Event schedule

Welcome Reception

Detecting Elusive Black Holes in the JWST Era

Session: How do elusive AGNs impact our understanding of SMBH ‘seed’ models? Theoretical Perspective

The first black hole seeds likely formed when the Universe was younger than 500 Myr old and they played an important role in the growth of early (z=7) supermassive black holes. While much progress has been made in understanding their formation and growth, their observational signatures remain largely unexplored. As a result, we are yet to detect these sources. We present a novel photometric method to identify black hole seed candidates in deep multi-wavelength surveys. The method relies on infrared and X-ray observations and selects the only two objects with a robust X-ray detection found in the CANDELS/GOODS-S survey with a photometric redshift z>6. Moreover, we present the case of CR7, a Lyman alpha emitter at z=6.6 whose observational features are also compatible with our black hole seed model. To date, the se objects represent the most promising black hole seed candidates, possibly formed via the direct collapse black hole scenario. While this result is based on the best photometric observations of high-z sources available to date, additional gains are expected from deeper spectroscopic and X-ray data. For this reason, we explore the role that JWST will play in the detection of the first black holes in the Universe.

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Fabio Pacucci , Yale University

Supermassive Black Hole Seeds in Cosmological Simulations

Session: How do elusive AGNs impact our understanding of SMBH ‘seed’ models? Theoretical Perspective

Supermassive black holes are well understood to play an important role in galaxy evolution, as well as acting as an observational probe reaching back to the very early universe. One of the most uncertain aspects of supermassive black holes is the mechanism by which their initial seeds form and the efficiency and frequency with which this occurs. Using high-resolution cosmological simulations and post-processing analysis of black hole accretion and merger histories, I will discuss which observables are affected by changing the seed prescription. In particular, I will focus on how global properties such as the black hole mass function, global accretion rate density, and the quasar luminosity function depend on the fraction of halos capable of forming SMBH seeds and the types of halos in which they form (e.g. based on the metallicity and spin parameter of the halo), and the possible constraints we can determine from current and upcoming observational surveys.

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Colin DeGraf , Institute of Astronomy, University of Cambridge

Radiation-hydrodynamic Simulations of Obscured AGN: a Striking Correlation Between the Spectral Shape of Dust Thermal Emission and the Black Hole Eddington Ratio

Session: How do elusive AGNs impact our understanding of SMBH ‘seed’ models? Theoretical Perspective

Recent observations show large amounts of dust around supermassive black holes (SMBHs) in the early Universe. However, the accretion mechanism of SMBHs in dusty gas is not well understood. In this talk I will present a study of the growth of massive black holes (MBHs) in dusty clouds by using one-dimensional radiative-hydrodynamics simulations. We find that the accretion of dusty gas onto MBHs proceeds gently with small fluctuations of the accretion rate, whereas that of less dusty or pristine gas causes more violent periodic bursts. At dust-to-gas mass ratios similar to the solar neighborhood, the time averaged luminosity becomes smaller than that for primordial gas by one order of magnitude. We derive spectral energy distributions at IR bands by calculating dust thermal emission and show that the flux ratio between $\lambda < 20 \mu m$ and $> 100 \mu m$ is closely related to the Eddington ratio, independently of the BH mass, gas density, metallicity, etc. Thermal emission from hot dust near the BH dominates only during the high accretion phase producing higher flux at $~20 \mu m$, while a warm dust component located further out, although fainter during the quiescent phases of the accretion, it is always present. Testing this model observationally requires minimizing the contribution from warm dust associated with star formation using high resolution observations, some of which are already available using Hershel and Spitzer. We therefore suggest that the combination of MIR observations by JWST and FIR observation by ALMA may be used to estimate the Eddington ratio of obscured AGNs.

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Massimo Ricotti , University of Maryland

Properties of Active Galactic Nuclei in Dwarf Galaxies

Session: How do elusive AGNs impact our understanding of SMBH ‘seed’ models? Observational Perspective

Searching for signs of black hole accretion is the best way of identifying black holes in dwarf galaxies. In the last several years, the number of dwarf galaxies with known active galactic nuclei (AGN) has increased by over an order of magnitude, thanks to large scale surveys such as the Sloan Digital Sky Survey. These objects comprise a new population of AGN. As such, it is important to characterize this population to understand how they compare to AGN in more massive systems, as well as to determine which factors influence the presence of AGN in dwarf galaxies. I will discuss X-ray and ultraviolet observations of a sample of dwarf galaxies with optical signatures of AGN activity (Baldassare et al. 2017). I will also discuss new results from Hubble Space Telescope WFC3 observations of RGG 118, a dwarf galaxy hosting an actively accreting 50,000 solar mass black hole in its core.

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Vivenne Baldassare , University of Michigan

Hard X-Ray-selected AGNs in Low-mass Galaxies

Session: How do elusive AGNs impact our understanding of SMBH ‘seed’ models? Observational Perspective

I will present properties of the sample of low-mass AGNs selected from the ∼13 deg2 NuSTAR Serendipitous Survey. This z<0.3 sample of 10 low-mass AGN has median r-band absolute magnitude and 2-10 keV luminosity comparable to those of broad-line IMBH host galaxies selected from large optical spectroscopic surveys. One of the 10 galaxies in our sample, J115851+4243.2, shows evidence for heavy X-ray absorption and 30 (+16,- 9)% of our sample do not show AGN-like emission lines in their optical spectra, implying that a fraction of the low-mass AGNs might be missed by spectroscopic surveys in the optical wavelengths. The mid-IR colors of our sample also indicate that these optically normal low-mass AGNs cannot be efficiently identified with typical AGN selection criteria based on Wide Field Infrared Survey Explorer colors. While the hard X-ray-selected low-mass AGN sample size is still limited, our results show that sensitive NuSTAR observations are capable of probing faint hard (> 10 keV) X-ray emission originating from the nuclei of low-mass galaxies out to moderate redshift (z< 0.3), thus providing a critical step in understanding AGN demographics in low-mass galaxies. I will also present the results from the XSERVS-LSS survey, which is a deep XMM-Newton survey targeting the central 4 deg^2 of the XMM-LSS field.

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Chien-Ting Chen , Pennsylvania State University

The (Elusive) Fossil Record of Black Hole Seeds

Session: How do elusive AGNs impact our understanding of SMBH ‘seed’ models? Observational Perspective

In principle, the black hole content of low-mass galaxies is a "fossil record" of black hole seed formation in the early Universe. But in practice, a black hole census in low-mass galaxies has remained elusive due to selection biases in standard AGN selection techniques. I will demonstrate and quantify how star formation "dilutes" and hides significant black hole growth in low-mass galaxies, along with an estimate of black hole content among SDSS galaxies after correcting for this bias. Spatially resolved spectroscopy greatly increases the efficiency of AGN selection by mitigating the dilution from extended star formation emission. I will show the current constraints on bimodal black hole seed formation from HST grism spectroscopy, and will also anticipate some of the observations we can expect from similar JWST and WFIRST grism spectra.

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Jonathan Trump , University of Conneticut

Intermediate Mass Black Holes Manifested as Low-Luminosity Active Galactic Nuclei

Session: How do elusive AGNs impact our understanding of SMBH ‘seed’ models? Observational Perspective

Intermediate mass black holes (IMBHs) with masses in the range of 500 to 200000 MSun represent a crucially important link between the populations of stellar mass black holes and supermassive black holes residing in galaxy centers. We have identified several low luminosity nearby active galactic nuclei in the SDSS legacy galaxy sample having X-ray counterparts and estimated their virial masses to be between 30000 and 200000 MSun. IMBH hosts are expected to have had poor merger histories without major mergers in the past and, therefore, might represent the relics of pristine galaxy population survived through the cosmic time almost intact. Here we present preliminary stellar population analysis of IMBH hosts made from their SDSS spectra. We seek answers to the following questions: (i) why didn't IMBHs grow? (ii) how do IMBHs affect their host galaxies? (iii) how did IMBH hosts evolve through the cosmic time? We plan to follow-up several IMBH hosts with the JWST NIRspec IFU and obtain: (i) spatially resolved star formation histories; (ii) maps of stellar and gas kinematics; (iii) maps of NIR emission line ratios in the narrow-line AGN region; (iv) improved IMBH mass estimates using AGN broad line region in H-alpha and Paschen-alpha.

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Ivan Katkov , Sternberg Astronomical Institute, Moscow State University

Uncovering the Full Population of Elusive Growing Black Holes with X-ray and Multiwavelength Surveys

Session: What fraction of SMBH growth is currently being missed and what impact does this have?

Despite remarkable recent progress, our picture of black hole evolution has remained incomplete due to the challenges of detecting the elusive AGN that are highly obscured or hidden beneath the light of their host galaxies. It is now clear that AGN obscuration can be linked to processes in galaxy evolution, and that black hole growth is highly stochastic and variable, so that studying these weak or obscured AGN is essential to understanding the big picture of black hole evolution. I will review recent progress in uncovering the complete AGN population using deep, wide X-ray and multiwavelength surveys along with the next generation of black hole and galaxy evolution models. I will then point to the potential for the future with the next generation of extragalactic surveys, and forecast the exciting science that will be enabled by the Lynx concept X-ray mission.

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Ryan Hickox , Dartmouth College

A Universal Model for the AGN Phenomenon

Session: What fraction of SMBH growth is currently being missed and what impact does this have?

I present ongoing work on building a universal model for the AGN phenomenon. We forward model the luminosity and variability of AGN as they grow together with the galaxy population to give rise to the diverse phenomenology of Seyferts, quasars and radio galaxies. Using this forward modeling approach, we can constrain the physics driving black hole growth and the role black hole growth phases have in the evolution of galaxies. We find that the AGN phenomenon is largely insensitive to the particular features of their host galaxies, and is rather driven by physics near the AGN central engine, or even in the accretion disk itself. The only difference is the activity in blue and red galaxies, with some modification in the case of major mergers. I make the case that a full understanding of the AGN phenomenon requires consideration of the variability spectrum on all time scales, from seconds to the age of the universe.

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Kevin Schawinski , ETH Zurich

Hiding in Plain Sight: AGN Echoes of Low-Redshift Lyman Alpha Blobs

Session: What fraction of SMBH growth is currently being missed and what impact does this have?

We have discovered extremely luminous optical nebulae whose ionization states are characteristic of active galactic nuclei (AGN), yet lack signatures of current powerful activity, such as X-ray emission. We identify these emission sources as ionization echoes of past activity, where the AGN have faded by three to four orders of magnitude in the last 10,000 to 100,000 years. They remain bright at mid-infrared (MIR) wavelengths, so offsets from standard X-ray–MIR relationships do not necessarily imply AGN obscuration. The properties of this group are related to the duty cycle of AGN and the time lag for dust reprocessing of the central emission. We use near-ultraviolet observations to demonstrate that these powerful galaxies, having Lyman alpha luminosities on the order of 10^43 erg/s, are low-redshift (z ~ 0.3) counterparts of “Lyman alpha blobs” (LABs). LABs were more common at z > 2 and are sites of massive galaxy formation. Most of the low-redshift hosts are interacting or merging galaxies, located in more isolated environments rather than in the massive structures that high-redshift LABs prefer. Although rare, the relatively nearby counterparts offer opportunities to measure physical conditions and processes including the escape of Lyman alpha photons, and most importantly, to determine their underlying sources of ionization and luminosity.

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Nancy Levenson , Space Telescope Science Institute

Characterizing Black Hole Growth Across the Galaxy Population Using Deep X-ray Data

Session: What fraction of SMBH growth is currently being missed and what impact does this have?

Deep X-ray observations are uniquely capable of identifying growing supermassive black hole accretion down to very low levels of accretion within various galaxy types that may be missed with other diagnostics, thus providing vital insights into the elusive population of AGN. I will present new measurements that push the limits of the deepest Chandra X-ray surveys to accurately characterize the distribution of black hole accretion rates within large samples of star-forming and quiescent galaxies spanning out to z~4. Our results reveal a broad distribution of accretion rates in both galaxy types, reflecting long-term variability in the level of AGN fuelling. We also find that the incidence of AGN in star-forming galaxies is higher than in quiescent galaxies and undergoes a strong, stellar-mass-dependent evolution. The probability of a quiescent galaxy hosting an AGN is generally lower and evolves differently with redshift. These results provide new insights into the physical mechanisms that drive the growth of supermassive black holes across the galaxy population and the potential impact of AGN on the different stages of galaxy evolution.

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James Aird , University of Cambridge'

Obscuration/orientation Effects in the Chandra Observed Sample of Medium-Redshift (0.5 < z < 1) 3CRR Sources

Session: What fraction of SMBH growth is currently being missed and what impact does this have?

The level of accretion power in the Universe has fundamental implications both for cosmology and the physics of active galactic nuclei (AGN). Despite their intrinsically bright, multi-wavelength emission, an unknown AGN fraction remain under cover, their nuclei invisible due to orientation-dependent obscuration by massive amounts of material. One way to select AGN samples that are orientation-unbiased (although limited to radio-loud sources) is low frequency radio, where the selection is based on extended radio lobes. The radio data also provide an independent estimate of orientation via the radio core fraction. We extend our studies of a complete, low-frequency (178 MHz) radio selected, Chandra observed sample of high-redshift (1 21) and edge-on inclinations. These properties together with the observed trend of increasing NH with decreasing radio core fraction are roughly consistent with orientation-dependent obscuration as in Unification models. However, four NLRGs show low NH (log NH ~ 21-22), high quasar-like Lx/Lradio ratios, soft hardness ratios, and weak near-to-mid-IR emission which require an extremely thin and cool torus or obscuration by the host galaxy. The ratio of unobscured to Compton-thin to Compton-thick sources is: 5.5:4.5:1 (high-z sample: 2.5:1.4:1), where 11% of sources are Compton-thick (compared to 25% at high-z).

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Joanna Kuraszkiewicz , Smithsonian Astrophysical Observatory

Is Black Hole Growth a Universal Process? Exploring Selection Effects in Measurements of Eddington Ratios and Host Galaxies of AGN

Session: What physical properties influence AGN detectability and what are the best techniques to find them?

Our understanding of the connection between AGN and their host galaxies and the underlying properties of the full AGN population is presently limited by complex observational biases that are difficult to untangle using conventional methods and theoretical models. Determining the Eddington ratio distribution in the optical, in particular, can be strongly influenced by selection effects and dilution from host galaxy star formation. Using spectroscopic galaxies from SDSS, we show that an optically selected AGN population is consistent with being drawn from an AGN Eddington ratio distribution in the form of the broad Schechter function when these selection effects are taken into account. A broad distribution is likewise observed in the X-rays to describe AGN accretion. To more completely explore selection effects, we use a semi-numerical galaxy formation simulation along with this universal Eddington ratio distribution to describe the multi-wavelength AGN population. With this model, we can probe the more elusive AGN that are not selected using conventional techniques. In particular, we explicitly model selection effects to produce the “observed” AGN population for comparison with both theoretical and observational X-ray data. We investigate the impact on the “observed” population of selecting AGN in the X-rays based on a thresholds in luminosity (as they are selected in most surveys). We find that we can broadly reproduce the host galaxies and halos of the X-ray AGN population, and that different AGN selection techniques yield samples with very different host galaxy properties.

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Mackenzie Jones , Dartmouth College

Dependence of Optical AGN Identification on Stellar Population Models and Spectral Quality

Session: What physical properties influence AGN detectability and what are the best techniques to find them?

Optical emission lines provide a clear signature for the presence of an AGN. However, in order to to have a reliable measurement of the optical line ratios used in Type 2 AGN identification, the host galaxy contribution must be accurately determined. In a systematic study of empirical, theoretical, and mixed stellar populations models, using SDSS spectra, we find significant discrepancies in line ratios when using different stellar templates, with a larger impact on low luminosity AGNs. We also find that the detected AGN fraction depends on the signal-to-noise ratio of the spectra used. We quantify these effects on our all-sky, near-by, optical AGN catalog, uniformly selected from the parent sample of galaxies in the 2MASS Redshift Survey and cross correlate our catalog with all-sky AGN catalogs at other wavelengths to assess their impact on finding a complete sample of AGNs.

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Ingyin Zaw , New York University Abu Dhabi

Unveiling the Elusive AGNs in Millions of SDSS and WISE Galaxies

Session: What physical properties influence AGN detectability and what are the best techniques to find them?

The advent of the Wide-field Infrared Survey Explorer (WISE) has given us the opportunity to study the complete obscured AGN population with a large-area multi-wavelength approach. We present the results of SDSS+WISE spectral energy distributions (SEDs) of over one million galaxies with optical detection and a single mid-IR color cut of W2-W3 > 2.0 to remove contamination from stars. We model our SEDs using a set of empirically derived stellar and AGN templates to derive the AGN luminosity and nuclear obscuration for the full detected galaxy population in our sample. By modeling all available galaxies we are unconstrained by selection biases inherent with any given color selection criterion, and instead opt to determine the characteristics of the broader obscured AGN population given the results of our models. The luminosities and WISE infrared colors are used to determine the underlying complete population of obscured AGN, including those that would go undetected and unselected with various selection criteria. We further explore the low- and high-redshift objects in our sample for difference in their photometry and rest-frame colors.

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Christopher Carroll , Dartmouth College

The Elusive Nature of the AGN in NGC 1266

Session: What physical properties influence AGN detectability and what are the best techniques to find them?

The role of AGN in the transition of galaxies from actively star forming to quiescence is still not fully understood, and is particularly challenging to study for AGN that are weak or hidden by obscuration or host dilution. NGC 1266 is a transitioning galaxy, home to massive molecular outflow driven by its AGN. The turbulence injected into its interstellar medium by the outflow, indicated by its shocked optical gas ratios, may account for the suppression of its star formation activity by a factor of at least 50. While the AGN clearly has an important mechanical impact on NGC 1266, its radiative qualities are more difficult to characterize. ALMA and CARMA measurements of dense gas tracers show that its nuclear region lies behind a column of N(H2) = 3 x 10^24 cm^-2. Continuum ALMA observations barely resolve a region of FIR emission within 30pc of the nucleus emitting L(IR) > 10^10 LSun, which could be heated either by a luminous AGN or an ultracompact nuclear starburst. We use a new deep Chandra observation combined with a NuSTAR observation of NGC 1266 to determine the radiative properties of its AGN and thereby its contribution to the dust heating observed by ALMA with implications on the distribution of the star formation suppression.

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Lauranne Lanz , Dartmouth College

The Complete IR View of Swift/BAT 70 Month AGN Catalog

Session: What physical properties influence AGN detectability and what are the best techniques to find them?

We systematically investigate the near- to far-infrared (FIR) photometric properties of a nearly complete sample of local active galactic nuclei (AGN) detected in the Swift/BAT all-sky ultra-hard X-ray (14-195 keV) survey. Out of 606 non-blazar AGN in the Swift/BAT 70 month catalog at high galactic latitudes of |b| > 10^degree , we obtain IR photometric data of 604 objects by cross-matching the AGN positions with catalogs from the WISE, AKARI, IRAS, and Herschel infrared observatories. We find a good correlation between the ultra-hard X-ray and mid-IR luminosities over five orders of magnitude (41 View Slides

Kohei Ichikawa , Columbia University / NAOJ

Obscured and Reddened Quasars at the Peak of Galaxy Formation

Session: Elusive AGNs at high redshift? / Prospects for Future Facilities

While classification of large samples of obscured and reddened quasars at the peak of quasar activity and black hole growth (z~2.5) remains challenging, their identification is imperative to advance our understand of galaxy evolution. This is the case because obscured and reddened quasars may represent not just a specific quasar orientation but instead a unique stage of quasar evolution that mediates the relationship between black hole activity and galaxy evolution. Our group has developed several observational techniques to identify obscured and highly reddened quasars at z~2.5 using a combination of the SDSS spectroscopy and WISE photometry. Our sample contains objects with some of the most extreme ionized gas velocities observed (> 5000 km/s), indicating wind speeds too large to be contained by the galaxy potential though they are radio quiet. The most extreme of these objects may thus represent the “blowout phase” of AGN evolution that precedes or accompanies the cessation of star formation in the host galaxy due to the effects of radiatively-driven quasar winds. I will present both our sample selection and results from multi-wavelength follow-up of this sample to search for the presence of multi-scale quasar winds. In particular, Keck spectropolarimetry reveals high levels of polarized light (reaching ~20% of the total continuum emission in some cases) and changes in the polarization fraction and position angle across emission lines that argues for the presence of dusty outflows on scales of the emission line region. I will also present new efforts using the VLA to study the molecular gas content of the galaxy using CO (1-0) to search for the presence of galaxy-scale winds launched by the quasar and capable of clearing the galaxy of molecular gas.

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Rachael Alexandroff , Johns Hopkins University

Obscured Quasars in the Cosmic Web: Dark Matter Halos and Unification Models

Session: Elusive AGNs at high redshift? / Prospects for Future Facilities

Recent work has identified an important difference in the dark matter halo masses of IR-selected obscured and unobscured quasars, suggesting that these classes cannot be fully unified using orientation alone. However, the difference has not been strong, casting doubt on its significance. We expand the footprint of angular clustering and CMB lensing cross-correlations to the full SDSS footprint to improve the precision of previous measurements, correcting for position-dependent biases introduced in the larger area. In doing so, and by combining independent halo mass measurements, we confirm obscured quasars reside in halos a factor of 3 more massive than their unobscured counterparts at a significance of 5-sigma. We also utilize cross-correlations and analysis of 12 and 22 micron WISE data to confirm that the redshifts and luminosities of these populations are well-matched and allow for fair comparisons. Additional confirmation of the halo mass difference is found from cross-correlations with spectroscopic quasars. Finally, we provide a simple evolutionary model from obscured to unobscured quasar that, when combined with a luminosity cut, can explain these observed mass differences. It is increasingly likely that both orientation and evolution, and possibly additional factors, are required to fully understand luminous obscured quasars.

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Mike DiPompeo , Dartmouth College

The High-Redshift (z>3) AGN Population in the Deepest Chandra Fields

Session: Elusive AGNs at high redshift? / Prospects for Future Facilities

Deep X-ray surveys provide unprecedented access to the population of accreting supermassive black holes (SMBH) at high redshift. We will present our recent results on the 33 AGN. In particular, we derived a large fraction (50-80%) of heavily-obscured (logNH>23) AGN, which does not evolve significantly from z=3 to 6 but show a positive dependence on luminosity. Although this was already suggested by previous works, thanks to the use of the deepest X-ray data available we could investigate this behavior down to logL~42. We also found that the mass growth of SMBH at high-redshift is dominated by the fast and short AGN phase, with a possible low-rate, continuous accretion in galaxies playing a secondary role. Finally, we will show our findings on the high-redshift AGN X-ray luminosity function, focussing in particular on the slope of the faint end, accessible only by the deepest X-ray surveys. This is particularly important to assess the contribution of AGN to the cosmic reionization. All of these results will be placed in the context of SMBH seeds formation and growth, and comparison with expectations from simulations will be provided. We will also discuss how future missions like Lynx, Athena and JWST will boost our knowledge of the SMBH formation and evolution in the early universe.

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Fabio Vito , Penn State University

The Deepest Radio View of AGN in the COSMOS Field: a Two-fold Population

Session: Elusive AGNs at high redshift? / Prospects for Future Facilities

I will present the latest results obtained from the 3 GHz VLA-COSMOS Large Project, the deepest radio survey ever conducted over the COSMOS field (2.6 sq.deg.). We collected nearly 11000 radio sources down to unprecedented sensitivity (2.3 uJy/beam), and identified about 3000 AGN based on X-ray, mid-infrared (MIR) and radio diagnostics. I will show how this AGN sample is an unique and ideal benchmark to track the impact of AGN feedback onto their host-galaxies across 0 View Slides

Ivan Delvecchio , University of Zagreb

Elusive Dual AGN, Revealed by WISE

Session: Elusive AGNs and the role of Mergers

Since all (massive) galaxies are thought to host central supermassive black holes, close black hole pairs should be a natural by-product in the late stages of galaxy mergers. The merging of these close black hole binaries not only represents a major avenue for black hole growth, but should also produce the loudest gravitational wave signals. Fortunately, the galaxy merger process triggers inward gas flows that lead to AGN, potentially making accreting black hole pairs ripe for detection. However, only a handful of dual AGN with separations <10 kpc have been confirmed with X-rays, despite intensive systematic searches. In this talk, I will present the results from a pilot survey for dual AGN that uses mid-IR colour selection and in a single modest observing campaign with Chandra has increased the number of X-ray confirmed dual AGN by ~50%.

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Sara Ellison , University of Victoria

Near-IR Explorations of Buried AGN in Advanced Mergers

Session: Elusive AGNs and the role of Mergers

Close separation dual AGNs provide unambiguous confirmation of ongoing mergers where the black holes experience their most rapid growth. Most of these systems have been discovered serendipitously, and confirmed cases remain, however, extremely rare. Here, we present the results of the analysis of new near-IR spectroscopy of nine advanced merger systems that display mid-IR colors suggestive of AGNs while lacking signatures of activity in the optical. We confirm the presence of broadened and/or high-excitation lines indicative of powerful AGN, reveal signs of hidden AGN feedback in the form of kinematic outflows, measure the properties of the host stellar populations, and begin to probe the gas-metallicities in these systems. Our results yield critical evidence that the epoch of peak black hole growth in mergers occurs in a highly obscured phase, consistent with theoretical predictions. This is one of the first detailed investigations into the physical environment of optically obscured dual AGNs, and provides key indications for finding and characterizing elusive black hole accretion.

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Anca Constantin , James Madison University

The Triggering of z~1 Obscured AGN in Merging Systems

Session: Elusive AGNs and the role of Mergers

Collisions and interactions between galaxies are thought to be pivotal stages in their formation and evolution, causing the rapid production of new stars, and possibly serving as a mechanism for fueling supermassive black holes (BHs). Harnessing the exquisite spatial resolution (0.3–0.7 arcsec) afforded by the Hyper Suprime-Cam (HSC) Survey, I will present our new constraints on the importance of galaxy-galaxy major mergers (1:4) in growing obscured BHs throughout the last ~7 Gyrs. Utilizing mid-infrared observations in the WISE All-Sky survey, we have robustly selected obscured AGN, starburst, and mass-matched control galaxy samples, totaling >150,000 spectroscopically confirmed systems at i<22 mag. Using our novel machine-learning technique, we identify galaxy interactions and use these data to map the growth of BHs as a function of interaction-stage, redshift and AGN luminosity, ultimately providing the necessary large-number statistics required to investigate merger-AGN triggering in the context of galaxy evolution out to z~1. Our large sample of late-merger-stage AGN will serve as an unbiased foundation for follow-up with upcoming sensitive and high-resolution instruments, such as the James Webb Space Telescope.

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Andy Goulding , Princeton University

Near-infrared Spectroscopy of Nearby Hard X-ray Selected AGN

Session: Finding Elusive AGNs: Infrared and Millimeter Studies

Since the near-infrared (NIR) part of the spectrum is nearly ten times less obscured than the optical, NIR spectroscopy of active galactic nuclei (AGN) can potentially detect emission line regions that are hidden at other wavelengths, especially in obscured AGN. For instance, NIR coronal lines, by virtue of their high ionization potential, may be more effective in detecting heavily obscured AGN than classical optical diagnostic methods. Additionally, it may be possible to observe broad lines region in the NIR, that are not visible in the optical. In this talk, I will present my study on the NIR spectroscopic properties of a sample of 100 nearby hard X-ray selected AGN. I will present the NIR AGN emission line diagnostics and I will compare the relation between X-ray, NIR and optical emission lines properties to better understand AGN variability and obscuration. I will also discuss the possibility to apply these results to the study of AGN at z~1 using the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope.

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Isabelle Lamperti , University College London

A Near-Infrared Perspective on Disentangling AGN from Shocks and Uncovering Other Elusive AGN

Session: Finding Elusive AGNs: Infrared and Millimeter Studies

AGN and starbursts are the dominant power engines in the nuclei of infrared luminous systems, particularly in the local universe where they are often fueled by the influx of gas into the center through merger mechanisms. A powerful way to diagnose the ionizing sources is through a set of well-studied optical emission lines. However, significant contribution from shocks mimicking the line ratios for hard AGN ionization has come to light in recent years. The advanced optical tools used in these diagnostics encounter challenges at both physical and technical levels, e.g. shocks and other photoionization processes are difficult to discern using only optical lines, and that the nuclei of these merger systems are often dusty and optically thick. With high-resolution near-infrared integral-field observations taken with OSIRIS on Keck, I will demonstrate the power of near-infrared diagnostics such as H_2, Br g, and coronal lines (e.g. [Si VI]) in identifying and characterizing shocks as well as in distinguishing AGN in the obscured cases. We can employ similar techniques to reveal the presence of optically-elusive AGN. These tools and calibrations will become indispensable for understanding galaxy evolution as we enter the era of JWST and new infrared instruments on 30-meter class telescopes.

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Gabriela Canalizo , University of California Riverside

ALMA Molecular Line Observations as a Tool to Scrutinize Elusive Deeply Buried AGNs in Luminous Infrared Galaxies

Session: Finding Elusive AGNs: Infrared and Millimeter Studies

We present the results of our ALMA Cycle 0-4 observations of dusty luminous infrared galaxies (LIRGs) using dense gas tracers, HCN, HCO+, and HNC, at J=4-3 and 3-2. We aim to establish a reliable method to scrutinize elusive, deeply buried AGNs in the dusty LIRG population, based on molecular line flux ratios, at the dust-extinction-free (sub)millimeter wavelength range. We confirmed a trend that LIRGs with optically- or infrared-identified AGNs show higher HCN-to-HCO+ flux ratios at J=3-2 and J=4-3, than starburst-dominated LIRGs. Two LIRGs without infrared-identified AGNs show high observed HCN-to-HCO+ flux ratios, as seen in AGN-important galaxies, but our ALMA data suggest the presence of luminous infrared 14 micron continuum emitting energy sources (=AGNs) to vibrationally excite HCN/HNC to the v2=1f level by infrared radiative pumping. These LIRGs may contain extremely deeply buried AGNs which are still elusive in the infrared energy diagnostic methods, but first detected at the (sub)millimeter wavelength range, due to even lower dust extinction effects. An enhanced HCN abundance in molecular gas highly affected by AGN's radiation can explain the observational results, and is supported from our ALMA isotopologue molecular line observations. We also found that line-opacity-corrected intrinsic molecular line flux ratios can be an even more solid tool to unveil deeply buried AGNs in dusty LIRGs than observed ratios.

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Masatoshi Imanishi , NAOJ

Mm/submm Energy Diagnostics in the ALMA Era

Session: Finding Elusive AGNs: Infrared and Millimeter Studies

Energy diagnostics at mm/submm can be vital to probe optically missed AGNs as these wavelengths do not suffer from dust extinctions. In this talk, I will first review our recent ALMA investigations of molecular diagnostics mainly using HCN and HCO+ pure-rotational lines. We suggested that HCN abundance is indeed enhanced in AGNs as compared to starburst (SB) environments at least by a factor of a few (likely >10), which can be a discriminator of AGNs and SBs. Radiative processes (i.e., XDRs) cannot solely reproduce the required abundance enhancements in AGNs. We may instead need to require mechanical heating induced by AGN jet and/or outflows to explain the HCN abundance enhancement, after taking into account the time-dependent nature of molecular chemistry as well. Hence, our HCN-based diagnostics may selectively identify AGNs with mechanical heating (i.e., those with significant “feedback” on the surrounding molecular environments). Next, I will introduce another, possible diagnostics at mm/submm regime that utilize atomic carbon emission lines. As X-ray photons much more efficiently dissociate CO molecules to C (or even ionise to C+) than UV photons, C/CO abundance ratio can be a robust, unbiased energy diagnostics. Indeed, chemical modelings proposed drastically higher C/CO ratio in XDRs than in PDRs (by a factor of ~1000). On the other hand, single-dish based observations have not shown such drastic [CI] intensity enhancement over 13CO intensity (both are optically thin, thus reflect abundance ratios) so far. This is likely due to the limited spatial resolutions of the past observations. I will thus summarize current (observational) understanding on this C/CO ratio, and discuss our strategy for high resolution interferometric observations provided with ALMA.

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Takuma Izumi , NAOJ

June 11

Sunday

Welcome Reception

June 12

Monday

Introduction and Welcome

Opening Review

Invited Talk

Coffee Break

Detecting Elusive Black Holes in the JWST Era

Supermassive Black Hole Seeds in Cosmological Simulations

Radiation-hydrodynamic Simulations of Obscured AGN: a Striking Correlation Between the Spectral Shape of Dust Thermal Emission and the Black Hole Eddington Ratio

Lunch

Invited Talk

Properties of Active Galactic Nuclei in Dwarf Galaxies

Hard X-Ray-selected AGNs in Low-mass Galaxies

​The (Elusive) Fossil Record of Black Hole Seeds

Coffee Break

​Intermediate Mass Black Holes Manifested as Low-Luminosity Active Galactic Nuclei

​Poster Flash Talks

June 13

Tuesday

​Invited Talk

​Uncovering the Full Population of Elusive Growing Black Holes with X-ray and Multiwavelength Surveys

​A Universal Model for the AGN Phenomenon

​Coffee Break

​Hiding in Plain Sight: AGN Echoes of Low-Redshift Lyman Alpha Blobs

​Characterizing Black Hole Growth Across the Galaxy Population Using Deep X-ray Data

Obscuration/orientation Effects in the Chandra Observed Sample of Medium-Redshift (0.5 < z < 1) 3CRR Sources

​Lunch

​Invited Talk

​Is Black Hole Growth a Universal Process? Exploring Selection Effects in Measurements of Eddington Ratios and Host Galaxies of AGN

​Dependence of Optical AGN Identification on Stellar Population Models and Spectral Quality

​Coffee Break

​Unveiling the Elusive AGNs in Millions of SDSS and WISE Galaxies

​The Elusive Nature of the AGN in NGC 1266

​The Complete IR View of Swift/BAT 70 Month AGN Catalog

​Dinner

June 14

Thursday

​Invited Talk

​​Obscured and Reddened Quasars at the Peak of Galaxy Formation

​Obscured Quasars in the Cosmic Web: Dark Matter Halos and Unification Models

​Coffee Break

​Invited Talk

​The High-Redshift (z>3) AGN Population in the Deepest Chandra Fields

​The Deepest Radio View of AGN in the COSMOS Field: a Two-fold Population

​Lunch

​MBH Growth in Gas-Rich Galaxy Mergers

​Elusive Dual AGN, Revealed by WISE

​Near-IR Explorations of Buried AGN in Advanced Mergers

​Coffee Break

​The Triggering of z~1 Obscured AGN in Merging Systems

​Invited Talk

June 15

Wednesday

​Invited Talk

Near-infrared Spectroscopy of Nearby Hard X-ray Selected AGN

​A Near-Infrared Perspective on Disentangling AGN from Shocks and Uncovering Other Elusive AGN

​Coffee Break

ALMA Molecular Line Observations as a Tool to Scrutinize Elusive Deeply Buried AGNs in Luminous Infrared Galaxies

​Mm/submm Energy Diagnostics in the ALMA Era

​Coffee Break

​Conference Review

The (Elusive) Fossil Record of Black Hole Seeds

Intermediate Mass Black Holes Manifested as Low-Luminosity Active Galactic Nuclei

Poster Flash Talks

Invited Talk

Uncovering the Full Population of Elusive Growing Black Holes with X-ray and Multiwavelength Surveys

A Universal Model for the AGN Phenomenon

Coffee Break

Hiding in Plain Sight: AGN Echoes of Low-Redshift Lyman Alpha Blobs

Characterizing Black Hole Growth Across the Galaxy Population Using Deep X-ray Data

Lunch

Invited Talk

Is Black Hole Growth a Universal Process? Exploring Selection Effects in Measurements of Eddington Ratios and Host Galaxies of AGN

Dependence of Optical AGN Identification on Stellar Population Models and Spectral Quality

Coffee Break

Unveiling the Elusive AGNs in Millions of SDSS and WISE Galaxies

The Elusive Nature of the AGN in NGC 1266

The Complete IR View of Swift/BAT 70 Month AGN Catalog

Dinner

Invited Talk

Obscured and Reddened Quasars at the Peak of Galaxy Formation

Obscured Quasars in the Cosmic Web: Dark Matter Halos and Unification Models

Coffee Break

Invited Talk

The High-Redshift (z>3) AGN Population in the Deepest Chandra Fields

The Deepest Radio View of AGN in the COSMOS Field: a Two-fold Population

Lunch

MBH Growth in Gas-Rich Galaxy Mergers

Elusive Dual AGN, Revealed by WISE

Near-IR Explorations of Buried AGN in Advanced Mergers

Coffee Break

The Triggering of z~1 Obscured AGN in Merging Systems

Invited Talk

Invited Talk

A Near-Infrared Perspective on Disentangling AGN from Shocks and Uncovering Other Elusive AGN

Coffee Break

Mm/submm Energy Diagnostics in the ALMA Era

Coffee Break

Conference Review