rich multi-wavelength data set available in the COSMOS field for a large sample (692 sources) of AGN and their hosts, in the redshift range $0.1<z<4$. We use X-ray data to select AGN and determine their properties (intrinsic luminosity and nuclear obscuration), and broad-band SED fitting to derive host galaxy properties (stellar mass $M_*$ and star formation rate SFR). We find that the AGN 2-10 keV luminosity ($L_{\rm X}$) and the host $8-1000~μm$ star formation luminosity ($L_{\rm IR}^{\rm SF}$) are significantly correlated. However, the average host $L_{\rm IR}^{\rm SF}$ has a flat distribution in bins of AGN $L_{\rm X}$, while the average AGN $L_{\rm X}$ increases in bins of host $L_{\rm IR}^{\rm SF}$, with logarithmic slope of $\sim0.7$, in the redshifts range $0.4<z<1.2$. We also discuss the comparison between the distribution of these two quantities and the predictions from hydro-dynamical simulations. Finally we find that the average column density ($N_H$) shows a positive correlation with the host $M_*$, at all redshifts, but not with the SFR (or $L_{\rm IR}^{\rm SF}$). This translates into a negative correlation with specific SFR. Our results are in agreement with the idea that BH accretion and SF rates are correlated, but occur with different variability time scales. The presence of a positive correlation between $N_H$ and host $M_*$ suggests that the X-ray $N_H$ is not entirely due to the circum-nuclear obscuring torus, but may also include a contribution from the host galaxy.

astro-ph.GA↗