Growth Of Supermassive Black Holes Research Articles

The Cosmic Evolution of the Supermassive Black Hole Population: A Hybrid Observed Accretion and Simulated Mergers Approach

Supermassive black holes (SMBHs) can grow through both accretion and mergers. It is still unclear how SMBHs evolve under these two channels from high redshifts to the SMBH population we observe in the local Universe. Observations can directly constrain the accretion channel but cannot effectively constrain mergers yet, while cosmological simulations provide galaxy merger information but can hardly return accretion properties consistent with observations. In this work, we combine the observed accretion channel and the simulated merger channel, taking advantage of observations and cosmological simulations, to depict a realistic evolution pattern of the SMBH population. With this methodology, we can derive the scaling relation between the black hole mass (M BH) and host-galaxy stellar mass (M ⋆), and the local black hole mass function (BHMF). Our scaling relation is lower than those based on dynamically measured M BH, supporting the claim that dynamically measured SMBH samples may be biased. We show that the scaling relation has little redshift evolution. The BHMF steadily increases from z = 4 to z = 1 and remains largely unchanged from z = 1 to z = 0. The overall SMBH growth is generally dominated by the accretion channel, with possible exceptions at high mass (M BH ≳ 108 M ⊙ or M ⋆ ≳ 1011 M ⊙) and low redshift (z ≲ 1). We also predict that around 25% of the total SMBH mass budget in the local Universe may be locked within long-lived, wandering SMBHs, and the wandering mass fraction and wandering SMBH counts increase with M ⋆.

On the origin of star formation quenching in massive galaxies at ≳ in the cosmological simulations IllustrisTNG

ABSTRACT Using the cosmological simulations IllustrisTNG, we perform a comprehensive analysis of quiescent, massive galaxies at $z \gtrsim 3$. The goal is to understand what suppresses their star formation so early in cosmic time, and how other similar mass galaxies remain highly star forming. As a first-order result, the simulations are able to produce massive, quiescent galaxies in this high-redshift regime. We find that active galactic nucleus (AGN) feedback is the primary cause of halting star formation in early, massive galaxies. Not only do the central, supermassive black holes (SMBHs) of the quenched galaxies have earlier seed times, but they also grow faster than in star-forming galaxies. As a result, the quenched galaxies are exposed to AGN feedback for longer, and experience the kinetic, jet mode of the AGN feedback earlier than the star-forming galaxies. The release of kinetic energy reduces inflows of gas while likely maintaining outflows, which keeps a low cold gas fraction and decreases the star formation of the galaxies down to a state of quiescence. In addition to AGN feedback, we also investigate the influence of the large-scale environment. While mergers do not play a significant role in the quenching process, the quenched galaxies tend to reside in more massive haloes and denser regions during their evolution. As this provides a greater initial amount of infalling gas to the galaxies, the large-scale environment can mildly affect the fate of the central SMBH growth and, via AGN feedback, contribute to star formation quenching.

An Estimate of the Impact of Reionization on Supermassive Black Hole Growth

The supermassive black holes (SMBHs) that power active galactic nuclei found at z ≥ 6 were formed during the Epoch of Reionization. Because reionization is an inhomogeneous process, the physical properties of SMBH host-galaxy environments will vary spatially during reionization. We construct a semi-analytic model to estimate the impact of reionization on SMBH growth. Using a series of merger trees, reionization models, and black hole (BH) growth models, we find that early reionization can reduce a SMBH’s mass by up to [50, 70, 90]% within dark matter halos of mass [1012, 1011, 1010] M ⊙ by z = 6. Our findings also suggest that the redshift range in which BH growth is impacted by reionization strongly depends on whether the Eddington accretion rate can be exceeded. If so, we find that BH masses are significantly suppressed principally during the early phases of reionization (z ≳ 10), while they are more readily suppressed across the full redshift range if super-Eddington growth is not allowed. We find that the global average impact of reionization may be to reduce the masses of BHs residing in ≲1011 M ⊙ halos by a factor of ≳2. The census of SMBHs being uncovered by the JWST may offer a means to test the basic prediction that more massive BHs reside in cosmological volumes that are reionized at later times.

EIGER. VI. The Correlation Function, Host Halo Mass, and Duty Cycle of Luminous Quasars at z ≳ 6

We expect luminous (M 1450 ≲ −26.5) high-redshift quasars to trace the highest-density peaks in the early Universe. Here, we present observations of four z ≳ 6 quasar fields using JWST/NIRCam in the imaging and wide-field slitless spectroscopy mode and report a wide range in the number of detected [O iii]-emitting galaxies in the quasars’ environments, ranging between a density enhancement of δ ≈ 65 within a 2 cMpc radius—one of the largest protoclusters during the Epoch of Reionization discovered to date—to a density contrast consistent with zero, indicating the presence of a UV-luminous quasar in a region comparable to the average density of the Universe. By measuring the two-point cross-correlation function of quasars and their surrounding galaxies, as well as the galaxy autocorrelation function, we infer a correlation length of quasars at 〈z〉 = 6.25 of r0QQ=22.0−2.9+3.0cMpch−1 , while we obtain a correlation length of the [O iii]-emitting galaxies of r0GG=4.1±0.3cMpch−1 . By comparing the correlation functions to dark-matter-only simulations we estimate the minimum mass of the quasars’ host dark matter halos to be log10(Mhalo,min/M⊙)=12.43−0.15+0.13 (and log10(Mhalo,min[OIII]/M⊙)=10.56−0.03+0.05 for the [O iii] emitters), indicating that (a) luminous quasars do not necessarily reside within the most overdense regions in the early Universe, and that (b) the UV-luminous duty cycle of quasar activity at these redshifts is f duty ≪ 1. Such short quasar activity timescales challenge our understanding of early supermassive black hole growth and provide evidence for highly dust-obscured growth phases or episodic, radiatively inefficient accretion rates.

A γ-Ray-emitting Blazar at Redshift 3.64: Fermi-LAT and OVRO Observations of PKS 0201+113

High-redshift (z > 3) γ-ray blazars are rare, but they are crucial for our understanding of jet evolution, γ-ray production and propagation, and the growth of supermassive black holes in the early Universe. A new analysis of Fermi-LAT data reveals a significant (5σ), spectrally soft (Γ ≃ 3.0) γ-ray source in a specific 4 month epoch, cospatial with PKS 0201+113 (z = 3.64). Monitoring of PKS 0201+113 at 15 GHz by the Owens Valley Radio Observatory 40 m telescope from 2008 to 2023 shows a prominent flare that dominates the radio light curve. The maximum of the radio flare coincides with the γ-ray flare, strongly suggesting an association (p-value = 0.023) between the γ-ray and the radio sources. PKS 0201+113 is only the third γ-ray blazar to be identified with z > 3.5, and it is the first such object to be identified by the detection of quasi-simultaneous γ-ray and radio flares. The jet properties of this peculiar blazar have been investigated. A detailed study of a two-zone leptonic model is presented that fits the broadband spectral energy distribution. An alternative scenario is also briefly discussed.

Growth of high redshift supermassive black holes from heavy seeds in the BRAHMA cosmological simulations: Implications of overmassive black holes

Growth of high redshift supermassive black holes from heavy seeds in the <tt>BRAHMA</tt> cosmological simulations: Implications of overmassive black holes

LeMMINGs. Multiwavelength constraints on the co-existence of nuclear star clusters and AGN in nucleated galaxies

ABSTRACT The relation between nuclear star clusters (NSCs) and the growth of the central supermassive black holes (SMBHs), as well as their connection to the properties of the host galaxies, is crucial for understanding the evolution of galaxies. Recent observations have revealed that about 10 per cent of nucleated galaxies host hybrid nuclei, consisting of both NSCs and accreting SMBHs that power active galactic nuclei (AGNs). Motivated by the potential of the recently published multiwavelength data sets from LeMMINGs survey, here we present the most thorough investigation to date of the incidence of hybrid nuclei in a large sample of 100 nearby nucleated galaxies (10 E, 25 S0, 63 S, and 2 Irr), covering a wide range in stellar mass ($M_{*,\rm gal} \sim 10^{8.7}-10^{12}~\rm M_{\odot }$). We identify the nuclei and derive their properties by performing detailed 1D and 2D multicomponent decompositions of the optical and near-infrared HST stellar light distributions of the galaxies using Sérsic and core-Sérsic models. Our AGN diagnostics are based on homogeneously derived nuclear 1.5 GHz e-MERLIN radio, Chandra X-ray (0.3–10 keV), and optical emission-line data. We determine the nucleation fraction ($f_{\rm nuc}$) as the relative incidence of nuclei across the LeMMINGs HST sample and find $f_{\rm nuc} =~$100/149 (= 67 $\pm$ 7 per cent), confirming previous work, with a peak value of $49/56~(= 88 \pm 13$ per cent) at bulge masses $M_{*,\rm bulge}\sim 10^{9.4}- 10^{10.8}~ \rm M_{\odot }$. We identify 30 nucleated LeMMINGs galaxies that are optically active, radio-detected, and X-ray luminous ($L_\textnormal {X} \gt 10^{39}$ erg s$^{-1}$). This indicates that our nucleated sample has a lower limit $\sim$ 30 per cent occupancy of hybrid nuclei, which is a function of $M_{*,\rm bulge}$ and $M_{*,\rm gal}$. We find that hybrid nuclei have a number density of $(1.5 \pm 0.4)\times 10^{-5}$ Mpc$^{-3}$, are more common at $M_{*,\rm gal}\sim 10^{10.6}- 10^{11.8}~\rm M_{\odot }$ and occur, at least, three times more frequently than previously reported.

A two-phase model of galaxy formation: I. The growth of galaxies and supermassive black holes

ABSTRACT We develop a model for galaxy formation and the growth of supermassive black holes (SMBHs), based on the fact that cold dark matter haloes form their gravitational potential wells through a fast phase with rapid change in the potential, and that the high universal baryon fraction makes cooled gas in haloes self-gravitating and turbulent before it can form rotation-supported discs. Gas fragmentation produces subclouds so dense that cloud–cloud collision and drag on clouds are not significant, producing a dynamically hot system of subclouds that form stars and move ballistically to feed the central SMBH. Active galactic nucleus (AGN) and supernova feedback is effective only in the fast phase, and the cumulative effects are to regulate star formation and SMBH growth, as well as to reduce the amount of cold gas in haloes to allow the formation of globally stable discs. Using a set of halo assembly histories, we demonstrate that the model can reproduce a number of observations, including correlations among SMBH mass, stellar mass of galaxies and halo mass, the number densities of galaxies and SMBH, as well as their evolution over the cosmic time.

Fast supermassive black hole growth in the SPT2349--56 protocluster at z=4.3

Large-scale environment is one of the main physical drivers of galaxy evolution. The densest regions at high redshifts (i.e. $z&gt;2$ protoclusters) are gas-rich regions characterised by high star formation activity. The same physical properties that enhance star formation in protoclusters are also thought to boost the growth of supermassive black holes (SMBHs), most likely in heavily obscured conditions. We aim to test this scenario by probing the active galactic nucleus (AGN) content of SPT2349--56:\ a massive, gas-rich, and highly star-forming protocluster core at $z=4.3$ discovered as an overdensity of dusty star-forming galaxies (DSFGs). We compare our results with data on the field environment and other protoclusters We observed SPT2349--56 with Chandra (200 ks) and searched for X-ray emission from the known galaxy members. We also performed a spectral energy distribution fitting procedure to derive the physical properties of the discovered AGNs. In the X-ray band, we detected two protocluster members:\ C1 and C6, corresponding to an AGN fraction among DSFGs in the structure of $ This value is consistent with other protoclusters at $z=2-4$, but higher than the AGN incidence among DSFGs in the field environment. Both AGNs are heavily obscured sources, hosted in star-forming galaxies with $ M_ odot $ stellar masses. We estimate that the intergalactic medium in the host galaxies contributes to a significant fraction (or even entirely) to the nuclear obscuration. In particular, C1 is a highly luminous ($L_X=2 and Compton-thick ($N_H=2 cm^ $) AGN, likely powered by a $M_ BH M_ odot $ SMBH, assuming Eddington-limited accretion. Its high accretion rate suggests that it is in the phase of efficient growth that is generally required to explain the presence of extremely massive SMBHs in the centres of local galaxy clusters. Considering SPT2349--56 and DRC, a similar protocuster at $z=4$, and under different assumptions on their volumes, we find that gas-rich protocluster cores at $z enhance the triggering of luminous (log$ L_X lunit =45-46$) AGNs by three to five orders of magnitude with respect to the predictions from the AGN X-ray luminosity function at a similar redshift in the field environment. We note that this result is not solely driven by the overdensity of the galaxy population in the structures. Our results indicate that gas-rich protoclusters at high redshift boost the growth of SMBHs, which will likely impact the subsequent evolution of the structures. Therefore, they stand as key science targets to obtain a complete understanding of the relation between the environment and galaxy evolution. Dedicated investigations of similar protoclusters are required to definitively confirm this conclusion with a higher statistical significance.

Multiphase Black Hole Feedback and a Bright [C ii] Halo in a LoBAL Quasar at z ∼ 6.6

Although the mass growth of supermassive black holes during the epoch of reionization is expected to play a role in shaping the concurrent growth of their host galaxies, observational evidence of feedback at z ≳ 6 is still sparse. We perform the first multiscale and multiphase characterization of black-hole-driven outflows in the z ∼ 6.6 quasar J0923+0402 and assess how these winds impact the cold gas reservoir. We employ the SimBAL spectral synthesis to fit broad absorption line features and find a powerful ionized outflow on a ≲210 pc scale, with a kinetic power ∼2%–100% of the quasar luminosity. Atacama Large Millimeter/submillimeter Array (ALMA) observations of [C ii] emission allow us to study the morphology and kinematics of the cold gas. We detect high-velocity [C ii] emission, likely associated with a cold neutral outflow at ∼0.5−2 kpc scale in the host galaxy, and a bright extended [C ii] halo with a size of ∼15 kpc. For the first time at such an early epoch, we accurately constrain the outflow energetics in both the ionized and the atomic neutral gas phases. We find such energetics to be consistent with expectations for an efficient feedback mechanism, and both ejective and preventative feedback modes are likely at play. The scales and energetics of the ionized and atomic outflows suggest that they might be associated with different quasar accretion episodes. The results of this work indicate that strong black hole feedback is occurring in quasars at z ≳ 6 and is likely responsible for shaping the properties of the cold gas reservoir up to circumgalactic scales.

From Seeds to Supermassive Black Holes: Capture, Growth, Migration, and Pairing in Dense Protobulge Environments

The origins and mergers of supermassive black holes (SMBHs) remain a mystery. We describe a scenario from a novel multiphysics simulation featuring rapid (≲1 Myr) hyper-Eddington gas capture by a ∼1000 M ⊙ “seed” black hole (BH) up to supermassive (≳106 M ⊙) masses in a massive, dense molecular cloud complex typical of high-redshift starbursts. Due to the high cloud density, stellar feedback is inefficient, and most of the gas turns into stars in star clusters that rapidly merge hierarchically, creating deep potential wells. Relatively low-mass BH seeds at random positions can be “captured” by merging subclusters and migrate to the center in ∼1 freefall time (vastly faster than dynamical friction). This also efficiently produces a paired BH binary with ∼0.1 pc separation. The centrally concentrated stellar density profile (akin to a “protobulge”) allows the cluster as a whole to capture and retain gas and build up a large (parsec-scale) circumbinary accretion disk with gas coherently funneled to the central BH (even when the BH radius of influence is small). The disk is “hypermagnetized” and “flux-frozen”: dominated by a toroidal magnetic field with plasma β ∼ 10−3, with the fields amplified by flux-freezing. This drives hyper-Eddington inflow rates ≳1 M ⊙ yr−1, which also drive the two BHs to nearly equal masses. The late-stage system appears remarkably similar to recently observed high-redshift “little red dots.” This scenario can provide an explanation for rapid SMBH formation, growth, and mergers in high-redshift galaxies.

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

Context. 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. Aims. 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. Methods. 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 log NH &lt; 22), obscured (22 &lt; log NH &lt; 24), and Compton-thick (CTK, log NH &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. Results. 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 high energy X-ray probe (HEX-P): the future of hard X-ray dual AGN science

A fundamental goal of modern-day astrophysics is to understand the connection between supermassive black hole (SMBH) growth and galaxy evolution. Merging galaxies offer one of the most dramatic channels for galaxy evolution known, capable of driving inflows of gas into galactic nuclei, potentially fueling both star formation and central SMBH activity. Dual active galactic nuclei (dual AGNs) in late-stage mergers with nuclear pair separations &lt;10 kpc are thus ideal candidates to study SMBH growth along the merger sequence since they coincide with the most transformative period for galaxies. However, dual AGNs can be extremely difficult to confirm and study. Hard X-ray (&gt;10 keV) studies offer a relatively contamination-free tool for probing the dense obscuring environments predicted to surround the majority of dual AGN in late-stage mergers. To date, only a handful of the brightest and closest systems have been studied at these energies due to the demanding instrumental requirements involved. We demonstrate the unique capabilities of HEX-P to spatially resolve the soft and - for the first time - hard X-ray counterparts of closely-separated (∼2″−5″) dual AGNs in the local Universe. By incorporating physically-motivated obscuration models, we reproduce realistic broadband X-ray spectra expected for deeply embedded accreting SMBHs. Hard X-ray spatially resolved observations of dual AGNs—accessible only to HEX-P—will hence transform our understanding of dual AGN in the nearby Universe.

The evolution of supermassive black hole mass–bulge mass relation by a semi-analytical model, ν2GC

ABSTRACT We have investigated the redshift evolution of the relationship between supermassive black hole (SMBH) mass and host bulge mass using a semi-analytical galaxy formation model ν2GC. Our model reproduces the relation in the local universe well. We find that, at high redshift (z ≳ 3), two sequences appear in the SMBH mass–bulge mass plane. The emergence of these two sequences can be attributed to the primary triggers of the growth of the SMBHs and bulges: galaxy mergers and disc instabilities. The growth of SMBHs and bulges as a result of galaxy mergers is responsible for giving rise to the high-mass sequence, in which SMBHs are more massive for a given host bulge mass than in the low-mas sequence. Conversely, disc instabilities are accountable for the emergence of the low-mass sequence. At lower redshifts, galaxy mergers tend to become increasingly deficient in gas, resulting in a preferential increase of bulge mass without a corresponding growth in SMBH mass. This has the effect of causing galaxies in the upper sequence to shift towards the lower one on the SMBH mass–bulge mass plane. The galaxies that undergo dry mergers serve to bridge the gap between the two sequences, eventually leading to convergence into a single relation known in the local universe. Our results suggest that the observations of the SMBH mass–bulge mass relation in high redshifts can provide insight into their growth mechanisms.

Star Formation and Dust in the Cosmic Web

The large-scale environment of the cosmic web is believed to impact galaxy evolution, but there is still no consensus regarding the mechanisms. We use a semi-analytic model (SAM) galaxy catalog to study the star formation and dust content of local galaxies in different cosmic environments of the cosmic web—namely voids, filaments, walls, and nodes. We find a strong impact of the environment only for galaxies with M stars ≲ 1010.8 M ⊙: the less dense the environment, the larger the star formation rate and dust content at fixed stellar mass. This is attributed to the fact that galaxies in less dense environments typically feature younger stellar populations, a slower evolution of their stellar mass, and delayed star formation compared to galaxies in denser environments. As for galaxies with M stars ≳ 1010.8 M ⊙, the differences among environments are milder, due to the disk-instability-driven supermassive black hole (SMBH) growth implemented in the SAM, which makes SMBH growth, and thus galaxy quenching, environment-insensitive. We qualitatively test our predictions against observations by identifying environments in Sloan Digital Sky Survey Data Release 16 using dust masses derived from the GAMA survey. The agreement is encouraging, particularly at logMstars/M⊙≳10.5–11 , where the specific star formation rates and dust masses appear quite environment-insensitive. This result confirms the importance of in situ growth channels of SMBHs.

Overmassive Black Holes at Cosmic Noon: Linking the Local and the High-redshift Universe

We report for the first time a sample of 12 supermassive black holes (SMBHs) hosted by low-mass galaxies at cosmic noon, i.e., in a redshift range consistent with the peak of star formation history: z ∼ 1–3. These black holes are 2 orders of magnitude too massive for the stellar content of their hosts when compared with the local relation for active galaxies. These overmassive systems at cosmic noon share similar properties with the high-z sources found ubiquitously in recent James Webb Space Telescope (JWST) surveys (same range of black-hole-to-stellar-mass ratio, bolometric luminosity, and Eddington ratio). We argue that black hole feedback processes, for which there is possible evidence in five of the sources, and the differing environments in galactic nuclei at these respective epochs play a key role in these overmassive systems. These findings contribute to our understanding of the growth and coevolution of SMBHs and their host galaxies across cosmic time, offering a link between the early Universe (z > 4) observed by JWST and observations of the present-day Universe (z ≲ 1).

A spectacular galactic scale magnetohydrodynamic powered wind in ESO 320-G030

How galaxies regulate nuclear growth through gas accretion by supermassive black holes (SMBHs) is one of the most fundamental questions in galaxy evolution. One potential way to regulate nuclear growth is through a galactic wind that removes gas from the nucleus. It is unclear whether galactic winds are powered by jets, mechanical winds, radiation, or via magnetohydrodynamic (MHD) processes. Compact obscured nuclei represent a significant phase of galactic nuclear growth. These galaxies hide growing SMBHs or unusual starbursts in their very opaque, extremely compact (r &lt; 100 pc) centres. They are found in approximately 30% of the luminous and ultra-luminous infrared galaxy population. Here, we present high-resolution ALMA observations (∼30 mas, ∼5 pc) of ground-state and vibrationally excited HCN towards ESO 320-G030 (IRAS 11506-3851). ESO 320-G030 is an isolated luminous infrared galaxy known to host a compact obscured nucleus and a kiloparsec-scale molecular wind. Our analysis of these high-resolution observations excludes the possibility of a starburst-driven wind, a mechanically or energy driven active galactic nucleus wind, and exposes a molecular MDH wind. These results imply that the nuclear evolution of galaxies and the growth of SMBHs are similar to the growth of hot cores or protostars where gravitational collapse of the nuclear torus drives a MHD wind. These results mean galaxies are capable, in part, of regulating the evolution of their nuclei without feedback.

Mapping the Growth of Supermassive Black Holes as a Function of Galaxy Stellar Mass and Redshift

The growth of supermassive black holes is strongly linked to their galaxies. It has been shown that the population mean black hole accretion rate ( BHAR¯ ) primarily correlates with the galaxy stellar mass (M ⋆) and redshift for the general galaxy population. This work aims to provide the best measurements of BHAR¯ as a function of M ⋆ and redshift over ranges of 109.5 < M ⋆ < 1012 M ⊙ and z < 4. We compile an unprecedentedly large sample with 8000 active galactic nuclei (AGNs) and 1.3 million normal galaxies from nine high-quality survey fields following a wedding cake design. We further develop a semiparametric Bayesian method that can reasonably estimate BHAR¯ and the corresponding uncertainties, even for sparsely populated regions in the parameter space. BHAR¯ is constrained by X-ray surveys sampling the AGN accretion power and UV-to-infrared multiwavelength surveys sampling the galaxy population. Our results can independently predict the X-ray luminosity function (XLF) from the galaxy stellar mass function (SMF), and the prediction is consistent with the observed XLF. We also try adding external constraints from the observed SMF and XLF. We further measure BHAR¯ for star-forming and quiescent galaxies and show that star-forming BHAR¯ is generally larger than or at least comparable to the quiescent BHAR¯ .

The high energy X-ray probe (HEX-P): constraining supermassive black hole growth with population spin measurements

Constraining the primary growth channel of supermassive black holes (SMBHs) remains one the most actively debated questions in the context of cosmological structure formation. Owing to the expected connection between SMBH spin parameter evolution and the accretion and merger history of individual black holes, population spin measurements offer a rare observational window into the cosmic growth of SMBHs. As of today, the most common method for estimating SMBH spin relies on modeling the relativistically broaden atomic profiles in the reflection spectrum observed in X-rays. In this paper, we study the observational requirements needed to confidently distinguish between the primary SMBH growth channels based on their distinct spin-mass distributions predicted by the Horizon-AGN cosmological simulation. Indoing so, we characterize outstanding limitations associated with the existing measurements and discuss the landscape of future observational campaigns which could be planned and executed with future X-ray observatories. We focus our attention on the High-Energy X-ray Probe (HEX-P), a proposed probe-class mission designed to serve the high-energy community in the 2030s.

Spectroscopic Confirmation of Obscured AGN Populations from Unsupervised Machine Learning

We present the result of a spectroscopic campaign targeting active galactic nucleus (AGN) candidates selected using a novel unsupervised machine-learning (ML) algorithm trained on optical and mid-infrared photometry. AGN candidates are chosen without incorporating prior AGN selection criteria and are fainter, redder, and more numerous, ∼340 AGN deg−2, than comparable photometric and spectroscopic samples. In this work, we obtain 178 rest-optical spectra from two candidate ML-identified AGN classes with the Hectospec spectrograph on the MMT Observatory. We find that our first ML-identified group is dominated by Type I AGNs (85%) with a <3% contamination rate from non-AGNs. Our second ML-identified group is mostly comprised of Type II AGNs (65%), with a moderate contamination rate of 15% primarily from star-forming galaxies. Our spectroscopic analyses suggest that the classes recover more obscured AGNs, confirming that ML techniques are effective at recovering large populations of AGNs at high levels of extinction. We demonstrate the efficacy of pairing existing WISE data with large-area and deep optical/near-infrared photometric surveys to select large populations of AGNs and recover obscured growth of supermassive black holes. This approach is well suited to upcoming photometric surveys, such as Euclid, Rubin, and Roman.