Active Galactic Nuclei Obscuration Research Articles

Dual Role of Accretion Disk Winds as X-Ray Obscurers and UV Line Absorbers in AGN

X-ray obscuration of active galactic nuclei (AGNs) is considered in the context of ionized winds of stratified structure launched from accretion disks. We argue that a Compton-thick layer of a large-scale disk wind can obscure continuum X-rays and also lead to broad UV absorption, such as in the blue wing of C iv; the former originates from the inner wind and the latter from the outer wind, as a dual role. Motivated by a number of lines of observational evidence showing strong AGN obscuration phenomena in Seyfert 1 AGNs such as NGC 5548, we demonstrate in this work, by utilizing a physically motivated wind model coupled to post-process radiative transfer calculations, that an extended disk wind under certain physical conditions (e.g., morphology and density) could naturally cause a sufficient obscuration qualitatively consistent with UV/X-ray observations. Predicted UV/X-ray correlation is also presented as a consequence of variable spatial size of the wind in this scenario.

COSMOS2020: Investigating the AGN-obscured accretion phase at z ∼ 1 via [Ne V] selection

The black hole-and-galaxy (BH-galaxy) co-evolution paradigm predicts a phase where most of the star formation (SF) and BH accretion takes place in gas-rich environments, namely, in what are likely to be very obscured conditions. In the first phase of this growth, some of the galactic gas is funnelled toward the centre of the galaxy and is accreted into the supermassive BH, triggering active galactic nucleus (AGN) activity. The large quantity of gas and dust hides the emission and the AGN appears as an obscured (type 2) AGN. The degree of obscuration in type 2 AGNs may even reach values as high as NH > 1024 cm−2 (i.e., Compton-thick, CT). Population synthesis models of the X-ray background (XRB) suggest that a large population of CT-AGN is, in fact, needed to explain the still unresolved XRB emission at energy above 20 keV. In this work, we investigated the properties of 94 [Ne V]3426 Å-selected type 2 AGN in COSMOS at z = 0.6 − 1.2, performing optical-to-far-infrared (FIR) spectral energy distribution (SED) fitting of COSMOS2020 photometric data to estimate the AGN bolometric luminosity and stellar mass, star formation rate, age of the oldest stars, and molecular gas mass for their host-galaxy. In addition, we performed an X-ray spectral analysis of the 36 X-ray-detected sources to obtain reliable values of the AGN obscuration and intrinsic luminosity, as well as to constrain the AGN properties of the X-ray-undetected sources. We found that more than two-thirds of our sample is composed of very obscured sources (NH > 1023 cm−2), with about 20% of the sources being candidate CT-AGN and half being AGNs in a strong phase of accretion (λEdd > 0.1). We built a mass- and redshift-matched control sample and its comparison with the [Ne V] sample indicates that the latter has a higher fraction of sources within the main sequence of star-forming galaxies and shows little evidence for AGNs quenching the SF. As the two samples have similar amounts of cold gas available to fuel the SF, this difference points towards a higher efficiency in forming stars in the [Ne V]-selected sample. The comparison with the prediction from the in situ co-evolution model suggests that [Ne V] is an effective tool for selecting galaxies in the obscured growth phase of the BH-galaxy co-evolution paradigm. We find that the “quenching phase” is still to come for most of the sample and only few galaxies show evidence of quenched SF activity.

Active Galactic Nuclei Selection and Demographics: A New Age with JWST/MIRI

Understanding the coevolution of supermassive black holes and their host systems requires a comprehensive census of active galactic nuclei (AGNs) behavior across a wide range of redshift, luminosity, obscuration level, and galaxy properties. We report significant progress with JWST toward this goal from the Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES). Based on comprehensive spectral energy distribution (SED) analysis of 3273 MIRI-detected sources, we identify 217 AGN candidates over a survey area of ∼34 arcmin2, including a primary sample of 111 AGNs in normal massive galaxies (M * > 109.5 M ☉) at z ∼ 0–4, an extended sample of 86 AGN candidates in low-mass galaxies (M * < 109.5 M ☉), and a high-z sample of 20 AGN candidates at z ∼ 4–8.4. Notably, about 80% of our MIRI-selected AGN candidates are new discoveries despite the extensive pre-JWST AGN searches. Even among the massive galaxies where the previous AGN search is believed to be thorough, 34% of the MIRI AGN identifications are new, highlighting the impact of obscuration on previous selections. By combining our results with the efforts at other wavelengths, we build the most complete AGN sample to date and examine the relative performance of different selection techniques. We find the obscured AGN fraction increases from L AGN,bol ∼ 1010 L ⊙ to 1011 L ⊙ and then drops toward higher luminosity. Additionally, the obscured AGN fraction gradually increases from z ∼ 0 to z ∼ 4 with most high-z AGNs obscured. We discuss how AGN obscuration, intrinsic SED variations, galaxy contamination, survey depth, and selection techniques complicate the construction of a complete AGN sample.

Heavily obscured AGN detection: A radio versus X-ray challenge

In the supermassive black hole (SMBH)-galaxy coevolution scenario, heavily obscured active galactic nuclei (AGN) represent a fundamental phase of SMBH growth during which most of the BH mass is accreted and the scaling relations with the host galaxy are set. Obscured nuclei are thought to constitute a major fraction of the whole AGN population, but their statistics and evolution across cosmic time are still highly uncertain. Therefore, it is pivotal to identify new ways to detect this vast and hidden population of growing SMBHs. A promising way to select heavily obscured AGN is through radio emission, which is largely unaffected by obscuration and can be used as a proxy for nuclear activity. In this work, we study the AGN radio detection effectiveness in the major deep extragalactic surveys, considering different AGN obscuration levels, redshift, and AGN bolometric luminosities. We particularly focus on comparing their radio and X-ray detectability, making predictions for present and future radio surveys. We extrapolated the predictions of the AGN population synthesis model of the cosmic X-ray background (CXB) to the radio band, by deriving the 1.4 GHz luminosity functions of unobscured (i.e., with hydrogen column densities $ H &lt;22$), obscured ($22&lt; H &lt;24$), and Compton-thick (CTK, $ H &gt;24$) AGN. We then used these functions to forecast the number of detectable AGN based on the area, flux limit, and completeness of a given radio survey and compare it with the AGN number resulting from X-ray predictions. When applied to deep extragalactic fields covered both by radio and X-ray observations, we show that, while X-ray selection is generally more effective in detecting unobscured AGN, the surface density of CTK AGN radio detected is on average ten times larger than the X-ray one, and even greater at high redshifts, considering the current surveys and facilities. Our results suggest that thousands of CTK AGN are already present in current radio catalogs, but most of them escaped any detection in the corresponding X-ray observations. We also present expectations for the number of AGN to be detected by the Square Kilometer Array Observatory (SKAO) in its future deep and wide radio continuum surveys, finding that it will be able to detect more than 2000 AGN at $z&gt;6$ and tens of them at $z&gt;10$, more than half of which are expected to be CTK.

The Galaxy Activity, Torus, and Outflow Survey (GATOS)

We use JWST/MIRI MRS spectroscopy of a sample of six local obscured type 1.9/2 active galactic nuclei (AGN) to compare their nuclear mid-IR absorption bands with the level of nuclear obscuration traced by X-rays. This study is the first to use subarcsecond angular resolution data of local obscured AGN to investigate the nuclear mid-IR absorption bands with a wide wavelength coverage (4.9–28.1 μm). All the nuclei show the 9.7 μm silicate band in absorption. We compare the strength of the 9.7 and 18 μm silicate features with torus model predictions. The observed silicate features are generally well explained by clumpy and smooth torus models. We report the detection of the 6 μm dirty water ice band (i.e., a mix of water and other molecules such as CO and CO2) at subarcsecond scales (∼0.26″ at 6 μm; inner ∼50 pc) in a sample of local AGN with different levels of nuclear obscuration in the range log NHX-Ray (cm−2)∼22 − 25. We find good correlation between the 6 μm water ice optical depths and NHX-Ray. This result indicates that the water ice absorption might be a reliable tracer of the nuclear intrinsic obscuration in AGN. The weak water ice absorption in less obscured AGN (log NHX-ray (cm−2)≲23.0 cm−2) might be related to the hotter dust temperature (&gt; TsubH2O ∼ 110 K) expected to be reached in the outer layers of the torus due to their more inhomogeneous medium. Our results suggest it might be necessary to include the molecular content, such as H2O, aliphatic hydrocarbons (CH−), and more complex polycyclic aromatic hydrocarbon (PAH) molecules, in torus models to better constrain key parameters such as the torus covering factor (i.e., nuclear obscuration).

Probing the roles of orientation and multiscale gas distributions in shaping the obscuration of active galactic nuclei through cosmic time

ABSTRACT The origin of obscuration in active galactic nuclei (AGNs) is still an open debate. In particular, it is unclear what drives the relative contributions to the line-of-sight column densities from galaxy-scale and torus-linked obscuration. The latter source is expected to play a significant role in Unification Models, while the former is thought to be relevant in both Unification and Evolutionary models. In this work, we make use of a combination of cosmological semi-analytic models and semi-empirical prescriptions for the properties of galaxies and AGN, to study AGN obscuration. We consider a detailed object-by-object modelling of AGN evolution, including different AGN light curves (LCs), gas density profiles, and also AGN feedback-induced gas cavities. Irrespective of our assumptions on specific AGN LC or galaxy gas fractions, we find that, on the strict assumption of an exponential profile for the gas component, galaxy-scale obscuration alone can hardly reproduce the fraction of log (NH/cm−2) ≥ 24 sources at least at z ≲ 3. This requires an additional torus component with a thickness that decreases with luminosity to match the data. The torus should be present in all evolutionary stages of a visible AGN to be effective, although galaxy-scale gas obscuration may be sufficient to reproduce the obscured fraction with 22 &amp;lt; log (NH/cm−2) &amp;lt; 24 (Compton-thin, CTN) if we assume extremely compact gas disc components. The claimed drop of CTN fractions with increasing luminosity does not appear to be a consequence of AGN feedback, but rather of gas reservoirs becoming more compact with decreasing stellar mass.

Dust dynamics in AGN winds: a new mechanism for multiwavelength AGN variability

ABSTRACT Partial dust obscuration in active galactic nuclei (AGNs) has been proposed as a potential explanation for some cases of AGN variability. The dust–gas mixture present in AGN tori is accelerated by radiation pressure, leading to the launching of an AGN wind. Dust under these conditions has been shown to be unstable to a generic class of fast-growing resonant drag instabilities (RDIs). In this work, we present the first numerical simulations of radiation-driven outflows that explicitly include dust dynamics in conditions resembling AGN winds. We investigate the implications of RDIs on the torus morphology, AGN variability, and the ability of radiation to effectively launch a wind. We find that the RDIs rapidly develop, reaching saturation at times much shorter than the global time-scales of the outflows, resulting in the formation of filamentary structure on box-size scales with strong dust clumping and super-Alfvénic velocity dispersions. The instabilities lead to fluctuations in dust opacity and gas column density of 10–20 per cent when integrated along mock observed lines of sight to the quasar accretion disc. These fluctuations occur over year to decade time-scales and exhibit a red-noise power spectrum commonly observed for AGNs. Additionally, we find that the radiation effectively couples with the dust–gas mixture, launching highly supersonic winds that entrain 70–90 per cent of the gas, with a factor of ≲3 photon momentum loss relative to the predicted multiple-scattering momentum loading rate. Therefore, our findings suggest that RDIs play an important role in driving the clumpy nature of AGN tori and generating AGN variability consistent with observations.

X-ray properties and obscured fraction of AGN in the J1030 Chandra field

The 500ks Chandra ACIS-I observation of the field around the z = 6.31 quasar SDSS J1030+0524 is currently the fifth deepest extragalactic X-ray survey. The rich multi-band coverage of the field allowed an effective identification and redshift determination of the X-ray source counterparts; to date, a catalog of 243 extragalactic X-ray sources with either a spectroscopic or photometric redshift estimate in the range z ≈ 0 − 6 is available over an area of 355 arcmin2. Given its depth and the multi-band information, this catalog is an excellent resource to investigate X-ray spectral properties of distant active galactic nuclei (AGN) and derive the redshift evolution of their obscuration. We performed a thorough X-ray spectral analysis for each object in the sample, and measured its nuclear column density NH and intrinsic (de-absorbed) 2–10 keV rest-frame luminosity, L2 − 10. Whenever possible, we also used the presence of the Fe Kα emission line to improve the photometric redshift estimates. We measured the fractions of AGN hidden by column densities in excess of 1022 and 1023 cm−2 (f22 and f23, respectively) as a function of L2 − 10 and redshift, and corrected for selection effects to recover the intrinsic obscured fractions. At z ∼ 1.2, we found f22 ∼ 0.7 − 0.8 and f23 ∼ 0.5 − 0.6, respectively, in broad agreement with the results from other X-ray surveys. No significant variations in X-ray luminosity were found within the limited luminosity range probed by our sample (log L2 − 10 ∼ 42.8 − 44.3). When focusing on luminous AGN with log L2 − 10 ∼ 44 to maximize the sample completeness up to large cosmological distances, we did not observe any significant change in f22 or f23 over the redshift range z ∼ 0.8 − 3. Nonetheless, the obscured fractions we measure are significantly higher than is seen in the local Universe for objects of comparable intrinsic luminosity, pointing toward an increase in the average AGN obscuration toward early cosmic epochs, as also observed in other X-ray surveys. We finally compared our results with recent analytic models that ascribe the greater obscuration observed in AGN at high redshifts to the dense interstellar medium (ISM) of their hosts. When combined with literature measurements, our results favor a scenario in which the total column density of the ISM and the characteristic surface density of its individual clouds both increase toward early cosmic epochs as NH, ISM∝(1 + z)δ, with δ ∼ 3.3 − 4 and Σc, * ∝ (1 + z)2, respectively.

Resolving Galactic-scale Obscuration of X-Ray AGNs at z ≳ 1 with COSMOS-Web

A large fraction of the accreting supermassive black hole population is shrouded by copious amounts of gas and dust, particularly in the distant (z ≳ 1) universe. While much of the obscuration is attributed to a parsec-scale torus, there is a known contribution from the larger-scale host galaxy. Using JWST/NIRCam imaging from the COSMOS-Web survey, we probe the galaxy-wide dust distribution in X-ray selected active galactic nuclei (AGNs) up to z ∼ 2. Here, we focus on a sample of three AGNs with their host galaxies exhibiting prominent dust lanes, potentially due to their edge-on alignment. These represent 27% (3 out of 11 with early NIRCam data) of the heavily obscured (N H > 1023 cm−2) AGN population. With limited signs of a central AGN in the optical and near-infrared, the NIRCam images are used to produce reddening maps E(B − V) of the host galaxies. We compare the mean central value of E(B − V) to the X-ray obscuring column density along the line of sight to the AGN (N H ∼ 1023−23.5 cm−2). We find that the extinction due to the host galaxy is present (0.6 ≲ E(B − V) ≲ 0.9; 1.9 ≲ A V ≲ 2.8) and significantly contributes to the X-ray obscuration at a level of N H ∼ 1022.5 cm−2 assuming an SMC gas-to-dust ratio that amounts to ≲30% of the total obscuring column density. These early results, including three additional cases from CEERS, demonstrate the ability to resolve such dust structures with JWST and separate the different circumnuclear and galaxy-scale obscuring structures.

A Census of WISE-selected Dual and Offset AGNs Across the Sky: New Constraints on Merger-driven Triggering of Obscured AGNs

Pairs of galaxies hosting active galactic nuclei (AGNs) are powerful probes of merger-driven supermassive black hole (SMBH) growth as they can resolve individual AGNs and trace mergers over a large range of physical separations. To exploit this on a large scale for the first time for both obscured and unobscured AGNs, we use the photometric redshifts of AGNs selected by the Wide-field Infrared Survey Explorer (WISE) to find probabilistic pairs (<100 kpc separations) across the sky, along with a comparison sample of inactive galaxy pairs. Our final sample of integrated pair probabilities yields 198 AGN–AGN pairs (dual AGNs) and 2767 AGN–galaxy pairs (offset AGNs) with uniformly measured AGN and host galaxy physical properties. We find the fraction of galaxy pairs hosting WISE AGNs is dominated by offset AGNs and is significantly elevated above that of inactive galaxies for large host stellar masses. We show how the AGN merger fraction directly increases with AGN extinction for both offset and dual AGNs, with up to ∼40% of heavily obscured AGNs found in galaxy pairs. Elevated AGN merger fractions coincide with increased host specific star formation rates that suggest merger-driven coevolution of galaxies and SMBHs. Among dual AGNs, the most rapid SMBH growth may occur within the less-massive galaxy. Relative to stochastic mechanisms, mergers produce an excess of AGNs at increasingly smaller separations, especially for obscured AGNs (up to a factor of ∼5), and are augmented by correlated triggering. Finally, this excess is stronger than for lower-luminosity optically selected AGNs, regardless of the AGN obscuration level.

The Most Obscured AGNs in the XMM-SERVS Fields

We perform X-ray spectral analyses to derive the characteristics (e.g., column density, X-ray luminosity) of ≈10,200 active galactic nuclei (AGNs) in the XMM-Spitzer Extragalactic Representative Volume Survey, which was designed to investigate the growth of supermassive black holes across a wide dynamic range of cosmic environments. Using physical torus models (e.g., Borus02) and a Bayesian approach, we uncover 22 representative Compton-thick (CT; N H > 1.5 × 1024 cm−2) AGN candidates with good signal-to-noise ratios as well as a large sample of 136 heavily obscured AGNs. We also find an increasing CT fraction (f CT) from low (z < 0.75) to high (z > 0.75) redshift. Our CT candidates tend to show hard X-ray spectral shapes and dust extinction in their spectral energy distribution fits, which may shed light on the connection between AGN obscuration and host-galaxy evolution.

Large-scale clustering of buried X-ray AGN: Trends in AGN obscuration and redshift evolution

Aims. In order to test active galactic nucleus (AGN) unification and evolutionary models, we measured the AGN clustering properties as a function of AGN obscuration defined in terms of hydrogen column density, NH. In addition to measuring the clustering of unobscured (NH &lt; 1022 cm−2) and moderately obscured (1022 ≤ NH &lt; 1023.5) AGNs, we also targeted highly obscured sources (NH ≥ 1023.5) up to redshifts of z = 3. Methods. We have compiled one of the largest samples of X-ray-selected AGNs from a total of eight deep XMM/Chandra and multiwavelength surveys. We measured the clustering as a function of both AGN obscuration and redshift using the projected two-point correlation function, wp(rp). We modeled the large-scale clustering signal, measured the AGN bias, b(z, NH), and interpreted it in terms of the typical AGN host dark matter halo, Mhalo(z, NH). Results. We find no significant dependence of AGN clustering on obscuration, suggesting similar typical masses of the hosting halos as a function of NH. This result matches expectations of AGN unification models, in which AGN obscuration depends mainly on the viewing angle of the obscuring torus. We measured, for the first time, the clustering of highly obscured AGNs and find that these objects reside in halos with typical mass log Mhalo = 12.98−0.22+0.17[h−1 M⊙] (12.28−0.19+0.13) at low z ∼ 0.7 (high z ∼ 1.8) redshifts. We find that irrespective of obscuration, an increase in AGN bias with redshift is slower than the expectation for a constant halo mass and instead follows the growth rate of halos, known as the passive evolution track. This implies that for those AGNs the clustering is mainly driven by the mass growth rate of the hosting halos and galaxies across cosmic time.

Dusty plasma in active galactic nuclei

For many years we have known that dust in the form of a dusty-molecular torus is responsible for the obscuration in active galactic nuclei (AGN) at large viewing angles and, thus, for the widely used phenomenological classification of AGN. Recently, we gained new observational and theoretical insights into the geometry of the torus region and the role of dust in the dynamics of emerging outflows and failed winds. We will briefly touch on all these aspects and provide a more detailed update of our dust-based model (FRADO—Failed Radiatively Accelerated Dusty Outflow) capable of explaining the processes of formation of Balmer lines in AGN.Graphic abstract

On the Cosmic Evolution of AGN Obscuration and the X-Ray Luminosity Function: XMM-Newton and Chandra Spectral Analysis of the 31.3 deg2 Stripe 82X

We present X-ray spectral analysis of XMM-Newton and Chandra observations in the 31.3 deg2 Stripe-82X (S82X) field. Of the 6181 unique X-ray sources in this field, we analyze a sample of 2937 candidate active galactic nuclei (AGNs) with solid redshifts and sufficient counts determined by simulations. Our results show an observed population with median values of spectral index , column density log and intrinsic, de-absorbed, 2–10 keV luminosity log, in the redshift range 0–4. We derive the intrinsic, model-independent, fraction of AGNs that are obscured (), finding a significant increase in the obscured AGN fraction with redshift and a decline with increasing luminosity. The average obscured AGN fraction is 57% ± 4% for log L X/erg s−1 > 43. This work constrains the AGN obscuration and spectral shape of the still uncertain high-luminosity and high-redshift regimes (log L X/erg s−1 > 45.5, z > 3), where the obscured AGN fraction rises to 64% ± 12%. We report a luminosity and density evolution of the X-ray luminosity function, with obscured AGNs dominating at all luminosities at z > 2, and unobscured sources prevailing at log L X/erg s−1 > 45 at lower redshifts. Our results agree with the evolutionary models in which the bulk of AGN activity is triggered by gas-rich environments and in a downsizing scenario. Moreover, the black hole accretion density (BHAD) is found to evolve similarly to the star formation rate density, confirming the coevolution between AGN and host galaxy, but suggesting different timescales in their growing history. The derived BHAD evolution shows that Compton-thick AGNs contribute to the accretion history of AGNs as much as all other AGN populations combined.

The Obscured Fraction of Quasars at Cosmic Noon

Statistical studies of X-ray selected active galactic nuclei (AGN) indicate that the fraction of obscured AGN increases with increasing redshift, and the results suggest that a significant part of the accretion growth occurs behind obscuring material in the early universe. We investigate the obscured fraction of highly accreting X-ray AGN at around the peak epoch of supermassive black hole growth utilizing the wide and deep X-ray and optical/IR imaging data sets. A unique sample of luminous X-ray selected AGNs above z > 2 was constructed by matching the XMM-SERVS X-ray point-source catalog with a point-spread function convolved photometric catalog covering the u*–4.5 μm bands. Photometric redshift, hydrogen column density, and 2–10 keV AGN luminosity of the X-ray selected AGN candidates were estimated. Using the sample of 306 2–10 keV detected AGN at above redshift 2, we estimate the fraction of AGN with , assuming parametric X-ray luminosity and absorption functions. The results suggest that of luminous quasars () above redshift 2 are obscured. The fraction indicates an increased contribution of obscured accretion at high redshift than that in the local universe. We discuss the implications of the increasing obscured fraction with increasing redshift based on the AGN obscuration scenarios, which describe obscuration properties in the local universe. Both the obscured and unobscured z > 2 AGN show a broad range of SEDs and morphology, which may reflect the broad variety of host galaxy properties and physical processes associated with the obscuration.

Variability and Parameter Dependence of Hard X-Ray Obscuration Around Supermassive Black Holes in Active Galaxies

We investigate hard X-ray obscuration of Active Galactic Nuclei (AGNs) by considering photoionization processes for a number of simulated accretion-disk winds in our magnetohydrodynamic (MHD) framework. To follow up our earlier work on calculating synthetic AGN obscuration functions, we are motivated in this work to expand our examination of the dependences of obscuration on individual parameters associated with MHD wind and coronal X-ray such as: X-ray luminosity L ion, photon index Γ, density of the wind n o and its radial gradient p where n ∝ n o r −p . We find that AGN appear to undergo a relatively drastic transition from more obscured state (e.g., N H ≳ 1022 cm−2) to unobscured state (i.e., N H ≲ 1022 cm−2) as p approaches to ∼1.1 in these calculations. In the current formalism, luminosity is linearly coupled to wind density (i.e., L X ∝ n o ), and our calculations also indicate AGN become more obscured at higher luminosity. We further discuss the plausibility of the current model in comparison with observations.

BASS. XXI. The Data Release 2 Overview

The BAT AGN Spectroscopic Survey (BASS) is designed to provide a highly complete census of the key physical parameters of the supermassive black holes (SMBHs) that power local active galactic nuclei (AGNs) (z ≲ 0.3), including their bolometric luminosity (L bol), black hole (BH) mass (M BH), accretion rates (L bol/L Edd), line-of-sight gas obscuration (N H), and the distinctive properties of their host galaxies (e.g., star formation rates, masses, and gas fractions). We present an overview of the second data release of BASS (DR2), an unprecedented spectroscopic AGN survey in spectral range, resolution, and sensitivity, including 1449 optical (∼3200 Å–1 μm) and 233 near-IR (1–2.5 μm) spectra for the brightest 858 ultrahard X-ray (14–195 keV) selected AGNs across the entire sky and essentially all levels of obscuration. This release provides a highly complete set of key measurements (emission-line measurements and central velocity dispersions), with 99.9% measured redshifts and 98% BH masses estimated (for unbeamed AGNs outside the Galactic plane). The BASS DR2 AGN sample represents a unique census of nearby powerful AGNs, spanning over 5 orders of magnitude in AGN bolometric luminosity (L bol ∼ 1040–1047 erg s−1), BH mass (M BH ∼ 105–1010 M ⊙), Eddington ratio (L bol/L Edd ≳ 10−5), and obscuration (N H ∼ 1020–1025 cm−2). The public BASS DR2 sample and measurements can thus be used to answer fundamental questions about SMBH growth and its links to host galaxy evolution and feedback in the local universe, as well as open questions concerning SMBH physics. Here we provide a brief overview of the survey strategy, the key BASS DR2 measurements, data sets and catalogs, and scientific highlights from a series of DR2-based works pursued by the BASS team.

X-Ray Obscuration around Supermassive Black Holes in Active Galaxies

We investigate obscuration of Active Galactic Nuclei (AGNs), identified as Supermassive Black Holes (BH) in luminous galaxies. In this model, winds of plasma particles launched from the accretion disk are photoionized by hard X-ray continua from the AGN’s corona, resulting in obscuration in the X-ray band. Many X-ray spectroscopic observations suggest a majority of AGN are obscured by an intervening gas along our line of sight. Through photoionization calculations for selected wind solutions, we simulate the observed AGN obscuration distribution. We discuss the plausibility of the model by comparing our theoretical obscuration distribution to X-ray data by producing a library of synthetic absorption spectra of X-ray continua. Using our model’s obscuration findings, we show how the obscuration distribution is dependent on the model parameters.

The Black Hole–Galaxy Connection: Interplay between Feedback, Obscuration, and Host Galaxy Substructure

Abstract There is growing evidence for physical influence between supermassive black holes and their host galaxies. We present a case study of the nearby galaxy NGC 7582, for which we find evidence that galactic substructure plays an important role in affecting the collimation of ionized outflows as well as contributing to the heavy active galactic nucleus (AGN) obscuration. This result contrasts with a simple, small-scale AGN torus model, according to which AGN-wind collimation may take place inside the torus itself, at subparsec scales. Using 3D spectroscopy with the Multi Unit Spectroscopic Explorer instrument, we probe the kinematics of the stellar and ionized gas components as well as the ionization state of the gas from a combination of emission-line ratios. We report for the first time a kinematically distinct core (KDC) in NGC 7582, on a scale of ∼600 pc. This KDC coincides spatially with dust lanes and starbursting complexes previously observed. We interpret it as a circumnuclear ring of stars and dusty, gas-rich material. We obtain a clear view of the outflowing cones over kiloparsec scales and demonstrate that they are predominantly photoionized by the central engine. We detect the back cone (behind the galaxy) and confirm previous results of a large nuclear obscuration of both the stellar continuum and H ii regions. While we tentatively associate the presence of the KDC with a large-scale bar and/or a minor galaxy merger, we stress the importance of gaining a better understanding of the role of galaxy substructure in controlling the fueling, feedback, and obscuration of AGNs.

A Catalog of Host Galaxies for WISE-selected AGN: Connecting Host Properties with Nuclear Activity and Identifying Contaminants

Abstract We present a catalog of physical properties for galaxies hosting active galactic nuclei (AGN) detected by the Wide-field Infrared Survey Explorer (WISE). By fitting broadband spectral energy distributions of sources in the WISE AGN Catalog with empirical galaxy and AGN templates, we derive photometric redshifts, AGN bolometric luminosities, measures of AGN obscuration, host galaxy stellar masses, and host galaxy star formation rates (SFRs) for 695,273 WISE AGN. The wide-area nature of this catalog significantly augments the known number of obscured AGN out to redshifts z ∼ 3 and will be useful for studies focused on AGN or their host galaxy physical properties. We first show that the most likely non-AGN contaminants are galaxies at redshifts z = 0.2–0.3, with relatively blue W1–W2 colors, and with high specific SFRs for which the dust continuum emission is elevated in the W2 filter. Toward increasingly lower redshifts, WISE AGN host galaxies have systematically lower specific SFRs relative to those of normal star-forming galaxies, likely due to decreased cold gas fractions and the time delay between global star formation and AGN triggering. Finally, WISE AGN obscuration is not strongly correlated with AGN bolometric luminosity but shows a significant negative correlation with the Eddington ratio. This result is consistent with a version of the receding torus model in which the obscuring material is located within the supermassive black hole gravitational sphere of influence and the dust inner radius increases due to radiation pressure.