Over the last decade, quasar sample sizes increased from several thousand to over a hundred thousand, thanks mostly to SDSS imaging and spectroscopic surveys. LSST, the next-generation optical imaging survey, will provide hundreds of detections for a sample of more than ten million quasars with redshifts up to about seven. I will review optical quasar selection techniques, with emphasis on methods based on colors, variability properties and astrometric behavior.
I will discuss photoionization models for AGN, including Seyfert and LINERs. These photoionization models can be used to derive emission-line diagnostics for AGN that can determine the properties of the AGN and surrounding ISM, including the relative AGN contribution to the EUV radiation field, the hardness of the AGN radiation field, the ionization state of the gas, and the metallicity of the narrow-line region. I will show how the AGN emission-line diagnostics are expected to change with redshift. Finally, I will present our latest application of these models to wide integral field spectroscopy to separate starburst and AGN contributions in composite galaxies.
Markarian survey (or the First Byurakan Survey, FBS) was the first systematic survey for active galaxies and was a new method for search for such objects. Until now, it is the largest objective prism survey of the sky (17,000 sq. deg). It was carried out in 1965-1980 by B.E. Markarian et al. and resulted in discovery of 1515 UV-excess (Markarian) galaxies. They contain many active galaxies, as well as powerful gamma-, X-ray, IR and radio sources (Mrk 180, 231, 421, 501, etc.), BCDGs (Mrk 116) and interacting/merging systems (Mrk 266, 273, etc.). They led to the classification of Seyfert galaxies into Sy1 and Sy2 and the definition of Starbursts (SB). Several catalogs of Markarian galaxies have been published (Mazzarella & Balzano 1986; Markarian et al. 1989, 1997; Bicay et al. 1995; Petrosian et al. 2007). Markarian survey also served as a basis for search for UVX stellar objects (including QSOs and Seyferts), late-type stars and optical identification of IR sources. At present the survey is digitized and DFBS database is created. I will review about the main characteristics of Markarian survey, its comparison with other similar surveys and the importance of Markarian galaxies in modern astrophysics.
Obscured AGN may correspond to a substantial fraction of the supermassive black hole growth rate. I will present new surveys with the SCUBA-2 instrument on the James Clerk Maxwell Telescope of the Chandra Deep Fields and discuss whether we can distinguish obscured AGN in hard X-ray and radio selected samples using submillimeter observations.
The final 800 sq deg of sky covered by FIRST was observed with the new, improved JVLA. The data were split between two bandpasses at 1335 and 1730 MHz and included all four Stokes parameters, thus allowing both spectral and polarimetric results. The lower frequency bandpass data were considered part of FIRST and are available through the FIRST website (http://sundog.stsci.edu/). Here we present the higher frequency bandpass data as pertain to AGN. Foremost, we present spectral index results for the 5000 quasars with spectroscopic redshifts and the 50000 quasars with photometric redshifts that fall in the survey area. The spectral indices are analyzed as a function of redshift and optical properties both for quasars detected above the 1 mJy limit and, via image stacking, for quasars at flux densities down to 10 uJy.
Very Long Baseline Interferometry (VLBI) provides the highest angular resolution achievable in astronomy, to sub-milliarcsecond scales. For radio loud AGNs, this offers the unique opportunity to directly image and monitor the fine details of the jet structure, approaching the event horizon in the nearest and most supermassive black holes, like in M87. In this talk, I will present results from recent VLBI monitoring projects on two remarkable radio and high energy sources: the radio galaxy M87 and the BL Lac object Mrk421. In M87, we reveal and follow the evolution of the core and the jet feature HST-1; we reveal superluminal motion of components within HST-1, with a possible connection between ejection of new such components and the occurrence of very high energy flares. In Mrk 421, we present a detailed analysis of the jet structure in total intensity and polarization through the whole 2011, during which a multi-wavelength campaign took place. We reveal flux density variability but no significant changes in the jet structure. Estimates on the physical parameters for both sources are given (Doppler factor, viewing angle, magnetic field, etc.).
The space element of the ground-space very long baseline (VLB) interferometer RadioAstron is a 10-meter radio telescope Spektr-R which was successfully launched in 2011. It covers four frequency bands from 0.3 to 25 GHz and provides baselines up to 350,000 km. This allows to study space objects with a resolution as high as about 10 microarcseconds. Fringes are found at all four bands of 92, 18, 6, and 1.3 cm. Science observations are ongoing. Early results of the RadioAstron AGN survey at extreme angular resolutions will be presented in the talk. In particular, AGN core emission is successfully detected at interferometer baselines up to 7.6 GLambda (or fringe spacing 27 microarcseconds) which is the current VLBI record. High radio brightness of AGN cores is found significantly above the known inverse-Compton limit. Implications to AGN jet emission models will be discussed. First results of RadioAstron space VLBI imaging of AGN jets will be also presented.
We present our very recent results on the sub-mJy radio source populations at 1.4 GHz based on the Extended Chandra Deep Field South VLA survey, which reaches ~ 30 microJy, with details on their evolution and luminosity functions. The sub-mJy radio sky turns out to be a complex mix of star-forming galaxies and radio-quiet AGN evolving at a similar, strong rate; non-evolving low-luminosity radio galaxies; and declining radio powerful (P > 1024 W/Hz) AGN. While the well-known flattening of the radio number counts below 1 mJy is mostly due to star-forming galaxies, these sources and AGN make up an approximately equal fraction of the sub-mJy sky. Our results imply that radio emission from z ~ 2 radio-quiet AGN is closely related to star formation. Finally, the implications of our results for future, deeper radio surveys, including those with the SKA, will also be discussed.
An important goal that has driven the development of LOFAR since its inception is to explore the low frequency radio sky through several surveys. The main science driving the design of these surveys was to use the unique aspects of LOFAR to advance our understanding of the formation and evolution of galaxies, AGNs and galaxy clusters. In this presentation we will review the LOFAR facility, discuss the current state of the analysis techniques and present several new science results from the deepest low-frequency images ever produced.
Recent models of joint evolution of super-massive black holes (SMBHs) and their host galaxies predict the presence of a key phase where accretion, traced by obscured Active Galactic Nuclei (AGN) emission, is likely coupled with powerful star formation. At the end of this phase, feedback processes likely play a major role in self-regulating the SMBH growth and in quenching the star-formation activity. AGN in this important evolutionary phase have been revealed in the last decade via surveys at different wavelengths. On the one hand, moderate-to-deep X-ray surveys have allowed a systematic search for heavily obscured AGN, whose main X-ray signature is the presence of a strong iron emission line over a flat X-ray continuum. The ultra-deep exposures in the Chandra Deep Field South carried out by Chandra (4Ms) and XMM-Newton (3Ms) have pursued this investigation up to very high redshifts (z~4). On the other hand, infrared surveys have been invaluable in offering complementary methods to select obscured AGN either via spectroscopy or photometry also in cases where the nuclear X-ray emission below 10 keV is totally obscured. In this review I will present the state of the art in the field of obscured accretion from AGN surveys, and I will highlight what is currently missing in our understanding of the key phases of AGN/galaxy co-evolution.
Compton thick AGN, those central engines hidden by large columns of gas and dust, can be elusive, lacking many of the typical strong signatures of AGN. They are important, however, especially in the context of the cosmic X-ray background and for complete accounts of black hole growth in galaxies. How are Compton thick AGN detected? How many of them are here (locally)? How many of them are there (at higher redshift)? Can we use indirect indicators to find them? What, if anything, do they have to do with star formation?
The extragalactic very high energy (VHE) gamma-ray sky is dominated at the moment by more than fifty blazars detected by the present imaging air Cherenkov telescopes (IACT), with a majority (about 90%) of high-frequency peaked BL Lac objects (HBL) and a small number of low-frequency peaked and intermediate BL Lac objects (LBL and IBL) and flat spectrum radio quasars (FSRQ). A significant variability is often observed, with time scales from a few minutes to months and years. The spectral energy distribution (SED) of these blazars typically shows two bumps from the radio to the TeV range, which can usually be described by leptonic or hadronic processes. While elementary bricks of the VHE emission scenarios seem now reasonably well identified, a global picture of these sources, describing the geometry and dynamics of the VHE zone, is not yet available. Multiwavelength monitoring and global alert network will be important to better constrain the picture, especially with the perspective of CTA, a major project of the next generation in ground-based gamma-ray astronomy.
X-ray surveys provide us with one of the least biased samples of Active Galactic Nuclei (AGNs) against obscuration. Here we present the most up-to-date AGN X-ray luminosity function (XLF) and absorption function over the redshift range from 0 to 5, utilizing a large combined sample obtained from surveys performed with ROSAT, Swift/BAT, MAXI, ASCA, XMM-Newton, and Chandra. The sample, including that of the Subaru-XMM Newton Deep Survey, consists of >3700 detections in the soft (0.5-2 keV) and/or hard (>2 keV) band. We utilize a maximum likelihood method to reproduce the count-rate versus redshift distribution for each survey, by taking into account the evolution of the absorbed fraction, the contribution from Compton-thick AGNs, and AGN broad band X-ray spectra including reflection components from tori based on the luminosity and redshift dependent unified scheme. We find that the shape of the XLF at z ~ 1-3 is significantly different from that in the local universe, for which the luminosity dependent density evolution (LDDE) model gives better description than the luminosity and density evolution (LADE) model. These results establish the standard population synthesis model of the X-Ray Background (XRB), which well reproduces the source counts in both soft and hard bands, the observed fractions of Compton-thick AGNs, and the spectrum of the hard XRB. We present constraints on the intrinsic fraction of Compton-thick AGNs to reproduce the XRB intensity at 20--30 keV within current uncertainties. Finally, the growth history of supermassive black holes is discussed on the basis of the AGN bolometric luminosity function constructed from the new XLF.
The development of new AGNs selection techniques based on the massive multi-wavelength datasets that are becoming more and more frequent in astronomy is a crucial task to gather statistically significant samples and shed light on the physical nature of this diverse class of extragalactic sources. Novel characterizations of specific classes of sources from unexplored region of their spectrum and unusual combinations of the observational parameters can translate into new classification criteria. In this innovative data environment, the whole process ranging from the discovery of new patterns to the application of such patters to the selection of new AGNs, has to be tackled using a Knowledge Discovery (KD) workflow. A KD workflows is a combination of different KD methods that automatically extract the more interesting patters from data, reduce the complexity of the dataset and provide astronomers with the simplest possible amount of information to be interpreted. In this talk, I will describe an original KD workflow which, in one of its first applications, has led to the discovery of a previously unknown peculiar pattern followed by blazars in the mid-Infrared color space (the blazars WISE locus), and the development of a new classification criterion based on this pattern and useful to tackle different problems. The comprehensive KD workflow used to derive these results encompasses unsupervised methods for the exploration of the multi-dimensional observable spaces, and supervised method for the training and optimization of classifiers based on the patterns determined in the observable spaces. In particular, I will describe the new methods for the association of unidentified gamma-ray sources and the extraction of candidate blazars from mid-Infrared photometric catalog based on the WISE blazars locus.
A new generation of synoptic sky surveys that cover large areas of the sky repeatedly have opened a new exploration and discovery space for the time-domain astronomy. I will describe one such survey, CRTS, to illustrate both the scientific potential and the challenges in this arena, with a special focus on the time domain studies of AGN. Such surveys effectively monitor in a semi-stochastic manner millions of AGN over most of the sky, and are thus complementary to the traditional targeted monitoring studies of more modest samples of AGN. They enable novel, systematic approaches to the characterization of AGN variability, and its possible correlations with other physical properties. This includes purely variability-based methods for AGN discovery, by mining the parameter spaces defined by a set of statistical descriptors of light curves, as well as hybrid parameter spaces that also include descriptors of spectral energy distributions. Such analysis can lead to more complete, less biased samples of AGN, and provide new constraints for the physical mechanisms of AGN emission, and their evolution.
The dichotomy of jet dominated versus accretion disk dominated AGNs or "radio-loud" vs "radio-quiet" quasars can be investigated by a simultaneous determination of the relative shape and evolution of the radio and optical luminosity functions, and the distribution of the radio loudness R defined as the ratio of radio to optical luminosities. This can be done from a multivariate data set containing observed fluxes, redshift, spectra, etc. We emphasize that when dealing with a multivariate data set it is imperative to first determine the true correlations, not those introduced by the observational selection effects, among the variables (e.g. Luminosity-luminosity, redshift-luminosity) before obtaining the individual distributions of the variables (e.g. Luminosity functions and density evolution). We use data from several sources including the SDSS (Data Release 7) and FIRST radio catalogs, with well defined optical and radio flux limits, and employ the non-parametric methods developed by Efron and Petrosian, designed to obtain unbiased correlations, distributions and evolution with redshift from data truncated due to observational biases. We determine the density and the luminosity evolutions in both wavebands, which shows significantly higher radio than optical luminosity evolution. From these we obtain true distribution of the radio loudness parameter which shows no sign of bi-modality and indicates that quasars were more radio loud at earlier epochs.
I will review: 1) the current mapping of large scale cosmic structure in the COSMOS survey field, 2) the status of the on-going CXO survey (PI: Civano), 3) probing AGN with ALMA.
Various observational techniques have been used to survey galaxies and AGN, from X-rays to radio frequencies, both photometric and spectroscopic. I will review these techniques aimed at the study of galaxy evolution and of the role of AGNs and star formation as the two main energy production mechanisms. I will then present as a new observational approach the far-IR spectroscopic surveys that could be done with planned astronomical facilities of the next future.
I will discuss multi-wavelength AGN studies, with a focus on mid-IR and radio selected obscured AGN. Obscured AGN, which are robustly identified across the full sky by WISE, are the dominant AGN population. I will discuss several aspects of the mid-IR obscured AGN population, ranging from detailed studies of extreme sources, the so-called WISE ultraluminous 'hot dust-obscured galaxy' or 'hot DOG' sample, as well as more general studies comparing obscured and unobscured AGN identified in wide-area surveys.
In order to fully understand galaxy formation we need to know when in the cosmic history are supermassive black holes (SMBHs) growing more intensively, in what type of galaxies this growth is happening and what fraction of these sources are invisible at most wavelengths due to obscuration. Active Galactic Nuclei (AGN) population synthesis models that can explain the spectral shape and intensity of the cosmic X-ray background (CXRB) indicate that most of the SMBH growth occurs in moderate-luminosity (Lx~1044 erg/s) sources (Seyfert-type AGN), at z~0.5-1 and in heavily obscured but Compton-thin, NH~1023 cm-2, systems. However, this is not the complete history, as a large fraction of black hole growth does not emit significantly in X-rays either due to obscuration, intrinsic low luminosities or large distances. Taking advantage of the rich multi-wavelength data available in the Chandra Deep Field South (CDF-S), including the 4 Msec Chandra observations (the deepest X-ray data to date), in order to measure the amount of black hole accretion as a function of cosmic history, from z~0 to z~6. We obtain stacked rest-frame X-ray spectra for samples of galaxies binned in terms of their IR luminosity, stellar mass and other galaxy properties. We find that the AGN fraction and their typical luminosities, and thus black hole accretion rates, increase with IR luminosity. The integrated intensity at high energies indicates that a significant fraction of the total black hole growth, 22%, occurs in heavily-obscured systems that are not individually detected in even the deepest X-ray observations. We further investigate the AGN triggering mechanism as a function of bolometric luminosity, finding evidence for a strong connection between significant black hole growth events and major galaxy mergers from z~0 to z~3, while less spectacular but longer accretion episodes are most likely due to other (stochastic) processes. AGN activity triggered by major galaxies is responsible for ~60% of the total black hole growth.
Integral field spectroscopy provides us with immensely rich datasets about spatially resolved distributions and kinematics of emission and absorption lines. In this contribution I will describe some of the key insights that have been made about AGN using optical, near infrared, and far infrared IFUs. These encompass gas inflow and outflow mechanisms, and the relations between star formation, the torus, and accretion onto the black hole. Progress so far has largely relied on archetypal and small sets of objects. In the future, a more statistically robust approach will be required. I will end by discussing a number of issues that can easily confuse an emerging picture, and need to be borne in mind for such surveys.
I will review recent progress in understanding the connection between the growth of galaxies and the super-massive black holes at their centres, focusing mostly on the distant Universe. I will (1) discuss the connection between star formation and AGN activity, (2) review evidence that AGNs suppress star formation in their host galaxies, and (3) explore the presence, ubiquity, and potential impact of large-scale energetic outflows in AGNs on the evolution of galaxies.
There has been considerable theoretical support in recent years for the idea of quenching star formation in massive galaxies via AGN-driven winds, but relatively little direct observational evidence for it, until now. I will summarize the results of recent surveys which have revealed powerful ionized, neutral, and/or molecular galaxy-scale outflows in a number of systems. I will discuss the properties of these outflows in some detail, quantifying the role of the AGN/quasar in driving these winds, and give a critical review of the role of AGN/quasar feedback on galaxy evolution.
It is well known that some percentage of Active Galaxies with strong emission lines show double or multiple nuclei sometimes associated with jets. The sizes of these features are a few hundred parsecs and even kiloparsecs. The physical nature of these structures is not well understood. One prominent hypothesis is that they are the manifestation of colliding and merging galaxies. Another hypothesis is just some violent activity taking place in the nuclei of galaxies causing major disruptions, though at present no explanation exists for the origin of such activity. We discuss spectroscopic observations of such galaxies made with the Palomar 5m telescope, the Byurakan 2.6m telescope and the 6m telescope of the Special Astrophysical Observatory in Russia. We conclude that the major explanation of the nature of the double or multiple nuclei is not yet clear. Further study is needed.
I will argue that observations of the diffuse gas in the outskirts of quasar host galaxies, or the so called circumgalactic medium, are essential for understanding how luminous quasars evolve in a cosmological context. Such observations also provide a fruitful comparison to theory, because hydrodynamics at moderate overdensities is much easier to simulate than the complicated processes which trigger quasar activity. A novel technique will be introduced, whereby a foreground quasar can be studied in absorption against a background quasar, resolving scales as small as 30kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of diffuse gas around quasars. Hydrodynamical simulations of the massive dark matter halos which host luminous quasars under predict the amount of cool gas observed in quasar environs by a large factor, challenging our understanding of how massive galaxies form. I will also discuss a very sensitive search for Ly-alpha emission from the same gas which we study in absorption.
The Great Observatories All-sky LIRG Survey (GOALS) is combining imaging and spectroscopic data from the Herschel, Spitzer, Hubble, GALEX, Chandra, and XMM-Newton space telescopes augmented with extensive ground-based observations in a multiwavelength study of approximately 180 Luminous Infrared Galaxies (LIRGs) and 20 Ultraluminous Infrared Galaxies (ULIRGs) that comprise a statistically complete subset of the 60um-selected IRAS Revised Bright Galaxy Sample. The objects span the full range of galaxy environments (giant isolated spirals, wide and close pairs, minor and major mergers, merger remnants) and nuclear activity types (Seyfert 1, Seyfert 2, LINER, starburst/HII), with proportions that depend strongly on the total infrared luminosity. I will review the science motivations and present highlights of recent results selected from over 25 peer-reviewed journal articles published recently by the GOALS Team. Statistical investigations include detection of high-ionization Fe K emission indicative of deeply embedded AGN, comparison of UV and far-IR properties, investigations of the fraction of extended emission as a function of wavelength derived from mid-IR spectroscopy, mid-IR spectral diagnostics and spectral energy distributions revealing the relative contributions of AGN and starbursts to powering the bolometric luminosity, and quantitative structure analyses that delineate the evolution of stellar bars and nuclear stellar cusps during the merger process. Multiwavelength dissections of individual systems have unveiled large populations of young star clusters and heavily obscured AGN in early-stage (II Zw 96), intermediate-stage (Mrk 266, Mrk 273), and late-stage (NGC 2623, IC 883) mergers. A recently published study that matches numerical simulations to the observed morphology and gas kinematics in mergers has placed four systems on a timeline spanning 175-260 million years after their first passages, and modeling of additional (U)LIRGs is underway. A very brief description of ongoing work with Herschel and ALMA will be given. The talk will conclude with a discussion of the demographics of dual AGN (kpc-scale orbits) in the GOALS sample, including the difficulty of their detection and confirmation, a proposed sequence representing a progression from dual AGN to binary AGNs (sub-pc scale orbits), and implications for the scarcity of confirmed binary QSOs in recent large surveys. Grant support from NASA is gratefully acknowledged.
Variability is a successful technique used to identify AGN in both ground and space-based galaxy surveys. Optical variability surveys using HST have uncovered a number of AGN in deep extragalactic fields extending to z~3 and probing intrinsically faint galaxies. Mid-IR variability surveys using Spitzer observations have identified a significant numbers of AGN and are particularly sensitive to obscured sources. Many variability detected AGN are not strong X-ray sources or lack the characteristic mid-IR colors of AGN and would thus be unidentified using other selection techniques. I will discuss the nature of the variable sources and their host galaxies from both optical and mid-IR surveys.
The Evolutionary Map of the Universe (EMU) is a large radio continuum survey to be undertaken on the Australian SKA Pathfinder (ASKAP) telescope, under construction in Australia. EMU will detect and catalog about 70 million galaxies, increasing thirty-fold the number of known radio sources. Such large numbers enable new approaches to the study of AGN evolution and their role in the evolution of their hosts, while the high sensitivity enables the study of star-forming galaxies and low-luminosity AGN even to high redshifts. The EMU catalog will include not only AGNs at the very highest redshifts, but also highly obscured AGN that are invisible at most other wavelengths, and perhaps rare and unexpected objects that will be discovered serendipitously. The challenge will be in the interpretation of these large datasets, and new approaches and algorithms will be needed to turn these data into science.
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is current scheduled for launch in Q4 2014. eROSITA will perform a deep survey of the entire X-ray sky. In the soft band (0.5-2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2-8 keV) it will provide the first ever true imaging survey of the sky. The design driving science is the detection of large samples of galaxy clusters to redshifts z > 1, in order to study the large scale structure in the Universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of around 3 million active galactic nuclei, which is bound to revolutionize our view of the evolution of supermassive black holes and their impact on the process of structure formation in the Universe. The survey will also provide new insights into a wide range of astrophysical phenomena, including isolated Neutron Stars and Black Holes, X-ray binaries, active stars and diffuse emission within the Galaxy, as well as more exotic ones such as gamma-ray bursts, tidal disruption of stars in galactic nuclei and binary black holes. In this talk I will present the main characteristics of the mission and focus on the scientific drivers for extragalactic all-sky surveys of AGN.