The co-evolution of host galaxies and the active black holes which reside in their centre is one of the most important topics in modern observational cosmology. Here we present a study of the properties of obscured Active Galactic Nuclei (AGN) detected in the CDFS 1Ms observation and their host galaxies. We limited the analysis to the MUSIC area, for which deep K-band observations obtained with ISAAC@VLT are available, ensuring accurate identifications of the counterparts of the X-ray sources as well as reliable determination of photometric redshifts and galaxy parameters, such as stellar masses and star formation rates. In particular, we: 1) refined the X-ray/infrared/optical association of 179 sources in the MUSIC area detected in the Chandra observation; 2) studied the host galaxies observed and rest frame colors and properties. We found that X-ray selected (L_X>10^{42} erg s^{-1}) AGN show Spitzer colors consistent with both AGN and starburst dominated infrared continuum; the latter would not have been selected as AGN from infrared diagnostics. The host galaxies of X-ray selected obscured AGN are all massive (M_*>10^{10} M_sun) and, in 50% of the cases, are also actively forming stars (1/SSFR<t_{Hubble}) in dusty environments. The median L/LEdd value of the active nucleus is between 2% and 10% depending on the assumed M_{BH}/M_{*} ratio. Finally, we found that the X-ray selected AGN fraction increases with the stellar mass up to a value of ~30% at z>1 and M_*>3x10^{11} M_sun, a fraction significantly higher than in the local Universe for AGN of similar luminosities.
We analyze the link between active galactic nuclei (AGN) and mid-infrared flux using dust radiative transfer calculations of starbursts realized in hydrodynamical simulations. Focusing on the effects of galaxy dust, we evaluate diagnostics commonly used to disentangle AGN and star formation in ultraluminous infrared galaxies (ULIRGs). We examine these quantities as a function of time, viewing angle, dust model, AGN spectrum, and AGN strength in merger simulations representing two possible extremes of the ULIRG population: one is a typical gas-rich merger at z ~ 0, and the other is characterist…
In this paper, we characterize the infrared spectral energy distributions (SEDs) of mid-IR selected z~0.3-3.0 and L_IR~10^11-10^13Lsun galaxies, and study how their SEDs differ from those of local and high-z analogs. Our mid-IR flux-limited sample of 191 sources is unique in size, and spectral coverage, including Spitzer mid-IR spectroscopy. Here we add Herschel photometry at 250um, 350um, and 500um, which allows us to obtain accurate total IR luminosities, as well as constrain the relative contributions of AGN and starbursts to those luminosities. Our sample constitutes ~23% AGN (i.e. where t…
We present BayeSED, a general purpose tool for doing Bayesian analysis of SEDs by using whatever pre-existing model SED libraries or their linear combinations. The artificial neural networks (ANNs), principal component analysis (PCA) and multimodal nested sampling (MultiNest) techniques are employed to allow a highly efficient sampling of posterior distribution and the calculation of Bayesian evidence. As a demonstration, we apply this tool to a sample of hyperluminous infrared galaxies (HLIRGs). The Bayesian evidences obtained for a pure Starburst, a pure AGN, and a linear combination of Star…
Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts - that is, increased rates of star formation - in the most massive dark matter halos at early epochs. However, it remains unknown how soon after the Big Bang such massive starburst progenitors exist. The measured redshift distribution of dusty, massive starbursts has long been suspected to be biased low in redshift owing to selection effects, as confirmed by recent findings of systems out to redshift z~5. Here we repor…
We present Keck spectroscopic observations and redshifts for a sample of 767 Herschel-SPIRE selected galaxies (HSGs) at 250, 350, and 500um, taken with the Keck I Low Resolution Imaging Spectrometer (LRIS) and the Keck II DEep Imaging Multi-Object Spectrograph (DEIMOS). The redshift distribution of these SPIRE sources from the Herschel Multitiered Extragalactic Survey (HerMES) peaks at z=0.85, with 731 sources at z<2 and a tail of sources out to z~5. We measure more significant disagreement between photometric and spectroscopic redshifts (<delta_z>/(1+z)>=0.29) than is seen in non-infrared sel…
Using Spitzer-MIPS 24um imaging and Keck spectroscopy we examine the nature of the obscured star forming population in three clusters and three groups at z~0.9. These six systems are components of the Cl1604 supercluster, the largest structure imaged by Spitzer at redshifts near unity. We find that the average density of 24um-detected galaxies within the Cl1604 clusters is nearly twice that of the surrounding field and that this overdensity scales with the cluster's dynamical state. The 24um-bright members often appear optically unremarkable and exhibit only moderate [OII] line emission due to…
(abridged) We identify a numerically significant population of heavily obscured AGNs at z~0.5-1 in the Chandra Deep Field-South (CDF-S) and Extended Chandra Deep Field-South by selecting 242 X-ray undetected objects with infrared-based star formation rates (SFRs) substantially higher (a factor of 3.2 or more) than their SFRs determined from the UV after correcting for dust extinction. An X-ray stacking analysis of 23 candidates in the central CDF-S region using the 4 Ms Chandra data reveals a hard X-ray signal with an effective power-law photon index of Gamma=0.6_{-0.4}^{+0.3}, indicating a si…
A summary of mid-infrared continuum luminosities arising from dust is given for very luminous galaxies, Lir > 10^12 solar luminosities, with 0.005 < z < 3.2 containing active galactic nuclei (AGN), including 115 obscured AGN and 60 unobscured (type 1) AGN. All sources have been observed with the Spitzer Infrared Spectrograph. Obscured AGN are defined as having optical depth > 0.7 in the 9.7 um silicate absorption feature and unobscured AGN show silicate in emission. Luminosity vLv(8 um) is found to scale as (1+z)^2.6 to z = 2.8, and luminosities vLv(8 um) are approximately 3 times greater for …
Post-starbursts are galaxies in transition from the blue cloud to the red sequence. Although they are rare today, integrated over time they may be an important pathway to the red sequence. This work uses SDSS, GALEX, and WISE observations to identify the evolutionary sequence from starbursts to fully quenched post-starbursts in the narrow mass range $\log M(M_\odot) = 10.3-10.7$, and identifies "transiting" post-starbursts which are intermediate between these two populations. In this mass range, $\sim 0.3\%$ of galaxies are starbursts, $\sim 0.1\%$ are quenched post-starbursts, and $\sim 0.5\%…
We present optical to far-infrared photometry of 31 reddened QSOs that show evidence for radiatively driven outflows originating from AGN in their rest-frame UV spectra. We use these data to study the relationships between the AGN-driven outflows, and the AGN and starburst infrared luminosities. We find that FeLoBAL QSOs are invariably IR-luminous, with IR luminosities exceeding 10^{12} Solar luminosities in all cases. The AGN supplies 76% of the total IR emission, on average, but with a range from 20% to 100%. We find no evidence that the absolute luminosity of obscured star formation is affe…
We report the detection of extended X-ray emission around two powerful high-z radio galaxies (HzRGs) at z~3.6 (4C03.24 & 4C19.71) and use these to investigate the origin of extended, Inverse Compton (IC) powered X-ray halos at high z. The halos have X-ray luminosities of Lx~3e44 erg/s and sizes of ~60kpc. Their morphologies are broadly similar to the ~60-kpc long radio lobes around these galaxies suggesting they are formed from IC scattering by relativistic electrons in the radio lobes, of either CMB or FIR photons from the dust-obscured starbursts in these galaxies. These observations double …
We have used the European VLBI Network (EVN) to observe a sample of Lyman Break Analogs (LBAs), nearby (z < 0.3) galaxies with properties similar to the more distant Lyman Break Galaxies (LBGs). The study of LBGs may help define the feed-back relationship between black holes (BHs) and their host galaxies. Previous VLA observations have shown that the kpc-scale radio emission from LBAs is dominated by starbursts. The main targets of this VLBI experiment were selected because they possessed emission-line properties between starbursts and Type 2 (obscured) AGN. Eight targets (three star-forming L…
Our current understanding of the evolution of obscured accretion onto supermassive black holes is reviewed. We consider the literature results on the relation between the fraction of moderately obscured, Compton-thin AGN and redshift, and discuss the biases which possibly affect the various measurements. Then, we discuss a number of methods - from ultradeep X-ray observations to the detection of high-ionization optical emission lines - to select the population of the most heavily obscured, Compton-thick AGN, whose cosmological evolution is basically unknown. The space density of heavily obscur…
There are few observational constraints on how the escape of ionizing photons from starburst galaxies depends on galactic parameters. Here, we report on the first major detection of an ionization cone in NGC 5253, a nearby starburst galaxy. This high-excitation feature is identified by mapping the emission-line ratios in the galaxy using [S III] lambda 9069, [S II] lambda 6716, and H_alpha narrow-band images from the Maryland-Magellan Tunable Filter at Las Campanas Observatory. The ionization cone appears optically thin, which is suggestive of the escape of ionizing photons. The cone morpholog…
The nearly edge-on galaxy NGC4945 is one of the closest galaxies where an AGN and starburst coexist, and is one of the brightest sources at 100 keV. Near and mid-infrared spectroscopy have shown very strong obscuration of its central region, rivaled only in strength by some of the most deeply obscured ULIRGs. We aim to determine the spatial distribution of ISM features in the central 426x426 pc^2 of NGC4945. We map the central region of NGC4945 in three Spitzer-IRS modules (SH, SL and LL). We produce maps of the flux distribution of the starburst tracers [Ne II], [Ne III], [S III] and [S IV] a…
We summarize observations with the Spitzer Infrared Spectrograph (IRS) of 571 starbursts (strong PAH emission features), 128 obscured AGN (strong silicate absorption), and 39 unobscured AGN (silicate emission). Sources range in luminosity from 10^{8} to 10^{14} solar luminosities and continuously in redshift for 0 < z < 3. The most luminous starbursts and AGN evolve as (1+z)^{2.5} to z ~ 2.5; no clear evidence is found that this evolution ceases beyond z = 2.5. Dust obscuration in starbursts is determined by comparing PAH luminosity with ultraviolet luminosity and indicates severe obscuration …
NGC 7582 is defined as a Starburst/AGN galaxy, since its optical and X-Ray spectra reveal both characteristics. In this work, we show the results of a stellar population modeling in a datacube taken with the Gemini South telescope. We found that $\sim$ 90% of the light in the field of view is emitted by stars that are less than 1 billion years old. A strong burst occurred about $\sim$ 6 million years ago and has nearly solar metallicity. We also found a Wolf-Rayet cluster.
We report the discovery of a Compton-thick Active Galactic Nucleus (AGN) at z=4.76 in the 4 Ms Chandra Deep Field South. This object was selected as a V-band dropout in HST/ACS images and previously recognized as an AGN from optical spectroscopy. The 4 Ms Chandra observations show a significant (~4.2sigma) X-ray detection at the V-band dropout position. The X-ray source displays a hardness ratio of HR=0.23+-0.24, which, for a source at z~5, is highly suggestive of Compton-thick absorption. The source X-ray spectrum is seen above the background level in the energy range of ~0.9-4 keV, i.e., in …
We present results on low-resolution mid-infrared (MIR) spectra of 70 infrared-luminous galaxies obtained with the Infrared Spectrograph (IRS) onboard Spitzer. We selected sources from the European Large Area Infrared Survey (ELAIS) with S15 > 0.8 mJy and photometric or spectroscopic z > 1. About half of the sample are QSOs in the optical, while the remaining sources are galaxies, comprising both obscured AGN and starbursts. We classify the spectra using well-known infrared diagnostics, as well as a new one that we propose, into three types of source: those dominated by an unobscured AGN (QSOs…
We use SDSS spectra and optical to far-infrared photometry for a sample of 31 FeLoBAL QSOs to study the relationship between the AGN-driven outflows, and obscured star formation in their host galaxies. We find that FeLoBAL QSOs invariably have IR luminosities exceeding 10^12 Solar luminosities. The AGN supplies 75% of the total IR emission, on average, but with a range from 20% to 100%. We find a clear anticorrelation between the strength of the AGN-driven outflows and the contribution from star formation to the total IR luminosity, with a much higher chance of seeing a starburst contribution …
We present the results of HCN/HCO+/HNC J=4-3 transition line observations of the nearby starburst galaxy NGC 1614, obtained with ALMA Cycle 0. We find that high density molecular gas, traced with these lines, shows a velocity structure such that the northern (southern) side of the nucleus is redshifted (blueshifted) with respect to the nuclear velocity of this galaxy. The redshifted and blueshifted emission peaks are offset by ~0.6" at the northern and southern sides of the nucleus, respectively. At these offset positions, observations at infrared >3 micron indicate the presence of active dust…
We report ALMA Cycle 0 observations at 1.3mm of LESS J033229.4-275619 (XID403), an Ultraluminous Infrared Galaxy at $z=4.75$ in the Chandra Deep Field South hosting a Compton-thick QSO. The source is not resolved in our data at a resolution of $\sim$0.75 arcsec, placing an upper-limit of 2.5 kpc to the half-light radius of the continuum emission from heated-dust. After deconvolving for the beam size, however, we found a $\sim3σ$ indication of an intrinsic source size of $0.27\pm0.08$ arcsec (Gaussian FWHM), which would correspond to $r_{half}\sim0.9\pm0.3$ kpc. We build the far-IR SED of XID40…
We report the discovery of an active galactic nucleus (AGN) pair in the interacting galaxy system IRAS 20210+1121 at z = 0.056. An XMM-Newton observation reveals the presence of an obscured (Nh ~ 5 x 10^{23} cm^-2), Seyfert-like (L_{2-10 keV} = 4.7 x 10^{42} erg/s) nucleus in the northern galaxy, which lacks unambiguous optical AGN signatures. Our spectral analysis also provides strong evidence that the IR-luminous southern galaxy hosts a Type 2 quasar embedded in a bright starburst emission. In particular, the X-ray primary continuum from the nucleus appears totally depressed in the XMM-Newto…
We present a physical model for the origin of z~2 Dust-Obscured Galaxies (DOGs), a class of high-redshift ULIRGs selected at 24 micron which are particularly optically faint (24/R>1000). By combining N-body/SPH simulations of high redshift galaxy evolution with 3D polychromatic dust radiative transfer models, we find that luminous DOGs (with F24 > 0.3 mJy at z~2 are well-modeled as extreme gas-rich mergers in massive (~5x10^12-10^13 Msun) halos, with elevated star formation rates (~500-1000 Msun/yr) and/or significant AGN growth (Mdot > 0.5 Msun/yr), whereas less luminous DOGs are more diverse…
We present a thorough study of the specific star formation rates for MIPS 24um selected galaxies in the Coma cluster. We build galaxy spectral energy distributions using optical (u',g',r',i',z'), Near-infrared (J,H,Ks), and Mid to Far-infrared (IRAC and MIPS) photometry. New and archival spectra confirm 210 cluster members. Subsequently, the total infrared luminosity, galaxy stellar mass, and specific star formation rate for the members are determined by measuring best fit templates. Using an array of complementary diagnostics, we search for contaminating AGN, but find few. We compare obscured…
The role of galaxy mergers in fueling active galactic nuclei (AGN) is still debated, owing partly to selection effects inherent to studies of the merger/AGN connection. In particular, luminous AGN are often heavily obscured in late-stage mergers. Mid-infrared (IR) color selection of dust-enshrouded AGN with, e.g., the Wide-field Infrared Survey Explorer (WISE) has uncovered large new populations of obscured AGN. However, this method is sensitive mainly to AGN that dominate emission from the host. To understand how these selection biases affect mid-IR studies of the merger/AGN connection, we si…
We present spectroscopic results for all galaxies observed with the Spitzer Infrared Spectrograph (IRS) which also have total infrared fluxes f(ir) measured with the Infrared Astronomical Satellite (IRAS), also using AKARI photometry when available. Infrared luminosities and spectral energy distributions (SEDs) from 8 um to 160 um are compared to polycyclic aromatic hydrocarbon (PAH) emission from starburst galaxies or mid-infrared dust continuum from AGN at rest frame wavelengths ~ 8 um. A total of 301 spectra are analyzed for which IRS and IRAS include the same unresolved source, as measured…
Optically very faint R>25.5 sources detected by the Spitzer Space Telescope at 24um represent a very interesting population at redshift z [1.5-3]. They exhibit strong clustering properties, implying that they are hosted by very massive halos, and their mid-IR emission could be powered by either dust-enshrouded star-formation and/or by an obscured AGN. We report observations carried out with the MAMBO array at the IRAM 30m antenna on Pico Veleta of a candidate protocluster with five optically obscured sources selected from the 24um Spitzer sample of the First Look Survey. Interestingly, these s…
The aim of this study is to constrain the dynamics, structure and feeding of the compact nucleous of NGC4418, and to reveal the nature of the main hidden power source: starburst or AGN. We obtained high spatial resolution observations of NGC4418 at 1.4 and 5 GHz with MERLIN, and at 230 and 270 GHz with the SMA very extended configuration. We use the continuum morphology and flux density to estimate the size of the emitting region, the star formation rate and the dust temperature. Emission lines are used to study the kinematics through position-velocity diagrams. Molecular emission is studied w…
We present selected results on the X-ray spectroscopy of distant, obscured AGN as obtained with the ultra-deep (~3 Ms) XMM-Newton survey in the Chandra Deep Field South (CDF-S). One of the primary goals of the project is to characterize the X-ray spectral properties of heavily obscured and Compton-thick AGN over the range of redshifts and luminosities that are relevant in terms of their contribution to the X-ray background. The ultra-deep exposure, coupled with the XMM detector's spectral throughput, allowed us to accumulate X-ray spectra for more than 100 AGN to investigate the absorption dis…
We report the results of a deep SCUBA-2 850- and 450-$μ$m survey for dust-obscured ultra-luminous infrared galaxies (U/LIRGs) in the field of the z=1.46 cluster XCS J2215.9-1738. We detect a striking overdensity of sub-millimeter sources coincident with the core of this cluster: $\sim 3-4 \times$ higher than expected in a blank field. We use the likely radio and mid-infrared counterparts to show that the bulk of these sub-millimeter sources have spectroscopic or photometric redshifts which place them in the cluster and that their multi-wavelength properties are consistent with this association…
The European VLBI Network (EVN) has been used at two epochs in 2003 and 2009 to obtain multi-frequency high-resolution images of the merger galaxy NGC6240 in order to study the radio properties of all compact high-brightness components in the galaxy. Our observations at milli-arcsecond resolution detected the northern and southern nuclei and two radio components, which we interpret as long-lived luminous supernovae associated with the circum-nuclear starburst activity at the southern nucleus. The new VLBI data support the presence of an active galactic nucleus (AGN) together with starburst act…
We have used XMM-Newton to observe six Lyman Break Analogs (LBAs): members of the rare population of local galaxies that have properties that are very similar to distant Lyman Break Galaxies. Our six targets were specifically selected because they have optical emission-line properties that are intermediate between starbursts and Type 2 (obscured) AGN. Our new X-ray data provide an important diagnostic of the presence of an AGN. We find X-ray luminosities of order 10^{42} erg/s and ratios of X-ray to far-IR luminosities that are higher than values in pure starburst galaxies by factors ranging f…
Hot Dust-Obscured Galaxies (Hot DOGs) are a population of hyper-luminous infrared galaxies identified by the WISE mission from their very red mid-IR colors, and characterized by hot dust temperatures ($T>60~\rm K$). Several studies have shown clear evidence that the IR emission in these objects is powered by a highly dust-obscured AGN that shows close to Compton-thick absorption at X-ray wavelengths. Thanks to the high AGN obscuration, the host galaxy is easily observable, and has UV/optical colors usually consistent with those of a normal galaxy. Here we discuss a sub-population of 8 Hot DOGs…
Highly dust-obscured starbursting galaxies (submillimeter galaxies and their ilk) represent the most extreme sites of star-formation in the distant universe and contribute significantly to overall cosmic star-formation beyond z>1.5. Some stars formed in these environments may also explode as GRBs and contribute to the population of "dark" bursts. Here we present VLA wideband radio-continuum observations of 15 heavily dust-obscured Swift GRBs to search for radio synchrotron emission associated with intense star-formation in their host galaxies. Most of these targets (11) are not detected. Of th…
We present a general review of the current knowledge of IRAS 20551-4250 and its circumnuclear environment. This Ultraluminous Infrared Galaxy is one of the most puzzling sources of its class in the nearby Universe: the near-IR spectrum is typical of a galaxy experiencing a very intense starburst, but a highly obscured active nucleus is identified beyond 5 micron and possibly dominates the mid-IR energy output of the system. At longer wavelengths star formation is again the main driver of the global spectral shape and features. We interpret all the available IR diagnostics in the framework of s…
We use the 4Ms CDF-S survey to place direct X-ray constraints on the ubiquity of z~2 heavily obscured AGNs in K<22 BzK galaxies. Forty seven of the 222 BzK galaxies in the central region of the CDF-S are detected at X-ray energies, 11 of which have hard X-ray spectral slopes (Gamma<1) indicating the presence of heavily obscured AGN activity. The other 36 X-ray detected BzK galaxies appear to be relatively unobscured AGNs and starburst galaxies; we use X-ray variability analyses over a rest-frame baseline of ~3 years to further confirm the presence of AGN activity in many of these systems. The …
A multi-wavelength study of nearby starburst galaxy M 82
Maharashtra Udayagiri Mahavidyalaya（马哈拉施特拉乌达吉里学院）；North-West University（西北大学）；Swami Ramanand Teerth Marathawada University（斯瓦米·拉马南德·特思马拉塔瓦达大学）；Physical Research Laboratory（物理研究实验室）；National Institute for Theoretical and Computational Sciences (NITheCS)（国家理论计算科学研究所）
We discuss the possible origin of the double-peaked profiles recently observed in Lyman-Alpha Emitters (LAEs) at the epoch of reionization ($z \gtrsim 6.5$) from obscured active galactic nuclei (AGN). Combining the extent of the Lyman-$α$ near-zones estimated from the blue peak velocity offset in these galaxies, with the ionizing emissivity of quasars at $z \gtrsim 6$, we forecast the intrinsic UV and X-ray luminosities of the AGN needed to give rise to their double-peaked profiles. We also estimate the extent of the obscuration of the AGN by comparing their luminosities to those of similar qu…
We report on the detection of bright CO(4-3) line emission in two powerful, obscured quasars discovered in the SWIRE survey, SW022513 and SW022550 at z>3.4. We analyze the line strength and profile to determine the gas mass, dynamical mass and the gas dynamics for both galaxies. In SW022513 we may have found the first evidence for a molecular, AGN-driven wind in the early Universe. The line profile in SW022513 is broad (FWHM = 1000 km/s) and blueshifted by -200 km/s relative to systemic (where the systemic velocity is estimated from the narrow components of ionized gas lines, as is commonly do…
We present results from a spectral analysis of a sample of high-redshift (z>3) X-ray selected AGN in the 4 Ms Chandra Deep Field South (CDF-S), the deepest X-ray survey to date. The sample is selected using the most recent spectroscopic and photometric information available in this field. It consists of 34 sources with median redshift z=3.7, 80 median net counts in the 0.5-7 keV band and median rest-frame absorption-corrected luminosity $L_{2-10 \rmn{keV}}\approx1.5\times10^{44}\rmn{erg} \rmn{s^{-1}}$. Spectral analysis for the full sample is presented and the intrinsic column density distribu…
We present a {\it Chandra} observation of IRAS 19254--7245, a nearby ULIRG also known as {\it the Superantennae}. The high spatial resolution of {\it Chandra} allows us to disentangle for the first time the diffuse starburst emission from the embedded Compton-thick AGN. The 2-10 keV spectrum of the AGN emission is fitted by a flat power-law $Γ=1.3$) and a He-like Fe K$α$ line with EW$\sim$1.5 keV, consistent with previous observations. The Fe K$α$ line profile could be resolved as a blend of a neutral 6.4 keV line and an ionized 6.7 keV (He-like) or 6.9 keV (H-like) line. Variability is detect…
We have obtained spectroscopic confirmation with Hubble Space Telescope WFC3/G141 of a first sizeable sample of nine quiescent galaxies at 2.4<z<3.3. Their average near-UV/optical rest-frame spectrum is characterized by low attenuation (Av$\sim$0.6 mag) and a strong Balmer break, larger than the 4000 A break, corresponding to a fairly young age of $\sim$300 Myr. This formally classifies a substantial fraction of classically selected quiescent galaxies at z $\sim$ 3 as post-starbursts, marking their convergence to the quenching epoch. The rapid spectral evolution with respect to z $\sim$ 1.5 qu…
