Growth Of Supermassive Black Holes Research Articles

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.

An X-ray fading, UV brightening QSO at z ≈ 6

Explaining the existence of super massive black holes (SMBHs) with MBH ≳ 108 M⊙ at z ≳ 6 is a persistent challenge to modern astrophysics. Multiwavelength observations of z ≳ 6 quasi-stellar objects (QSOs) reveal that, on average, their accretion physics is similar to that of their counterparts at lower redshift. However, QSOs showing properties that deviate from the general behavior can provide useful insights into the physical processes responsible for the rapid growth of SMBHs in the early universe. We present X-ray (XMM-Newton, 100 ks) follow-up observations of a z ≈ 6 QSO, J1641+3755, which was found to be remarkably X-ray bright in a 2018 Chandra dataset. J1641+3755 is not detected in the 2021 XMM-Newton observation, implying that its X-ray flux decreased by a factor ≳7 on a notably short timescale (i.e., ≈115 rest-frame days), making it the z > 4 QSO with the largest variability amplitude. We also obtained rest-frame ultraviolet (UV) spectroscopic and photometric data with the Large Binocular Telescope (LBT). Surprisingly, comparing our LBT photometry with archival data, we found that J1641+3755 became consistently brighter in the rest-frame UV band from 2003 to 2016, while no strong variation occurred from 2016 to 2021. Its rest-frame UV spectrum is consistent with the average spectrum of high-redshift QSOs. Multiple narrow absorption features are present, and several of them can be associated with an intervening system at z = 5.67. Several physical causes can explain the variability properties of J1641+3755, including intrinsic variations of the accretion rate, a small-scale obscuration event, gravitational lensing due to an intervening object, and an unrelated X-ray transient in a foreground galaxy in 2018. Accounting for all of the z > 6 QSOs with multiple X-ray observations separated by more that ten rest-frame days, we found an enhancement of strongly (i.e., by a factor > 3) X-ray variable objects compared to QSOs at later cosmic times. This finding may be related to the physics of fast accretion in high-redshift QSOs.

The Close AGN Reference Survey (CARS)

Context. The host galaxy conditions for rapid supermassive black hole growth are poorly understood. Narrow-line Seyfert 1 (NLS1) galaxies often exhibit high accretion rates and are hypothesized to be prototypes of active galactic nuclei (AGN) at an early stage of their evolution. Aims. We present adaptive optics (AO) assisted VLT MUSE NFM observations of Mrk 1044, the nearest super-Eddington accreting NLS1. Together with archival MUSE WFM data, we aim to understand the host galaxy processes that drive Mrk 1044’s black hole accretion. Methods. We extracted the faint stellar continuum emission from the AGN-deblended host and performed spatially resolved emission line diagnostics with an unprecedented resolution. Combining both MUSE WFM and NFM-AO observations, we used a kinematic model of a thin rotating disk to trace the stellar and ionized gas motion from 10 kpc galaxy scales down to ∼30 pc around the nucleus. Results. Mrk 1044’s stellar kinematics follow circular rotation, whereas the ionized gas shows tenuous spiral features in the center. We resolve a compact star-forming circumnuclear ellipse (CNE) that has a semi-minor axis of 306 pc. Within this CNE, the gas is metal-rich and its line ratios are entirely consistent with excitation by star formation. With an integrated star formation rate of 0.19 ± 0.05 M⊙ yr−1, the CNE contributes 27% of the galaxy-wide star formation. Conclusions. We conclude that Mrk 1044’s nuclear activity has not yet affected the circumnuclear star formation. Thus, Mrk 1044 is consistent with the idea that NLS1s are young AGN. A simple mass budget consideration suggests that the circumnuclear star formation and AGN phase are connected and the patterns in the ionized gas velocity field are a signature of the ongoing AGN feeding.

Cold Gas Reservoirs of Low- and High-mass Central Galaxies Differ in Response to Active Galactic Nucleus Feedback

The growth of supermassive black holes, especially the associated state of active galactic nuclei (AGNs), is generally believed to be the key step in regulating star formation in massive galaxies. As the fuel of star formation, the cold gas reservoir is a direct probe of the effect of AGN feedback on their host galaxies. However, in observations, no clear connection has been found between AGN activity and the cold gas mass. In this paper, we find observational signals of the significant depletion of the total neutral hydrogen gas reservoir in optically selected Type 2 AGN-host central galaxies of stellar mass 109–1010 M ⊙. The effect of AGN feedback on the cold gas reservoir is stronger for higher star formation rates and higher AGN luminosity. But it becomes much weaker above this mass range, consistent with previous findings focusing on massive galaxies. Our result suggests that low-mass and gas-rich AGN-host central galaxies would first form dense cores before AGN feedback is triggered, removing their neutral hydrogen gas. More massive central galaxies may undergo a significantly different formation scenario by gradually building up dense cores with less effective and recurrent AGN feedback.

Galaxy mergers can initiate quenching by unlocking an AGN-driven transformation of the baryon cycle

ABSTRACT We use zoom simulations to show how merger-driven disruption of the gas disc in a galaxy provides its central active galactic nucleus (AGN) with fuel to drive outflows that entrain and expel a significant fraction of the circumgalactic medium (CGM). This in turn suppresses replenishment of the interstellar medium, causing the galaxy to quench up to several Gyr after the merger. We start by performing a zoom simulation of a present-day star-forming disc galaxy with the EAGLE galaxy formation model. Then, we re-simulate the galaxy with controlled changes to its initial conditions, using the genetic modification technique. These modifications either increase or decrease the stellar mass ratio of the galaxy’s last significant merger, which occurs at $z$ ≈ 0.74. The halo reaches the same present-day mass in all cases, but changing the mass ratio of the merger yields markedly different galaxy and CGM properties. We find that a merger can unlock rapid growth of the central supermassive black hole if it disrupts the co-rotational motion of gas in the black hole’s vicinity. Conversely, if a less disruptive merger occurs and gas close to the black hole is not disturbed, the AGN does not strongly affect the CGM, and consequently the galaxy continues to form stars. Our result illustrates how a unified view of AGN feedback, the baryon cycle and the interstellar medium is required to understand how mergers and quenching are connected over long time-scales.

The Age of Discovery with the James Webb Space Telescope: Excavating the Spectral Signatures of the First Massive Black Holes

The James Webb Space Telescope (JWST) will open a new window into the most distant universe and unveil the early growth of supermassive black holes (BHs) in the first galaxies. In preparation for deep JWST imaging surveys, it is crucial to understand the color selection of high-redshift accreting seed BHs. We model the spectral energy distribution of super-Eddington accreting BHs with millions of solar masses in metal-poor galaxies at z ≳ 8, applying postprocess line transfer calculations to radiation hydrodynamical simulation results. Exposures of 10 ks with the NIRCam and MIRI broadband filters are sufficient to detect the radiation flux from the seed BHs with bolometric luminosities of L bol ≃ 1045 erg s−1. While the continuum colors are similar to those of typical low-z quasars, strong Hα line emission with a rest-frame equivalent width EWrest ≃ 1300 Å is so prominent that the line flux affects the broadband colors significantly. The unique colors, for instance, F356W − F560W ≳ 1 at 7 < z < 8 and F444W − F770W ≳ 1 at 9 < z < 12, provide robust criteria for photometric selection of rapidly growing seed BHs. Moreover, NIRSpec observations of low-ionization emission lines can test whether the BH is fed via a dense accretion disk at super-Eddington rates.

Feedback effect on the observable properties of z &amp;gt; 6 AGN

ABSTRACT Active galactic nuclei (AGNs) feedback has a major impact on to the supermassive black hole (SMBH) growth, the properties of the host galaxies, and their cosmic evolution. We investigate the effects of different kinetic feedback prescriptions on the observable properties of AGN and their host galaxies at z &amp;gt; 6 in a suite of zoom-in cosmological simulations. We find that kinetic feedback decreases the column density of the interstellar medium (ISM) in the host galaxy by up to a factor of ≈10, especially when the SMBHs reach high accretion rates ($\approx 10{-}30\, \mathrm{M_\odot \, yr^{-1}}$). In particular, kinetic feedback is required to extend the ISM size to &amp;gt;1 kpc and match the observed sizes of the gas reservoirs in z &amp;gt; 6 AGN host galaxies. Moreover, it produces unobscured lines of sight along which the AGN can be detected in the rest-frame UV band with magnitudes consistent with observed values of z &amp;gt; 6 AGN. The assumed geometry of the outflow plays an important role in shaping the observed properties of high-redshift AGN. We find that a biconical geometry is favoured over a spherical one to reproduce the observed properties, but it overestimates the number of multiple AGN systems detectable in X-ray observations. This result suggests that simplistic BH seeding recipes widely employed in cosmological simulations produce too many X-ray detectable multiple AGN at z = 6−7, thus soliciting the adoption of more physically motivated seeding prescriptions.

The importance of black hole repositioning for galaxy formation simulations

ABSTRACT Active galactic nucleus (AGN) feedback from accreting supermassive black holes (SMBHs) is an essential ingredient of galaxy formation simulations. The orbital evolution of SMBHs is affected by dynamical friction that cannot be predicted self-consistently by contemporary simulations of galaxy formation in representative volumes. Instead, such simulations typically use a simple ‘repositioning’ of SMBHs, but the effects of this approach on SMBH and galaxy properties have not yet been investigated systematically. Based on a suite of smoothed particle hydrodynamics simulations with the swift code and a Bondi-Hoyle-Lyttleton sub-grid gas accretion model, we investigate the impact of repositioning on SMBH growth and on other baryonic components through AGN feedback. Across at least a factor ∼1000 in mass resolution, SMBH repositioning (or an equivalent approach) is a necessary prerequisite for AGN feedback; without it, black hole growth is negligible. Limiting the effective repositioning speed to ≲10 km s−1 delays the onset of AGN feedback and severely limits its impact on stellar mass growth in the centre of massive galaxies. Repositioning has three direct physical consequences. It promotes SMBH mergers and thus accelerates their initial growth. In addition, it raises the peak density of the ambient gas and reduces the SMBH velocity relative to it, giving a combined boost to the accretion rate that can reach many orders of magnitude. Our results suggest that a more sophisticated and/or better calibrated treatment of SMBH repositioning is a critical step towards more predictive galaxy formation simulations.

On the Connection between Supermassive Black Holes and Galaxy Growth in the Reionization Epoch

The correlation between the mass of supermassive black holes (SMBHs; ) and their host galaxies () in the reionization epoch provides valuable constraints on their early growth. High-redshift quasars typically have an / ratio significantly elevated in comparison to the local value. However, the degree to which this apparent offset is driven by observational biases is unclear for the most distant quasars. To address this issue, we model the sample selection and measurement biases for a compilation of 20 quasars at z ∼ 6 with host properties based on ALMA observations. We find that the observed distribution of quasars in the plane can be reproduced by assuming that the underlying SMBH population at z ∼ 6 follows the relationship in the local universe. However, a positive or even a negative evolution in / can also explain the data, depending on whether the intrinsic scatter evolves and on the strength of various systematic uncertainties. To break these degeneracies, an improvement in the accuracy of mass measurements and an expansion of the current sample to lower limits are needed. Furthermore, assuming a radiative efficiency of 0.1 and quasar duty cycles estimated from the active SMBH fraction, significant outliers in / tend to move toward the local relation given their instantaneous BH growth rate and star formation rate. This may provide evidence for a self-regulated SMBH–galaxy coevolution scenario that is in place at z ∼ 6, with active galactic nucleus feedback being a possible driver.

Ejection–accretion connection in NLS1 AGN 1H 1934-063

ABSTRACT Accretion and ejection of matter in active galactic nuclei (AGNs) are tightly connected phenomena and represent fundamental mechanisms regulating the growth of the central supermassive black hole and the evolution of the host galaxy. However, the exact physical processes involved are not yet fully understood. We present a high-resolution spectral analysis of a simultaneous XMM–Newton and NuSTAR observation of the narrow line Seyfert 1 (NLS1) AGN 1H 1934-063, during which the X-ray flux dropped by a factor of ∼6 and subsequently recovered within 140 kiloseconds. By means of the time-resolved and flux-resolved X-ray spectroscopy, we discover a potentially variable warm absorber and a relatively stable ultra-fast outflow (UFO, $v_\mathrm{UFO}\sim -0.075\, c$) with a mild ionization state ($\log (\xi /\mathrm{erg\, cm\, s^{-1})}\sim 1.6$). The detected emission lines (especially a strong and broad feature around 1 keV) are of unknown origin and cannot be explained with emission from plasmas in photo- or collisional-ionization equilibrium. Such emission lines could be well described by a strongly blueshifted (z ∼ −0.3) secondary reflection off the base of the equatorial outflows, which may reveal the link between the reprocessing of the inner accretion flow photons and the ejection. However, this scenario although being very promising is only tentative and will be tested with future observations.

The Contribution of AGN Accretion Disks to Hydrogen Reionization

Abstract We examine the contribution of high-redshift (z &gt; 6) active galactic nuclei (AGNs) to cosmic hydrogen reionization, by tracing the growth and ionizing output of the first generation of supermassive black holes (SMBHs). Our calculations are anchored to the observed population of z ≃ 6 quasars, and trace back the evolving spectral energy distributions (SEDs) of the accretion flows that power these early AGNs and consider a variety of growth histories, including super-Eddington accretion. Compared to a fixed-shape SED, the evolving thin disks produce ionizing radiation that is higher by up to ∼80%. Across a variety of SMBH growth scenarios, the contribution of AGNs to reionization is limited to late epochs (z &lt; 7), and remains subdominant compared to star-forming galaxies. This conclusion holds irrespective of the (still unknown) space density of low-luminosity z = 6 AGNs, and for growth scenarios that allow super-Eddington accretion. The contribution of AGNs to reionization can extend to earlier epochs (z ≳ 8) in scenarios with relatively slow SMBH mass growth, i.e., for low accretion rates and/or high spins. We finally demonstrate that our framework can reproduce the observed quasar proximity-zone sizes, and that compact proximity zones around z = 6 quasars can be explained by the late onset of super-Eddington accretion.

Central engine of the highest redshift blazar

We present the results of a new LUCI/Large Binocular Telescope near-infrared (NIR) spectroscopic observation of PSO J030947.49+271757.31 (hereafter PSO J0309+27), the highest redshift blazar known to date (z ∼ 6.1). From the CIV λ1549 broad emission line, we found that PSO J0309+27 is powered by a 1.45−0.85+1.89 × 109 M⊙ supermassive black hole (SMBH) with a bolometric luminosity of ∼8 × 1046 erg s−1 and an Eddington ratio equal to 0.44−0.35+0.78. We also obtained new photometric observations with the Telescopio Nazionale Galileo in J and K bands to better constrain the NIR spectral energy distribution of the source. Thanks to these observations, we were able to model the accretion disk and to derive an independent estimate of the black hole mass of PSO J0309+27, confirming the value inferred from the virial technique. The existence of such a massive SMBH just ∼900 million years after the Big Bang challenges models of the earliest SMBH growth, especially if jetted active galactic nuclei are indeed associated with a highly spinning black hole, as is currently assumed. In a Eddington-limited accretion scenario and assuming a radiative efficiency of 0.3, typical of a fast rotating SMBH, a seed black hole of more than 106 M⊙ at z = 30 is indeed required to reproduce the mass of PSO J0309+27 at a redshift of 6. This requirement suggests either earlier periods of rapid black hole growth with super-Eddington accretion or a scenario in which only part of the released gravitational energy goes toward heating the accretion disk and feeding the black hole.

Revealing new high-redshift quasar populations through Gaussian mixture model selection

We present a novel method for identifying candidate high-redshift quasars (HzQs; z ≳ 5.5) –which are unique probes of supermassive black hole growth in the early Universe– from large-area optical and infrared photometric surveys. Using Gaussian mixture models to construct likelihoods and incorporating informed priors based on population statistics, our method uses a Bayesian framework to assign posterior probabilities that differentiate between HzQs and contaminating sources. We additionally include deep radio data to obtain informed priors. Using existing HzQ data in the literature, we set a posterior threshold that accepts ∼90% of known HzQs while rejecting &gt; 99% of contaminants such as dwarf stars or lower redshift galaxies. Running the probability selection on test samples of simulated HzQs and contaminants, we find that the efficacy of the probability method is higher than traditional colour cuts, decreasing the fraction of accepted contaminants by 86% while retaining a similar fraction of HzQs. As a test, we apply our method to the Pan-STARRS Data Release 1 (PS1) source catalogue within the HETDEX Spring field area on the sky, covering 400 sq. deg. and coinciding with deep radio data from the LOFAR Two-metre Sky Survey Data Release 1. From an initial sample of ∼5 × 105 sources in PS1, our selection shortlists 251 candidate HzQs, which are further reduced to 63 after visual inspection. Shallow spectroscopic follow-up of 13 high-probability HzQs resulted in the confirmation of a previously undiscovered quasar at z = 5.66 with photometric colours i − z = 1.4, lying outside the typically probed regions when selecting HzQs based on colours. This discovery demonstrates the efficacy of our probabilistic HzQ selection method in selecting more complete HzQ samples, which holds promise when employed on large existing and upcoming photometric data sets.

HARMONI view of the host galaxies of active galactic nuclei around cosmic noon

Context. The formation and evolution of galaxies appear linked to the growth of supermassive black holes, as evidenced by empirical scaling relations in nearby galaxies. Understanding this co-evolution over cosmic time requires the revelation of the dynamical state of galaxies and the measurement of the mass of their central black holes (MBH) at a range of cosmic distances. Bright active galactic nuclei (AGNs) are ideal for this purpose. Aims. The High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI), the first light integral-field spectrograph for the Extremely Large Telescope, will transform visible and near-infrared ground-based astrophysics thanks to its advances in sensitivity and angular resolution. We aim to analyse the capabilities of HARMONI to reveal the stellar morpho-kinematic properties of the host galaxies of AGNs at about cosmic noon. Methods. We made use of the simulation pipeline for HARMONI (HSIM) to create mock observations of representative AGN host galaxies at redshifts around cosmic noon. We used observations taken with the Multi Unit Spectroscopic Explorer of nearby galaxies showing different morphologies and dynamical stages combined with theoretical AGN spectra to create the target inputs for HSIM. Results. According to our simulations, an on-source integration time of three hours should be enough to measure the MBH and to trace the morphology and stellar kinematics of the brightest host galaxies of AGNs beyond cosmic noon. For host galaxies with stellar masses &lt; 1011 M⊙, longer exposure times are mandatory to spatially resolve the stellar kinematics.

Running late: testing delayed supermassive black hole growth models against the quasar luminosity function

ABSTRACT Observations of massive galaxies at low redshift have revealed approximately linear scaling relations between the mass of a supermassive black hole (SMBH) and properties of its host galaxy. How these scaling relations evolve with redshift and whether they extend to lower-mass galaxies, however, remain open questions. Recent galaxy formation simulations predict a delayed, or ‘two-phase,’ growth of SMBHs: slow, highly intermittent BH growth due to repeated gas ejection by stellar feedback in low-mass galaxies, followed by more sustained gas accretion that eventually brings BHs on to the local scaling relations. The predicted two-phase growth implies a steep increase, or ‘kink,’ in BH-galaxy scaling relations at a stellar mass $\rm {M}_{*}\sim 5\times 10^{10}$ M⊙. We develop a parametric, semi-analytic model to compare different SMBH growth models against observations of the quasar luminosity function (QLF) at z ∼ 0.5−4. We compare models in which the relation between SMBH mass and galaxy mass is purely linear versus two-phase models. The models are anchored to the observed galaxy stellar mass function, and the BH mass functions at different redshifts are consistently connected by the accretion rates contributing to the QLF. The best fits suggest that two-phase evolution is significantly preferred by the QLF data over a purely linear scaling relation. Moreover, when the model parameters are left free, the two-phase model fits imply a transition mass consistent with that predicted by simulations. Our analysis motivates further observational tests, including measurements of BH masses and active galactic nuclei activity at the low-mass end, which could more directly test two-phase SMBH growth.

The low-end of the black hole mass function at cosmic dawn

ABSTRACT Understanding the formation and growth of supermassive black holes (SMBHs) at high redshift represents a major challenge for theoretical models. In this work, we investigate the early evolution of the first SMBHs by constraining their distribution in mass and luminosity at z &amp;gt; 4. In particular, we focus on the poorly explored low-mass end of the nuclear black hole (BH) distribution down to z ≃ 4, and explore its connection with the nature of the first BH seeds and the processes governing their mass growth. To this aim, we have developed CAT (Cosmic Archaeology Tool), a new semi-analytic model that describes the formation of the first stars and BHs in a self-consistent way and follows the co-evolution of nuclear BHs and their host galaxies for a representative population at z &amp;gt; 4. We find that current observational constraints favour models where the growth of BH seeds is Eddington limited and occurs at the Bondi–Hoyle–Lyttleton rate or where super-Eddington accretion occurs via a slim disc during gas-rich galaxy mergers. The main difference between these two model variants lies at the low end of the predicted mass and luminosity functions at 4 ≤ z ≤ 6, where a clear gap appears in the first model, reflecting the stunted growth of light BH seeds formed as remnants of the first stars. Detecting this signature will be extremely challenging even for the future generation of space observatories, such as JWST, Athena, and Lynx.

Black hole–galaxy scaling relations in FIRE: the importance of black hole location and mergers

ABSTRACT The concurrent growth of supermassive black holes (SMBHs) and their host galaxies remains to be fully explored, especially at high redshift. While often understood as a consequence of self-regulation via AGN feedback, it can also be explained by alternative SMBH accretion models. Here, we expand on previous work by studying the growth of SMBHs with the help of a large suite of cosmological zoom-in simulations (MassiveFIRE) that are part of the Feedback in Realistic Environments (FIRE) project. The growth of SMBHs is modelled in post-processing with different black hole accretion models, placements, and merger treatments, and validated by comparing to on-the-fly calculations. Scaling relations predicted by the gravitational torque-driven accretion (GTDA) model agree with observations at low redshift without the need for AGN feedback, in contrast to models in which the accretion rate depends strongly on SMBH mass. At high redshift, we find deviations from the local scaling relations in line with previous theoretical results. In particular, SMBHs are undermassive, presumably due to stellar feedback, but start to grow efficiently once their host galaxies reach M* ∼ 1010M⊙. We analyse and explain these findings in the context of a simple analytic model. Finally, we show that the predicted scaling relations depend sensitively on the SMBH location and the efficiency of SMBH merging, particularly in low-mass systems. These findings highlight the relevance of understanding the evolution of SMBH-galaxy scaling relations to predict the rate of gravitational wave signals from SMBH mergers across cosmic history.

Consistent Analysis of the AGN LF in X-Ray and MIR in the XMM-LSS Field

Abstract The luminosity function of active galactic nuclei (AGN) probes the history of supermassive black hole assembly and growth across cosmic time. To mitigate selection biases, we present a consistent analysis of the AGN luminosity functions (LFs) derived for both X-ray and mid-infrared (MIR) selected AGN in the XMM-Large Scale Structure field. There are 4268 AGN used to construct the MIR luminosity function (IRLF) and 3427 AGN used to construct the X-ray luminosity function (XLF), providing the largest census of the AGN population out to z = 4 in both bands with significant reduction in uncertainties. We are able for the first time to see the knee of the IRLF at z &gt; 2 and observe a flattening of the faint-end slope as redshift increases. The bolometric luminosity density, a proxy for the cosmic black hole accretion history, computed from our LFs, shows a peak at z ≈ 2.25, consistent with recent estimates of the peak in the star formation rate density (SFRD). However, at earlier epochs, the AGN luminosity density is flatter than the SFRD. If confirmed, this result suggests that the build up of black hole mass outpaces the growth of stellar mass in high-mass systems at z ≳ 2.5. This is consistent with observations of redshift z ∼ 6 quasars that lie above the local M − σ relationship. The luminosity density derived from the IRLF is higher than that from the XLF at all redshifts. This is consistent with the dominant role of obscured AGN activity in the cosmic growth of supermassive black holes.

ALCHEMI, an ALMA Comprehensive High-resolution Extragalactic Molecular Inventory

Context.The interstellar medium is the locus of physical processes affecting the evolution of galaxies which drive or are the result of star formation activity, supermassive black hole growth, and feedback. The resulting physical conditions determine the observable chemical abundances that can be explored through molecular emission observations at millimeter and submillimeter wavelengths.Aims.Our goal is to unveiling the molecular richness of the central region of the prototypical nearby starburst galaxy NGC 253 at an unprecedented combination of sensitivity, spatial resolution, and frequency coverage.Methods.We used the Atacama Large Millimeter/submillimeter Array (ALMA), covering a nearly contiguous 289 GHz frequency range between 84.2 and 373.2 GHz, to image the continuum and spectral line emission at 1.6″(∼28 pc) resolution down to a sensitivity of 30 − 50 mK. This article describes the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) large program. We focus on the analysis of the spectra extracted from the 15″ (∼255 pc) resolution ALMA Compact Array data.Results.We modeled the molecular emission assuming local thermodynamic equilibrium with 78 species being detected. Additionally, multiple hydrogen and helium recombination lines are identified. Spectral lines contribute 5 to 36% of the total emission in frequency bins of 50 GHz. We report the first extragalactic detections of C2H5OH, HOCN, HC3HO, and several rare isotopologues. Isotopic ratios of carbon, oxygen, sulfur, nitrogen, and silicon were measured with multiple species.Concluison.Infrared pumped vibrationaly excited HCN, HNC, and HC3N emission, originating in massive star formation locations, is clearly detected at low resolution, while we do not detect it for HCO+. We suggest high temperature conditions in these regions driving a seemingly “carbon-rich” chemistry which may also explain the observed high abundance of organic species close to those in Galactic hot cores. TheLvib/LIRratio was used as a proxy to estimate a 3% contribution from the proto super star cluster to the global infrared emission. Measured isotopic ratios with high dipole moment species agree with those within the central kiloparsec of the Galaxy, while those derived from13C/18O are a factor of five larger, confirming the existence of multiple interstellar medium components within NGC 253 with different degrees of nucleosynthesis enrichment. The ALCHEMI data set provides a unique template for studies of star-forming galaxies in the early Universe.

A Catalog of 204 Offset and Dual Active Galactic Nuclei (AGNs): Increased AGN Activation in Major Mergers and Separations under 4 kpc

Abstract During galaxy mergers, gas and dust are driven toward the centers of merging galaxies, triggering enhanced star formation and supermassive black hole (SMBH) growth. Theory predicts that this heightened activity peaks at SMBH separations &lt;20 kpc; if sufficient material accretes onto one or both of the SMBHs for them to become observable as active galactic nuclei (AGNs) during this phase, they are known as offset and dual AGNs, respectively. To better study these systems, we have built the ACS-AGN Merger Catalog, a large catalog (N = 204) of uniformly selected offset and dual AGN observed by the Hubble Space Telescope at 0.2 &lt; z &lt; 2.5 with separations &lt;20 kpc. Using this catalog, we answer many questions regarding SMBH−galaxy coevolution during mergers. First, we confirm predictions that the AGN fraction peaks at SMBH pair separations &lt;10 kpc; specifically, we find that the fraction increases significantly at pair separations of &lt;4 kpc. Second, we find that AGNs in mergers are preferentially found in major mergers and that the fraction of AGNs found in mergers follows a logarithmic relation, decreasing as merger mass ratio increases. Third, we do not find that mergers (nor the major or minor merger subpopulations) trigger the most luminous AGNs. Finally, we find that nuclear column density, AGN luminosity, and host galaxy star formation rate have no dependence on SMBH pair separation or merger mass ratio in these systems, nor do the distributions of these values differ significantly from that of the overall AGN population.