I will present the first results from a mid-infrared survey of local AGN using the CanariCam instrument on the 10.4m Gran Telescopio Canarias (GTC). We are obtaining diffraction limited (angular resolution 0.3-0.5") imaging and spectroscopic mid-IR observations as part of an ESO/GTC large programme and CanariCam guaranteed time for a total of ~280 hours. The sample is composed of approximately 100 local AGN covering nearly six orders of magnitude in AGN luminosity and including different types of AGN: LINERs, Seyfert 1s, Seyfert 2s, QSO, radio galaxies, and (U)LIRGs. The main goals of this project are:
(1) to test if the dusty tori of the AGN Unified Model is valid for all types of AGN,
(2) to study the nuclear star formation activity and obscuration of local AGN, and
(3) to explore the role of the dusty torus in low luminosity AGN.
Cosmological simulations predict that matter in the Universe is distributed in a network of intersecting filaments known as the "cosmic web". These streams are thought to feed galaxies located at the dense nodes of this web and ultimately super-massive black holes at their center that may occasionally power quasars. To date, emission from these filaments has not been detected, consistent with current predictions for their surface brightness. As such, we are conducting a narrow-band imaging survey of the field around bright quasars, targeting the Lyman alpha line. The idea is that the radiation from a quasar can, like a flashlight, illuminate the cosmic web and, after being reprocessed by the gas (e.g. recombination, scattering), teach us about the physical properties of the medium. I will present the first results from our survey: in particular, the striking observations of two z=2 quasars which show unprecedentedly large extended structure never seen before (about 500 physical kpc), up to the scale of the cosmic web. The data were obtained with the LRIS instrument on Keck I, using custome-built narrow-band filters that match the Lyman alpha line at the redshift of the targets.
The empirical relations in the black hole-accretion disk-relativistic jet system and physical processes behind these relations are still poorly understood in AGN, partly because they operate close to the black hole within the central light year. Very long baseline array (VLBA) provides unparalleled resolution at 15 GHz with which to observe the jet components at sub-milliarcsecond scales, corresponding to sub-pc-scales for local blazars. We combine the radio VLBA observations/monitoring of jets and optical spectroscopic, X-ray, and gamma-ray observations of their host galaxies to explore the link between the jet kinematics, jet radio emission, optical continuum and emission line flares of radio-loud AGN (blazars), and radiation mechanisms operating in the innermost parsec-scale region of blazars. I will present the evidence for correlated variability of emission from jet componets, non-thermal optical flares being generated in the innermost part of the jet, existence of outflowing (non-virial) broad-line region in blazar, and the jet model which may account for the most of multi-band data.
Low-luminosity radio galaxies, most of them showing a Fanaroff-Riley I (FR~I) radio morphology, are interesting objects and common in the local universe: they are associated with giant elliptical galaxies hosting the most massive black holes and often they lie at the center of clusters of galaxies. However, the steepness of the luminosity function of radio galaxies and the tight relation between redshift and luminosity make the flux-limited samples of distant radio-loud AGN more abundant in powerful radio galaxies, rather than low-power counterpart. Therefore, Chiaberge et al. (2009) selected the first sizeable sample of FRI candidates at 1<z<3, in the COSMOS field. I studied the Spectral Energy Distributions of this sample of low-power radio galaxies from the far-UV to the Mid-IR wavelenghts. Our results show that the hosts of these high-z low-luminosity radio sources are old massive galaxies, similar to the local FR Is. However, the UV and MIR excesses indicate the possible significant contribution from star formation and/or nuclear activity in such bands, not seen in low-z FR Is.
High-redshift quasars provide us with unique information about the evolution of supermassive black holes (SMBHs) and the intergalactic medium (IGM) at early cosmic time. Over the last decade, numerous studies have established a sample of ~ 60 quasars at 5.5 < z < 6.5, mostly discovered in optical surveys (i.e. SDSS and CFHTLS). Among the key results from these studies are the existence of SMBHs less than a Gyr after the Big Bang, and the presence of almost complete Gunn-Peterson absorption, indicating a rapid increase in the IGM neutral fraction and the end of the reionization at z ~ 6. These key findings strongly suggest that fundamental changes are happening in the IGM at z ~ 6-7. The discovery and characterization of a statistically significant sample of bright quasars in this redshift range is crucial to further study this important era in the history of the Universe. The Panoramic Survey Telescope & Rapid Response System 1 (Pan-STARRS1, PS1) is successfully surveying 3/4 of the sky in the filters g, r, i, z and y. PS1 represents a fundamental step forward in high-redshift quasar searches for three reasons: 1) it covers two times the area observed with SDSS; 2) it goes significantly deeper (0.5 - 1 mag) than SDSS in the reddest bands where z ~ 6 quasars are visible; and 3) the y-band enables the search for luminous quasars beyond the SDSS limit, z>6.5. In early 2013, PS1 produced its first 3π catalog, marking a transformational leap forward in terms of depth and area. Already last year we discovered our first high-redshift quasar (Morganson et al 2012). Our aim is to discover a complete sample of 5.7 < z < 6.4 quasars in the 3π PS1 area, sensitive to a magnitude of z = 21.0, i.e. nearly a magnitude deeper than the SDSS quasar search. During 2013, we have discovered at least 8 additional high-redshift quasars (Banados et al. 2013, in preparation). The search and spectroscopic follow-up are just starting, and promise exciting results. Our survey has already increased the number of known z ~ 6 quasars by \\gtrsim 10 % and discovered the first bright z ~ 6 quasars in the Southern sky. In the near future, we will take full advantage of the PS1 y-band, pushing the survey to discover z ~ 7 quasars, unveiling the earliest quasars far back into the epoch of reionization.
Super massive black holes (SMBHs) seem to be the galaxies' beating hearts. While many observational discoveries support a close link between SMBH activity and the assembly of the host galaxy, the physical processes behind this interplay remain unclear. One of the most efficient way to constrain the physical models of AGN/galaxy co-evolution is to study the effect of accreting SMBHs in the galaxies that host them. Using the rich multi-band photometry in the COSMOS field we explore the host galaxy properties of a large, complete, sample of X-ray and spectroscopically selected AGN. Based on a two-components fit to their SED we derive rest-frame magnitudes, colors, stellar masses and star formation rates up to z~3. We find that the probability for a galaxy to host a black hole growing at any given specific accretion rate (the ratio of X-ray luminosity to the host stellar mass) is independent of the galaxy mass and follows a power-law distribution in LX/M. By looking at the normalization of such a probability distribution, we show how the incidence of AGN increases with redshift as rapidly as (1+z)4.2, in close resemblance with the overall evolution of the specific star formation rate (SFR). Although AGN activity and star formation appear to have a common triggering mechanism, we do not find any 'smoking gun' signalling powerful AGN influence on the global properties of their host galaxies. We also analyzed the dependence of optical obscuration on the host galaxy mass and SFR finding no relationship between the fraction of absorbed AGN and the stellar masses and SFR of their host galaxies, once objects of the same luminosity are compared. This result indicates that the physical properties of the medium responsible for optical obscuration in AGN are mainly determined by the environment in the small region close to the central SMBH, but are insensitive to the larger scale galactic conditions.
Current most sensitive surveys at soft X-ray (~0.5 --10 keV) energies by Chandra and XMM-Newton preferably sample AGN at high-redshift (z > 0.5). At low-redshift (z < 0.5), where AGN are supposed to be in their evolution end-stage, these sources are very sparsely sampled. The low-redshift universe is best fathomed at hard X--ray energies (> 15 keV) by the INTEGRAL and the Swift missions with their coded-mask telescopes IBIS/ISGRI and BAT respectively. These instruments have two major advantages: 1) they have a huge field of view, hence allowing to sample a large number of AGN at low-redshift; 2) they operate at energies above 15 keV, hence allowing detecting photons with enough power to efficiently pierce even through the Compton-thick torus of AGN. Estimates based on observations with PDS on board the BeppoSAX satellite predict that Compton-thick AGN should dominate over unabsorbed AGN in the local universe playing an important role in reproducing the shape and intensity of the cosmic X-ray background (CXB). However coded-mask detectors suffer from heavy systematic effects preventing them from reaching their theoretical limiting sensitivity. We overcome this limit with a new and alternative approach, which has been designed ad hoc to improve the sensitivity of hard X--ray surveys by using IBIS/ISGRI and BAT. Both telescopes are so close in design that their observations can be combined to obtain a more sensitive survey. The observations are combined with resampling, merging, and cross-calibration techniques. We are able to sample limiting fluxes of the order of ~3.3 times 10-12 erg cm-2 s-1 in the 18 - 55 keV energy range. This is called the SIX survey, that stands for Swift-INTEGRAL} X-ray survey. The SIX survey extends over a wide sky area of 6200 deg2 and it is used to obtain a persistent sample of faint AGN. The source number density (log N - log S) is a factor of 3 better than current parent surveys of BAT and IBIS/ISGRI alone. I will present a study of the evolution of AGN in the local universe discussing the X-ray luminosity function. The properties of the AGN circum-nuclear environment will be discussed checking the consistency with the AGN unification scheme. Also I will compare the results from the SIX survey to the results predicted for the NuSTAR survey. Finally preliminary results of the all-sky SIX survey are presented.
In order to fully understand the links between supermassive black holes and galaxy formation we must first have a complete view of AGN activity in the distant Universe. The demographics of Type 2 quasars, heavily obscured by gas and dust, are currently poorly understood at high redshift. In this work we present a sample of a large sample of high-redshift (1 < z < ~4) obscured quasars identified in the UKIDSS Ultra-Deep Survey (UDS). This unique survey has the deepest available 1-24 micron data available over ~1 deg2, allowing us to identify Type 2 AGN from their mid-IR excess combined with multi-wavelength SED fitting. We compare and contrast the host galaxies of Type 2 AGN with ordinary galaxies of equivalent stellar mass at the same epoch. We also present a study of local environments and large-scale structure, including the first reliable estimates of host halo mass for Type 2 quasars at z>~2.
We present the main results from a selection of optical spectra of Active Galactic Nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS) with detectable emission of forbidden high ionization lines (FHILs), better known as coronal lines. The presence of these lines gives evidence of a nuclear environment with very unique characteristics such as ionization potentials equal or greater than 100eV. Results continue indicating that FHILs are not observed in LINER type galaxies, nonetheless, for the first time a catalog of more than 300 unreported Seyfert 1 and Seyfert 2 type galaxies with FHILs is presented. Using these objects and another 80 more reported by Gelbord, Ekens, Osterbrock and others, we study the following line flux ratios and their distribution for Sy1 and Sy2 galaxies: [Fe VII]6087/[Fe x]6374, [FeX]6374/[FeXI]7892 and [NeV]3426/[FeVII]6087.
The physics of active black holes (BHs) is governed by three key parameters: their mass, spin, and accretion rate. Understanding the cosmic evolution of these parameters is crucial for tracing the evolution of the BHs to the epoch of their formation. We therefore select a unique AGN sample, in a narrow redshift range around z = 1.55, based on both SMBH mass and the Eddingtion ratio. We observed them with the X-Shooter instrument on the VLT, which provides high signal-to-noise spectra covering, at this redshift, the rest wavelength range ~1300 to 9200 A. This wide wavelength coverage allows us to study, in a single spectrum, many more emission lines (i.e., CIV 1550A through H-alpha), as well as a larger portion of the global AGN SED, than almost all previous samples. We currently have 30 quasars with BH masses ranging from ~10^7 to 10^9 M_solar and Eddington ratio from ~0.05 to 1.3. A central scientific goal is to identify emission-line profile dependencies on BH mass and the Eddington ratio, and, in particular, any deviation from pure Keplerian motion. A second key issue is related to the origin of the SED. With our unique sample, we can fit the SED over a wide range of wavelengths and can compare quasars with varying Eddington ratio, but constant BH mass. Our preliminary SED fitting shows already that a thin accretion disk model does not fit all the AGN in our sample well. Further SED fitting will confirm whether there is a transition between thin and thick accretion disks at an Eddington ratio of around 0.3, as predicted by models. Finally, our sample provides a unique benchmark to compare three mass determination methods, based on three (or four) different emission-line profiles (H-alpha, H-beta, MgII 2800A, and CIV 1550A). With single-epoch spectra that cover all of these emission lines, we can identify the most reliable methods and whether the mass determinations depend on the accretion disk and/or BH properties. In my talk, I will demonstrate several of these issues and compare our results with previously obtained samples.
I will present the results of recent studies on the co-evolution of galaxies and the supermassive black holes (SMBHs) using Herschel far-infrared and Chandra X-ray observations in the Boötes survey region. For a sample of star-forming galaxies, we find a strong correlation between galactic star formation rate and the average SMBH accretion rate in star-forming galaxies. Recent studies have shown that star formation and AGN accretion are only weakly correlated for individual AGN, but this may be due to the short variability timescale of AGN relative to star formation. Averaging over the full AGN population yields a strong linear correlation between accretion and star formation, consistent with a simple picture in which the growth of SMBHs and their host galaxies are closely linked over galaxy evolution time scales.
The Australia Telescope Large Area Survey (ATLAS) is the widest deep radio survey ever attempted, covering ~7deg2 across its two fields, the Chandra Deep Field South (CDFS) and the European Large Area ISO Survey South 1 Region (ELAIS-S1). ATLAS has extensive multiwavelength data, including optical, infrared and X-ray, to complement its ~15μJy rms 1.4 GHz radio data. At these faint radio flux densities, the proportion of AGN to star-forming galaxies (SFGs) is high, and there are likely many composite objects, which have both an AGN and ongoing star formation. In ATLAS, we estimate that the number of AGN is approximately 50%, and this proportion will change with decreasing flux density. To understand the relationship between the AGN and the host galaxy, we need to measure the contribution of the AGN to the total luminosity, and determine how this varies with the evolutionary stage of the galaxy. Here I present results exploring the AGN contribution to galaxies over cosmic time, through the use of different multiwavelength discriminants.
Before the launch of the Fermi satellite only two classes of AGN were known to generate relativistic jets and thus emit up to the gamma-ray energy range: blazars and radio galaxies, both hosted in giant elliptical galaxies. The first two years of observations by the Large Area Telescope on board Fermi confirmed that these two are the most numerous classes of identified sources in the extragalactic gamma-ray sky, but the discovery of variable gamma-ray emission from 5 radio-loud Narrow-Line Seyfert 1 galaxies revealed the presence of a possible emerging third class of AGN with relativistic jets. Considering that Narrow-Line Seyfert 1 are typically hosted in spiral galaxy, this finding poses intriguing questions about the nature of these objects, the onset of production of relativistic jets, and the cosmological evolution of radio-loud AGN. Here, we discuss the radio-to-gamma-rays properties of the gamma-ray emitting Narrow-Line Seyfert 1 galaxies in the context of the blazar scenario, in particular focusing on PKS 1502+036 and the two gamma-ray flaring sources PMN J0948+0022 and SBS 0846+513.
Completing the census of AGN in the Universe is the key to understanding the cosmic evolution of supermassive black holes (SMBH) and galaxies, and to resolving the spectrum of the X-ray background (XRB). However, a large population of AGN, especially the heavily obscured, Compton-thick AGN, are still missing from even the deepest X-ray surveys. The infrared spectra energy distribution (SED) of distant star-forming galaxies can reveal the presence of bright AGN activity. Using some of the deepest infrared, X-ray and radio data available in the GOODS fields, we identify a population of infrared bright quasars at redshift z~2, which are often missed in the X-ray band. Amongst these sources the number of obscured and heavily-obscured quasars is much higher than those previously found in several X-ray and optical selected samples. A unique view on these heavily-obscured quasars is now given at high energies by NuSTAR. I will present the first NuSTAR detection of a heavily obscured quasar at z~2. This source is a potential archetype of the heavily-obscured high-z AGN in which most of the black hole growth is happening, that can explain the mysterious missing fraction of the XRB.
The HeRGÉ (Herschel Radio Galaxy Evolution) project consists of a sample of 70 radio galaxies in the range 1 < z < 5.2. They benefit from continuous coverage from 3 to 870 μm with Spitzer, Herschel and sub-mm ground-based instruments (SCUBA, LABOCA). As a calorimeter, IR is an excellent proxy to estimate the contribution of both AGN and young stellar components, making radio galaxies perfect candidates to provide new insights into the relationship between AGN and their host galaxies. Drouart et al., (in prep) presents the results for the entire sample. We find a variation in LIRAGN related to either a variation of accretion efficiency or a deviation from the MBH-σ relation. Extending to optical/near-IR, old and young stellar populations can be identified by applying the evolutionary code PEGASE.3 to two z=4 radio galaxies (Rocca et al.,2013). Coupling the HeRGÉ catalogue with a variety of AGN models and PEGASE.3 allows for statistical results on the respective parameters of AGN torus, starburst and old stellar population. Implications for how AGN are related to their host galaxies will be discussed.
One of the remaining open issues in the context of the analysis of Active Galactic Nuclei (AGN) is the evidence that nuclear gravitational accretion is often accompanied by a concurrent starburst (SB) activity. What is, in this picture, the role played by the obscuring dust around the nucleus? Can the IR data provided by Spitzer and Herschel help us in extensively investigate both phenomena and, if so, how and with what limitations? Does the presence of an AGN have an impact in the mid- and far- IR properties of galaxies? Which are the effects of simultaneous AGN and SB activities in these same galaxies? In this talk I will present our contribution to the efforts of answering these questions. I will present the SED fitting tool we developed to derive simultaneously the physical properties of active galaxies and coexisting starbursts making the best use of Spitzer and Herschel mid- and far-IR observations. They both play a crucial role providing much stronger constraints on the models with respect to previous observing facilities. We applied the SED fitting procedure to a large sample of extragalactic sources representing the Herschel/Multi-tiered Extragalactic Survey (HerMES) population with IRS spectra with a plethora of multi-wavelength data (SDSS, Spitzer and Herschel/SPIRE) in order to study the impact of a possible presence of an AGN on the host galaxy's properties. I will finally present the main results obtained focusing, in particular, on the analysis on the star formation rate in connection to the presence of an AGN and comparing the properties of the hot (AGN) and cold (SB) dust components.
The CIDA Survey Variability Catalog (VVC-CIDA), contains photometric data of approximately seven million sources (V,R and I bands), corresponding to multi-epochs observations of 10 years (1998-2008). This survey was conducted with the QUEST camera in the 1 m Schmidt telescope at OAN (Observatorio Nacional de Venezuela). The variability survey covers roughly 1080 square degrees in the celestial equator (60 < RA < 150, -6 < DEC < 6). In this work we present the preliminary results of the search of QSO's in the CSV-CIDA. Our method allowed us to recover 10% of QSO reported by the SDSS-DR9, in an area where both surveys match. In addition, we show a preliminary sample of ~ 437 QSO's candidates in a region of the sky not well studied to date.
Mass ejection in the form of winds or jets appears to be as fundamental to quasar activity as accretion, and can be directly observed in many objects with broadened and blue-shifted UV emission and absorption features. A convincing argument for radiation pressure driving this ionized outflow - and thus the importance of the shape of the spectral energy distribution in shaping it - can be made within the dust sublimation radius. Beyond, radiation pressure is still important, but high energy photons from the central engine can now push on dust grains. This physics underlies the dusty wind model for the putative obscuring torus. In our implementation, the dusty wind is plausibly responsible for providing both the necessary obscuring medium to explain the ratio of broad-to-narrow-line objects and the mid-infrared emission commonly seen in quasar spectral energy distributions.
BL Lac objects are found in Fermi observations to be the most abundant emitters in gamma-ray band. However their parsec scale structure is poorly known since most of BL Lacs have a low radio power. Available VLBI surveys give information only of the few high power BL-Lac objects. To improve our knowledge of low radio power AGN and to analyse their radio and gamma properties, we selected a sample of BL Lacs at low redshift (z < 0.2) and no constrain on their radio or gamma-ray flux density. I will present here results from VLBA observations of this complete sample and I will discuss statistical properties. I will show the comparison between our results in radio band and Gamma-ray results for LAT objects. In particular I will discuss peculiar structures (steep spectrum and resolved components) found in a few low radio power sources.
The Atacama Cosmology Telescope (ACT) is a six-meter telescope in the Atacama Desert that observes simultaneously in frequency bands centered at 150, 220 and 270 GHz. ACT has surveyed an area of approximately 450 square degrees in the south (-55 deg) and approximately 500 square degrees along the equator. Most of the sources detected by ACT are blazars. I will present source counts and spectral indices as well as multi-wavelength properties determined by matching with external datasets. In addition to studying sources detected in the survey, we have used the ACT data to statistically study the millimeter properties of radio sources selected from low frequency (1.4 GHz) surveys.
Influence of the dark energy at small scales is considered. Interaction and energy exchange between ordinary matter and dark energy is proposed as a working hypothesis. It is obvious that the fact of accelerating cosmic expansion itself argues in favor of the energy exchange between ordinary matter and dark energy. Several observational facts are put into the base of this report to show that huge amounts of energy might accumulate any mass of ordinary matter if influenced by the Hubble flow. For example, if accepted that matter follows the space expansion at the scales under consideration, one can show that the energy passed to the matter is enough to generate cluster of galaxies for the Hubble time due to matter ejection mechanism.
Mid-infrared (MIR) quasar spectra exhibit a suite of emission features including high ionization coronal lines from the narrow line region (NLR) illuminated by the ionizing continuum, and hot dust features from silicates and graphite, as well as polycyclic aromatic hydrocarbons (PAH) features from star formation in the host galaxy. Few features are detected in most spectra because of typically low signal-to-noise ratios (S/N). We have generated high quality, average spectral composite templates for three luminosity bins. By generating spectral composites from over 180 IRS observations, we boost the S/N and reveal important features in the complex spectra. We detect high-ionization, forbidden emission lines in all templates, PAH features in all but the most luminous objects, and broad silicates and graphite in emission whose strength increases with luminosity. We find that the intrinsic quasar spectrum for all luminosity templates is the same; the differences in the spectra are due to host galaxy contamination in the low luminosity templates.
The Cosmological Evolution Survey (COSMOS) involves the largest contiguous region of the sky ever imaged by HST. It was motivated by the study of galaxy evolution and morphology but the combination of depth, breadth and extensive multiwavelength data makes it the best region in the sky for a comprehensive study of AGN. Using deep X-ray data in the field, over 800 AGN have been spectroscopically confirmed, and the survey has particular sensitivity to low black hole mass, low accretion rates, and high levels of obscuration. A limiting accretion rate of L/LEdd = 0.01 is seen, below which the flow may be advective. Analogs to the Milky Way black hole at z = 2 can be detected. A study of host galaxies suggests that the AGN triggering occurs on kiloparsec scales within the host. Fitting SEDs shows that the spectral components are predictable enough to efficiently select AGN below the limit of spectroscopy on large telescopes, extending this work to even lower black hole masses. The eventual goal is a complete census of intermediate mass black holes at redshifts 1-3, which is required to tell the complete story of the co-evolution of galaxies and black holes.
Using repeated imaging in five UV-to-IR photometric bands obtained by SDSS for over 30,000 spectroscopically confirmed quasars, we empirically characterize the optical continuum variability of quasars. The observed time lags span the range from a day to almost 10 years, and constrain quasar variability at rest-frame time lags of up to 4 years, and at rest-frame wavelengths from 1000 е to 6000 е. We find that a damped random walk model, defined by an exponential covariance matrix and parametrized by a characteristic timescale and an asymptotic variability amplitude, is statistically consistent with all the data. These two parameters scale with the luminosity, black hole mass, and rest wavelength, and are independent of redshift. The amplitude of variability is anti-correlated with the Eddington ratio, which suggests a scenario where optical fluctuations are tied to variations in the accretion rate. However, we find an additional dependence on luminosity and/or black hole mass that cannot be explained by the trend with Eddington ratio. The radio-loudest quasars have systematically larger variability amplitudes by about 30%, when corrected for the other observed trends, while the distribution of their characteristic timescale is indistinguishable from that of the full sample. We demonstrate that variability selection can deliver highly complete samples with reasonable purity (or efficiency): given an adequate survey cadence, photometric variability provides an even better method than color selection for separating quasars from stars.
Multiwavelength identification of AGN is crucial not only to obtain a more complete census, but also to learn more about the physical state of the nuclear activity (is it obscured? is it efficient? etc). I will demonstrate that a panchromatic strategy plays an especially important role when the host galaxies are star-forming. With a study far-IR selected galaxies at 0.3 < z < 1, and using AGN tracers in the X-ray, optical spectra, mid-infrared, and radio regimes, we find a twice higher AGN fraction than previous studies, thanks to the combined AGN identification methods and in particular the recent MEx diagnostic diagram. We furthermore find an intriguing relation between AGN X-ray absorption and the specific star formation rate (sSFR) of the host galaxies, indicating a physical link between X-ray absorption and either the gas fraction or the gas geometry in the hosts. As I will discuss, these findings have implications for our current understanding of both the AGN unification model and the nature of the black hole-galaxy connection.
There exist strong evidence supporting the co-evolution of central supermassive black holes and their host galaxies; however it is still under debate how such a relation comes about and whether it is relevant for all or only a subset of galaxies. A rich multi-wavelength dataset is available for the North Ecliptic Pole field, most notably surveyed by the AKARI infrared space telescope and with ancillary data covering the whole electromagnetic spectrum from the X-ray (Chandra), through the far-IR (Herschel-SPIRE), to the radio regime (WSRT). We want to tackle the role of activity in galaxies, in the form of accretion onto their supermassive black holes, within the frame of black hole and host galaxy co-evolution. In particular the star-formation properties of the host galaxies of radio-AGN is investigated together with the radio feedback mechanism, potentially responsible for the eventual quenching of star-formation. Using both broadband SED modeling and optical spectroscopy, the nuclear and host galaxy components of these sources are simultaneously studied as a function of their radio luminosity, bolometric luminosity, and radio-loudness. Here we present preliminary results concerning the AGN content of the radio sources in this field, while offering tentative evidence that jets are inefficient star-formation quenchers, except in their most powerful state.
I have combined data from sky surveys in the UV to the mid-IR, along with radio and X-ray data, to identify the most luminous QSOs in the Universe. The primary sky surveys were the Sloan Digital Sky Survey (SDSS) 7th Data Release QSO Catalog, which provides unambiguous broad-line QSO classification and robust redshifts, and the Wide-field Infrared Survey Explorer (WISE) mid-IR catalog, because a large percentage of QSO bolometric luminous emerges in the IR. Out of the 100,000 SDSS/WISE QSOs, we find 140 ( < 0.2%) with bolometric luminosity greater than 2x1014LΘ, with redshifts ranging from about 1.7 to 5. The most luminous QSO found has Lbol ≈ 7x1014 LΘ. Merger-based galaxy evolution models predict that the host galaxies of such sources at peak QSO luminosity are undergoing a short-lived phase of extreme AGN feedback and massive star-formation activity after a major merger. Upcoming sub-mm observations with the new Atacama Large Millimeter/Sub-millimeter Array (ALMA), for a subset of the sample, will soon reveal crucial host galaxy properties of this unique sample.
The four year X-ray all-sky survey (eRASS) of eROSITA telescope aboard the Spektrum-Roentgen-Gamma satellite will detect ~3 million AGN with a median redshift of z ≈ 1 and typical luminosity of L0.5-2.0 keV ~ 1044 erg s-1. We show that this unprecedented AGN sample, complemented with redshift information, will supply us with outstanding opportunities for large-scale structure research. For the first time, detailed redshift and luminosity resolved studies of the bias factor for X-ray selected AGN will become possible. The eRASS AGN sample will not only improve the redshift and luminosity resolution of these studies but will also expand their luminosity range beyond L0.5-2.0 keV ~ 1044 erg s-1, thus making possible direct comparison of clustering properties of luminous X-ray AGN and optical quasars. These studies will dramatically improve our understanding of AGN environment, triggering mechanisms, growth of super-massive black holes and their co-evolution with dark matter halos. The eROSITA AGN sample will become a powerful cosmological probe. It will make possible detection of baryonic acoustic oscillations (BAOs) for the first time with X-ray selected AGN. With the data from entire extragalactic sky, BAO will be detected at a ≥~10σ confidence level in the full redshift range and with ~8σ confidence in the 0.8 < z < 2.0 range, currently uncovered by any existing BAO surveys. In order to exploit the full potential of the eRASS AGN sample, photometric and spectroscopic surveys of large area and a sufficient depth will be needed.
We systematically search for discrete absorption events in the vast archive of the Rossi X-ray Timing Explorer. This includes dozens of nearby type I and Compton-thin type II AGN and covers timescales from days to over a decade for individual objects. We are sensitive to discrete absorption events due to clouds of full-covering, neutral or mildly-ionized gas with columns 1022-25 cm-2 transiting the line of sight. We detect 13 eclipse events in 8 objects, roughly tripling the number of previously published events from this archive. Despite sensitivity to events with NH up to 1024-25 cm-2, we measured no Compton-thick eclipses in our sample. Peak column densities span 2.5 - 19 x 1022 cm-2. Event durations span hours to months. We infer the clouds’ distances from the black hole, assuming Keplerian motion, to span 0. 2 - 80 x 104 Schwarzschild radii. We find no statistically significant difference between the individual cloud properties of type I and II objects. The presence of eclipses in both type Is and IIs argues against sharp-edged cloud distributions. The type II AGN show a level of “base-line” X-ray absorption that is consistent with being constant over timescales from 0.6 to 8.4 yr. This can either be explained by a homogeneous medium, or by X-ray-absorbing clouds that each have NH << 1022 cm-2. Considering the "selection function" of the monitoring, we derive the probability of cloud occultation events. Finally, we derive the first X-ray statistical constraints for clumpy-torus models.
Until recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G; Murphy et al., 2010); a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete sample of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique sample of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole. In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected sample, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large sample of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.
One of the most important features in active galactic nuclei (AGN) is the variability of their emission. Variability has been discovered at X-ray, UV, and radio frequencies on time scales from hours to years. Among the AGN family and according to theoretical studies, Low-Ionization Nuclear Emission Line Region (LINER) nuclei would be variable objects on long time scales. Our purpose is to investigate spectral X-ray variability in LINERs and to understand the nature of these kinds of objects, as well as their accretion mechanism. Chandra and XMM-Newton public archives were used to compile X-ray spectra of LINER nuclei at different epochs with time scales of years. To search for variability we fit all the spectra from the same object with a set of models, in order to identify the parameters responsible for the variability pattern. We also analyzed the light curves in order to search for short time scale (from hours to days) variability. Whenever possible, UV variability was also studied. We found that long term spectral variability is very common, with variations mostly related to hard energies (2-10 keV). These variations are due to changes in the soft excess, and/or changes in the absorber, and/or intrinsic variations of the source. Short time scale variations during individual observations were not found. Our analysis confirms the previously reported anticorrelation between the X-ray spectral index and the Eddington ratio, and also the correlation between the X-ray to UV flux ratio and the Eddington ratio. These results support an Advection Dominated Accretion Flow (ADAF) as the accretion mechanism in LINERs.
About one third of the gamma-ray sources detected by Fermi have still no firmly established counterpart at lower energies. Here we propose a new approach to find candidate counterparts for the unidentified gamma-ray sources (UGSs) based on the 325 MHz radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the northern hemisphere. First we investigate the low-frequency radio properties of blazars, the largest known population of gamma-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO VLA Sky survey (NVSS). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in literature to look for infrared and optical counterparts of the gamma-ray blazar candidates selected with the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research we identify 23 new gamma-ray blazar candidates out of 32 UGSs investigated. I will also present the first analysis of very low frequency radio emission of blazars based on the recent Very Large Array Low-Frequency Sky Survey (VLSS) at 74 MHz. I show that blazars present radio flat spectra when evaluated at 74 MHz, about an order of magnitude in frequency lower than previous analyses. The implications of these findings in the contest of the blazars -- radio galaxies connection will be discussed.
The Bright Ultra-hard XMM-Newton Survey (BUXS) is the largest, among the existing XMM-Newton and Chandra surveys, flux-limited sample of bright sources selected at ultra-hard X-ray energies (4.5-10 keV). BUXS includes 258 objects detected over a total sky area of 44.43 deg2 of which 252 are spectroscopically identified, 145 as type-1 AGN and 107 as type-2 AGN. The bright flux limit ensures that we can derive accurate X-ray properties such as absorption and intrinsic luminosities from high-quality X-ray spectra (> few hundred counts). Surveys such as BUXS are a unique resource to probe the bulk of the Universe's accretion power missed by deep surveys reaching for the most distant Universe. BUXS has full coverage at MIR wavelengths with NASAS's Wide-field Infrared Survey Explorer (WISE) with a MIR detection rate of 98.8%. We have used the rich multiwavelength data set available for BUXS to define an mid-infrared (MIR) technique (infrared AGN wedge) for selection of luminous AGN using the 3.4, 4.6, and 12 um bands of the WISE survey. We have quantified the host galaxy dilution effect on the completeness of the technique as a function of luminosity for both type-1 and type-2 AGN demonstrating that our technique is highly reliable and it can efficiently trace highly luminous AGN up to redshift~1-2. To address whether our technique can identify the heavily obscured and even Compton-thick AGN missed in X-rays as well as to characterize the AGN populations identified, we have studied the WISE properties for the largest catalogue of type 2 quasars (QSO2s) in the literature from the Sloan Digital Sky Survey (SDSS). The catalogue contains 887 sources at z < 0.83 selected based on their high [OIII]5007 line luminosities. Such a selection should be relatively unbiased for heavily obscured AGN. At high luminosities, our technique is able to identify SDSS QSO2s with an efficiency comparable to that for X-ray selected type-2 AGN. Furthermore, the fraction of luminous SDSS QSO2 identified as Compton-thick candidates in our infrared AGN wedge is consistent with the fraction of all SDSS QSO2s in that zone. We found a trend where higher (line of sight) absorption might be associated with redder WISE infrared colours. However for the SDSS QSO2s it is not the possible presence of Compton-thick obscuration that determines their red WISE colours but the properties of their host galaxies. Even at high luminosities MIR selection techniques can be biased against AGN with massive host galaxies. Our results fully support that our technique is able to identify luminous heavily obscured and even Compton-thick AGN at z < 1 with a high efficiency (>65%).
When galaxies merge, gas accretes onto both central supermassive black holes. Thus, one expects to see dual active galactic nuclei (AGNs) in a fraction of galaxy mergers. Candidates for galaxies containing dual AGNs have been identified by the presence of double-peaked narrow [O III] emission lines and by high spatial resolution images of close galaxy pairs. 30% of double-peaked narrow [OIII] emission line SDSS AGNs have two spatial components within a 3” radius. However, spatially resolved spectroscopy is needed to confirm these galaxy pairs as systems with double AGNs. With the Keck 2 Laser Guide Star Adaptive Optics system and the OSIRIS near-infrared integral field spectrograph, we obtained spatially resolved spectra for SDSS J09527.62+255257.2, confirming that it contains a Type 1 and a Type 2 AGN separated by 4.8 kpc (=1.0"). We performed similar integral field and long-slit spectroscopy observations of more spatially separated candidate dual AGNs and will report on the varied results. By assessing what fraction of radio-quiet double-peaked emission line SDSS AGNs are true dual AGNs, we can better constrain the statistics of dual AGNs and characterize physical conditions throughout these interacting AGNs.
Binary supermassive black holes (SMBH) are expected to form in the course of a merger event; however, very few SMBH pairs have been detected and the role they play in the growth of SMBHs and the triggering of nuclear activity is still under debate. With the aim of increasing the number of detected binary SMBHs and understanding their contribution to the formation and evolution of galaxies, we first study systems showing evidence of a past black hole (BH) merger: we present evidence of merger-triggered AGN activity from the study of the SMBH mass and starburst activity in X-shaped radio galaxies, a type of active galaxies with a very peculiar jet morphology suggested to be the result of a merger event. We then turn our attention to ongoing galaxy mergers and perform a photometric fit to a sample of double-nucleus disk galaxies, which allows us to derive the luminosity of the nuclei and their relative separation. We find that most of the sources have projected binary distances < 4 kpc and that they are possibly in the post-merger state of a major merger. The luminosity of both the primary and the secondary nuclei decreases with the binary distance, which can be explained by a reduction of the accretion onto the SMBHs as expected from galaxy evolution models. The results obtained thus support that mergers must play an important role in galaxy assembly. We also identify a sample of 19 double-nucleus disk galaxies in which the two nuclei are physically separated by < 1 kpc, and find 13 peculiar sources that do not seem to follow the typical black hole-galaxy scaling relations.
Theory has shown that in young and compact extragalactic radio sources lobes and jets can produce gamma-ray flux, via Compton scattering of different seed photons, to levels potentially detectable by Fermi-LAT. Being contributed only by the non-thermal emission, the gamma-ray band is important to ascertain the origin of the whole high-energy (X- to gamma-ray) output in this class of sources. This is a crucial aspect for our understanding of radio sources' evolution and the feedback mechanism with the host galaxy during the initial stage of the source expansion. We report the results of our investigation on the gamma-ray emission of a sample of young radio sources, already observed in the X-rays, using ~4 yrs of Fermi-LAT data.
We examine properties of galaxies and quasars with steep low-frequency radio spectra from the UTR-2 catalogue. The number of these objects have the non-thermal X-ray emission due to the inverse Compton scattering of radio photons of the microwave background by relativistic electrons. So, it is possible to estimate the magnetic field strength and the relation of energies of the magnetic field and relativistic particles, independently. As we received the determined values of magnetic field strength are near one order less than those at the well-known energy equipartition condition. We conclude from the obtained energy relation that the energy of relativistic particles prevails over the energy of magnetic field in the galaxies and quasars with steepness radio spectra.
We select 180 pairs with dV < 800 km s(-1) and Dp < 60 kpc containing Markarian (MRK) galaxies. We study the dependence of galaxies integral parameters, star-formation (SF) and active galactic nuclei (AGN) properties on kinematics of pairs, their structure and large-scale environments. Following main results were obtained. Projected radial separation Dp between galaxies correlates with the perturbation level P of the pairs. Both parameters do not correlate with line-of-sight velocity difference dV of galaxies. Dp and P are better measures of interaction strength than dV. The latter correlates with the density of large-scale environment and with the morphologies of galaxies. Both galaxies in a pair are of the same nature, the only difference is that MRK galaxies are usually brighter than their neighbors in average by 0.9 mag. Specific star formation rates (SSFR) of galaxies in pairs with smaller Dp or dV is in average 0.5 dex higher than that of galaxies in pairs with larger Dp or dV. Closeness of a neighbor with same and later morphological type increases the SSFR, while earlier-type neighbors do not increase SSFR. Major interactions/mergers trigger SF and active galactic nuclei more effectively than minor ones. The fraction of AGNs is higher in more perturbed pairs and pairs with smaller Dp. AGNs typically are in stronger interacting systems than star-forming and passive galaxies. There are correlations of both SSFRs and spectral properties of nuclei between pair members.
Radiatively inefficient, hot accretion flows are widely considered as a relevant accretion mode in low-luminosity AGNs. We present a refined model of spectral formation in such flows with a fully general relativistic description of both the radiative (leptonic and hadronic) and hydrodynamic processes, as well as using an exact treatment of global Comptonization. We derive the radiative efficiency and the spectral energy distribution as functions of the black hole spin and we apply these results to modeling the luminosity—X-ray slope correlation observed in LL AGNs. Hadronic processes in hot flows lead to substantial gamma-ray emission. We study the expected X-ray to gamma-ray luminosity ratios. We point out that accretion flows may contribute significantly to the persistent gamma-ray emission observed in low emission states of Cen A and M87.
The WISE satellite mission has collected an unprecedented infrared dataset. Its four photometric filter bandpasses at 3.4, 4.6, 12 and 22 micron enable studies of dust emission from various astronomical sources, including quasars and Active Galactic Nuclei (AGN). With its sensitivity up to 1000 times better than previous missions (e.g. IRAS) and a spatial resolution between 6 and 12 arcsec, WISE measured brightness and colors on hundreds of millions of point sources, and among them many tens of thousands of AGN. Using a large cross-matched sample of previously classified SDSS objects, we define reliable selection criteria for type-1 AGNs with dust torus emission. Aided by our large database of CLUMPY torus models (Nenkova et al. 2008a,b), we identify the ranges of model parameter values supported by WISE observations, and derive likely properties of AGN tori in general. Unlike previous studies, this AGN torus characterization has been performed with high statistical significance thanks to the unprecedentedly large sample size. For the very first time we are now able to predict the number of observable type-2 AGN from an observed sample of unobscured type-1 objects. We also derive color selection criteria for type-2 sources using best-fit models for confirmed type-1 sources but with complementary viewing angles (i.e. preferentially edge-on lines of sight). We find that type-2 objects are type-2 precisely because they are intrinsically more likely to be observed along optically obscured lines of sight: type-1 and type-2 AGN have significantly different dust covering factors and line-of-sight photon escape probabilities. Finally, using recent studies of BL Lac objects, we show that in certain configurations CLUMPY torus models are compatible with the relatively blue WISE colors seen in these sources.
We present results from a project focused on searching optical microvariabilty (also known as "intra-night" variability) in type 2 - obscured - quasars. Optical microvariability can be described as very small changes in the flux, typically in the order of hundredths of magnitude, which can be observed on timescales of hours. Such studies have been so far conducted for samples of blazars and type 1, unobscured, AGNs, where the optical microvariability has been detected with success. We have focused on obscured targets which pose a challenge to the AGN standard model. For our study, we have observed a sample of three bright (g mag < 17) type 2 quasar, based on the catalog of type 2 quasars from SDSS of Reyes et al. (2008). The observations were carried out with the 1.5 meter telescope at San Pedro Martir observatory in Mexico. The sample was observed during an observation period of four days in Johnson’s V filter, resulting in at least two continuous intervals of observations per target during the observational run. We have obtained differential light curves for our sources as well as for the comparison stars. They were analyzed using one-way analysis of variance statistical test (ANOVA), which has been repeatedly used in the past for studies of unobscured targets. Based on the results from the statistical analysis, we show that at least two out of three observed targets appear to be variable on time scales of hours. So far, this is the first study which confirmed existence of optical microvariability in type 2 quasars.
High resolution integral field spectroscopy allows us to map the inner regions of AGN host galaxies and the dynamics of the gas and stars close to the black hole. In this contribution I will present a unique view of the galaxy MCG-6-30-15, observed for the first time with SINFONI on the VLT and at the best spatial resolution (0.1 arcsec) so far. MCG-6-30-15 is a Narrow-Line Seyfert 1 galaxy, well known for its X-ray properties. Due to the multi-wavelength data available and its AGN properties, this galaxy provides an important test case to probe the host galaxy properties of NLSy1 galaxies and to study black hole fuelling at higher mass accretion rates. I will present the results from our H-band integral field data analysis of this galaxy. In this work, we were able to model and remove the AGN contribution and hence probe the galaxy's stellar and gas kinematics at the best spatial resolution up to now. We discovered a counter-rotating stellar core and extended [Fe II] emission in the central 200 pc region. Using the stellar and ionised gas properties and the observed dynamics, we explored the relation between the counter-rotating core formation and the black hole fuelling, and set constraints on the mass of the black hole. Based on these results, I will then discuss the importance of this source to future larger studies of black hole fuelling.
Supermassive black holes (BHs) live at the heart of essentially all massive galaxies with bulges, power AGN, and are thought to be important agents in the evolution of their hosts. Observations of high-redshift quasars demonstrate that supermassive BHs must start out with masses considerably in excess of normal stellar-mass BHs. However, we do not know how the initial "seed" BHs formed in the early Universe, how massive they were originally, or what types of galaxies they formed in. While direct observations of distant seed BHs and their hosts in the infant Universe are unobtainable with current capabilities, models of BH growth in a cosmological context indicate that present-day dwarf galaxies can place valuable constraints on seed masses and distinguish between various seed formation mechanisms at early times. Using optical spectroscopy from the SDSS, we have systematically assembled the largest sample of dwarf galaxies hosting AGN to date. These dwarf galaxies have stellar masses comparable to the Magellanic Clouds and contain some of the least-massive supermassive BHs known. I will present results from this study and discuss our ongoing efforts to find additional examples of AGN in dwarfs and help constrain theories for the formation of the first seed BHs at high redshift.
A large fraction of the AGN output power is emitted in the X-rays, in a region very close to the supermassive black hole (SMBH). The most distinctive feature of the X-ray spectra of AGN is the iron Kα line, often observed as the superposition of a broad and a narrow component. While the broad component is found in only ~ 35-45% of bright nearby AGN, the narrow component has been found to be ubiquitous. The narrow Fe Kα line is thought to be produced in the circumnuclear material, likely in the molecular torus. Given its origin, this feature is possibly the most important tracer of neutral matter surrounding the SMBH. One of the most interesting characteristics of the narrow Fe Kα line is the decrease of its equivalent width with the continuum luminosity, the so-called X-ray Baldwin effect (Iwasawa & Taniguchi 1993). This trend has been found by many studies of large samples of type-I AGN, and very recently also in type-II AGN (Ricci et al. 2013c, submitted to ApJ). The slope of the X-ray Baldwin effect in type-II AGN is the same of their unobscured counterparts, which implies that the mechanism at work is the same. Several hypothesis have been put forward in the last decade to explain the X-ray Baldwin effect: i) a luminosity-dependent variation in the ionisation state of the iron-emitting material (Nandra et al. 1997); ii) the decrease of the number of continuum photons in the iron line region with the Eddington ratio, as an effect of the well known correlation between the photon index and the Eddington ratio (Ricci et al. 2013b, submitted to MNRAS); iii) the decrease of the covering factor of the torus with the luminosity (e.g., Page et al. 2004, Ricci et al. 2013a A&A 553, 29) as expected by luminosity-dependent unification models (e.g., Ueda et al. 2003). In my talk I will review the main characteristics of the narrow Fe Kα line, and present the results of our recent works aimed at explaining the X-ray Baldwin effect using iron-line emitting physical torus models (Ricci et al. 2013a,b), and at understanding the origin of the Fe Kα line (Ricci et al. 2013c). I will focus in particular on the importance of the Fe Kα line as a probe of the evolution of the physical characteristics of the molecular torus with the luminosity.
We have undertaken a spectroscopic survey of luminous AGNs and quasars selected in the mid-infrared from Spitzer IRAC surveys. Mid-infrared selection is much less biased with respect to obscuration than optical techniques, and hence enables the discovery of obscured quasars as well as normal, unobscured ones. Our survey is designed to include brighter 24 micron sources over wider areas and also to go to much lower fluxes limits in more limited spatial regions to allow us to disentangle dependences on redshift and luminosity. We have used 4m class telescopes to obtain spectra of the brighter 24 micron targets (targeting high luminosity objects at low z), and 8m class telescopes to identify lower luminosity high redshift obscured quasars by targeting the fainter 24 micron targets. We have therefore been able to construct luminosity functions for both obscured and unobscured quasars selected in the same way and covering similar redshifts and luminosities.
In the era of deep, large-area far-infrared (FIR) surveys from the Herschel Space Telescope, the bulk of the star-formation in distant galaxies, once hidden by dust, is now being revealed. The FIR provides probably the cleanest view of star-formation in the host galaxies of Active Galactic Nuclei (AGN) over cosmic time. We report results from studies of the relationships between star-formation, AGN activity and AGN obscuration out to z=2.5, which employ some of the deepest FIR and X-ray datasets currently available, while spanning orders of magnitude in the dynamic range of AGN properties. We highlight the role of gaseous supply in modulating both SF and AGN activity without necessarily implying a direct causal connection between these phenomenon. The role of starburst- or major merger-fueled AGN activity at low and high redshifts is discussed in the context of our results.
We analyze a sample of 30,000 nearby obscured AGNs with optical spectra from the Sloan Digital Sky Survey and mid-IR photometry from the Wide-field Infrared Survey Explorer. Our aim is to investigate the host galaxy properties in AGNs where the nuclear activity level is indicated by the mid-IR luminosity, and to compare the results to previous studies, which have used the [OIII] emission line as the main black hole activity indicator. We first carry out a systematic study of how the mid-IR colours of AGN hosts vary as a function of age-sensitive 4000 Å break strength and optical "Eddington parameter" L[OIII]/MBH. We find that the [3.4] - [4.6] micron colour has weak dependence on Dn(4000), but strong dependence on L[OIII]/MBH. We then use a "pair-matching" technique to subtract the 4.6 micron stellar emission contributed by the host galaxy. Intrinsic 4.6 micron AGN luminosities can be recovered for most Seyferts, but only statistically for LINERs. By combining our sample of Seyferts with a sample of type 1 AGN and quasars at z < 0.7 from the SDSS, we show that the [OIII] and 4.6 micron luminosities correlate roughly linearly over 4 orders of magnitude, but with substantial scatter. We also compare the partition functions of the total integrated 4.6 micron and [OIII] line luminosities from Seyferts as function of a variety of host galaxy properties, finding that they are identical. We also examine [OIII] and 4.6 micron partition functions for the sub-population of LINERs that still have significant 4.6 micron emission after subtraction of the host galaxy, finding that they are also identical. We conclude, therefore, that [OIII] as an AGN indicator shows no particular biases as compared to the 4.6 micron luminosity obtained from WISE. Our results also demonstrate that some LINERs do fit in with the expectations of the simple Unified Model. By investigating the environment of the Seyfert galaxies, we find neighbour counts excess around the IR-bright Seyferts, implying a link between the IR emission and the galaxy interactions.
The Fermi-LAT has accumulated a large sample of blazars with known flux and spectral index. However, since blazars with harder spectra can be detected to lower fluxes with the LAT, the observed bi-variate flux-index distribution is severely truncated at low fluxes and softer spectra. Previously we have used the non-parametric method developed by Efron and Petrosian (EP) to correct the Fermi data for this truncation and obtained the true mono-variate distributions of spectral index and flux (Singal et al. 2012, ApJ, 753, 45). By now many of the FSRQ blazars are identified with optical AGN and their redshifts measured or obtained from archives (M. Shaw et al., 2012, ApJ, 748, 49). With the redshifts we can now calculate the FSRQ blazar luminosities and from the tri-variate luminosity-index-redshift distribution determine the redshift evolutions of the luminosity and photon index and their distributions. The EP method can be generalized to this three dimensional case (as we done for SDSS quasars; Singal et al. 2013, ApJ, 764, 43). In this talk we will present the results from this analysis, which will allow us to compare the density and luminosity evolution of FSRQ blazars with other AGNs. In addition, we can determine a more reliable estimate of the total contribution of FSRQs to the extragalactic gamma-ray background.
We use spectra from the SDSS to study the signatures of nuclear activity over cosmic time, dividing the samples in redshift and mass bins, and using various diagnostic diagrams. A redshift evolution clearly emerges from the analysis of our diagrams.
I present recent ALMA, Hubble , and Chandra results that advance our understanding of AGN heating and intracluster medium cooling in the central giant ellipticals of cool core galaxy clusters. Stunning new HST FUV continuum imaging reveals star formation on 30 kpc scales in clumpy, filamentary, and disk-like distributions, many of which exhibit strong evidence for both jet-triggered star formation as well as spatially structured residual cooling channels stemming from the ambient hot X-ray atmosphere. Highlights from recent Chandra results include three unique signatures of radio-mode AGN feedback, including what may be the first direct observational evidence in support of buoyant X-ray cavity heating models invoked to inhibit cooling flows at late epochs. Finally, I discuss exciting recent and forthcoming ALMA observations of the morphologically and kinematically complex cold gas reservoirs in cool core brightest cluster galaxies. Cool core clusters are thought to harbor the only observable, low-redshift analogues of cooling processes thought to drive galaxy growth at early epochs. The results I present here are therefore relevant not only for cool core physics, but for galaxy evolution as a whole.
In this talk I will present the results from our work using a large, uniform, and highly spectroscopically complete to faint X-ray flux limits Chandra sample (in the CDFN, CLASXS, and CLANS fields) to compare AGN optical spectral types with their X-ray spectral properties. We confirm that there is significant overlap of the X-ray spectral properties for the different optical spectral types. For example, broad-line AGNs are expected to be unobscured and hence X-ray soft, yet we find ~20% have hard X-ray spectral slopes. Non-broad-line AGNs are expected to be obscured and hence X-ray hard, yet we find ~30% have soft X-ray spectral slopes. Thus, one cannot use the X-ray spectral classifications and the optical spectral classifications equivalently. We also confirm the dependence of optical spectral type on X-ray luminosity, and for z < 1, we find a similar luminosity dependence of X-ray spectral slope. However, this dependence breaks down at higher redshifts due to the highly redshift-dependent nature of the X-ray spectrum. I will also present the results from our multiwavelength study of BPT-composites, galaxies that lie between the Kauffmann et al. (2003) empirical cut and the Kewley et al. (2001) theoretical prediction for where star formation and AGN dominated sources lie in the Baldwin, Phillips, and Terlevich (BPT) emission line diagnostic diagram. BPT-composites comprise 20% of the emission line galaxy population, but it has been unclear, until recently, whether to include or exclude them from AGN samples. Our study makes a strong case for inclusion: the majority of BPT-composites appear to harbor obscured AGN activity (based on their [NeIII], [OII], g-z color information, and stacked X-ray and infrared emission). I will present our results and discuss the implications for AGN-galaxy evolution studies.
The intriguing existence of 'True'-Seyfert 2s have open a debate on the validity the unified model of active galactic nuclei (AGN). These objects, also called 'Naked'-AGN, seem to lack a broad line region according to their optical spectra, though their unabsorbed X-ray emission is typical of Seyfert 1 sources. Here, we present the analysis of high resolution near-infrared integral field observations of two 'True'-Seyfert 2 candidates. Based on the stellar kinematics, we estimate the black hole masses in MBH ~ 105 MΘ. This result, together with their bolometric luminosities Lbol ~ 1042 erg s-1, indicate that the broad lines must be faint and very narrow (FWHM ~ 500 km s-1). At least one of the sources shows a broad Brγ emission consistent with these predictions. Our results favor the unified model in the cases of high accretion rates, and stress the necessity of a multiwavelength approach to unveil the nature of 'Naked'-AGN.
The recently published ZORROASTER catalogue is being expanded into what will eventually be a complete list of known 'nearby' (z < 0.1) AGN, with optical spectral images, detailed spectral descriptors and waveband-specific flux ratios included where available. The first version of ZORROASTER contained 2843 entries characterised by confirmed or previously suspected broad H-beta emission, and 1000 spectral images. The 2nd version of ZORROASTER is to be released during the conference, and will (in addition to serendipitous updates) include all z < 0.1 objects from the list of Markarian. Activity classes and spectral descriptions of Markarian objects have been reviewed, and comparisons of flux ratios derived from the 100 ZORROASTER wavelength-specific pass bands are presented for those Markarian AGN for which Sloane Digital Sky Survey spectra exist. The value of the improved parameterizations and classifications of the Markarian objects on AGN studies, and the implications on some past investigations based on the Markarian lists, are briefly discussed.
I’ll discuss the correlation of masses of compact nuclear objects in S-S0 galaxies (supermassive black holes and nuclear clusters) with the observed properties of their parent galaxies: inner mass density, velocity of rotation, dynamical mass, luminosity and colors of stellar population. In particular, it will be demonstrated that galaxies belonging to the ⌠red sequence and the "blue sequence differ by their compact nuclear objects’ properties. The results enable to put some constraints on the possible scenarios of their evolution.