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Abstract Dust-obscured galaxies (DOGs) with extremely red optical-to-infrared colors are often associated with intense starburst and active galactic nucleus (AGN) activity. Studying DOGs can provide insights into the processes that drive the growth of galaxies and their central supermassive black holes. However, the general DOG population is heterogeneous, spanning a wide range of evolutionary stages, and has X-ray obscuring column densities (N_H) covering low to high levels. In this work, we focus on seven high Eddington ratio DOGs ( $\log {\lambda }_{\mathrm{Edd}}\gtrsim -0.5$) to examine their X-ray obscuration properties using new and archival X-ray observations. We confirm that these systems are generally heavily obscured, with six out of seven havingN_H ≳ 10²³cm⁻²and three out of seven havingN_H ≳ 10²⁴cm⁻². Based on the observed similarity with the rare Hot DOG population, we argue that both high-λ_EddDOGs and Hot DOGs likely trace the postmerger phase, during which AGNs are enshrouded by large columns of dust-rich material. 

Abstract We present a systematic investigation of extremely X-ray variable active galactic nuclei (AGNs) in the ≈5.3 deg²XMM-SERVS XMM-LSS region. Eight variable AGNs are identified with rest-frame 2 keV flux density variability amplitudes around 6–12. We comprehensively analyze the X-ray and multiwavelength data to probe the origin of their extreme X-ray variability. It is found that their extreme X-ray variability can be ascribed to changing accretion state or changing obscuration from dust-free absorbers. For five AGNs, their X-ray variability is attributed to changing accretion state, supported by contemporaneous multiwavelength variability and the absence of X-ray absorption in the low-state spectra. With new Multiple Mirror Telescope (MMT) spectra for four of these sources, we confirm one changing-look AGN. One MMT AGN lacks multiepoch spectroscopic observations, while the other two AGNs do not exhibit changing-look behavior, likely because the MMT observations did not capture their high states. The X-ray variability of the other three AGNs is explained by changing obscuration, and they show only mild long-term optical/IR variability. The absorbers of these sources are likely clumpy accretion-disk winds, with variable column densities and covering factors along the lines of sight. 

The black hole occupation fraction (focc) defines the fraction of galaxies that harbor central massive black holes (MBHs), irrespective of their accretion activity level. While it is widely accepted that focc is nearly 100% in local massive galaxies with stellar masses M⋆ ≳ 1010 M⊙, it is not yet clear whether MBHs are ubiquitous in less-massive galaxies. In this work, we present new constraints on focc based on over 20 yr of Chandra imaging data for 1606 galaxies within 50 Mpc. We employ a Bayesian model to simultaneously constrain focc and the specific accretion-rate distribution function, p(λ), where the specific accretion rate is defined as λ = LX/M⋆, where LX is the MBH accretion luminosity in the 2─10 keV range. Notably, we find that p(λ) peaks around 1028ergs−1M⊙−1 ; above this value, p(λ) decreases with increasing λ, following a power law that smoothly connects with the probability distribution of bona fide active galactic nuclei. We also find that the occupation fraction decreases dramatically with decreasing M⋆: in high-mass galaxies (M⋆ ≍ 1011−12 M⊙), the occupation fraction is >93% (a 2σ lower limit), and then declines to 66%−7%+8% (1σ errors) between M⋆ ≍ 109−10 M⊙, and to 33%−9%+13% in the dwarf galaxy regime between M⋆ ≍ 108−9 M⊙. Our results have significant implications for the normalization of the MBH mass function over the mass range most relevant for tidal disruption events, extreme mass ratio inspirals, and MBH merger rates that upcoming facilities are poised to explore. 

Abstract The coevolution of supermassive black holes and their host galaxies represents a fundamental question in astrophysics. One approach to investigating this question involves comparing the star formation rates (SFRs) of active galactic nuclei (AGNs) with those of typical star-forming galaxies. At relatively low redshifts (z≲ 1), radio AGNs manifest diminished SFRs, indicating suppressed star formation, but their behavior at higher redshifts is unclear. To examine this, we leveraged galaxy and radio-AGN data from the well-characterized W-CDF-S, ELAIS-S1, and XMM-LSS fields. We established two mass-complete reference star-forming galaxy samples and two radio-AGN samples, consisting of 1763 and 6766 radio AGNs, the former being higher in purity and the latter more complete. We subsequently computed star-forming fractions (f_SF; the fraction of star-forming galaxies to all galaxies) for galaxies and radio-AGN host galaxies and conducted a robust comparison between them up toz≈ 3. We found that the tendency for radio AGNs to reside in massive galaxies primarily accounts for their lowf_SF, which also shows a strong negative dependence uponM_⋆and a strong positive evolution withz. To investigate further the star formation characteristics of those star-forming radio AGNs, we constructed the star-forming main sequence (MS) and investigated the behavior of the position of AGNs relative to the MS atz≈ 0–3. Our results reveal that radio AGNs display lower SFRs than star-forming galaxies in the low-zand high-M_⋆regime and, conversely, exhibit comparable or higher SFRs than MS star-forming galaxies at higher redshifts or lowerM_⋆. 

Abstract Tidal disruption events (TDEs) could be an important growth channel for massive black holes in dwarf galaxies. Theoretical work suggests that the observed active galactic nuclei (AGNs) in dwarf galaxies are predominantly TDE-powered. To assess this claim, we perform variability analyses on the dwarf-hosted AGNs detected in the 7 Ms Chandra Deep Field-South survey, with observations spanning ≈16 yr. Based on the spectral energy distribution modeling withx-cigale, we select AGNs hosted by dwarf galaxies (stellar mass below 10¹⁰M_⊙). We focus on X-ray sources with full-band detections, leading to a sample of 78 AGNs (0.122 ≤z≤ 3.515). We fit the X-ray light curves with a canonical TDE model oft^−5/3and a constant model. If the former outperforms the latter in fitting quality for a source, we consider the source as a potential TDE. We identify five potential TDEs, constituting a small fraction of our sample. Using true- and false-positive rates obtained from fitting models to simulated light curves, we perform Bayesian analysis to obtain the posterior of the TDE fraction for our sample. The posterior peaks close to zero (2.56%), and we obtain a 2σupper limit of 9.80%. Therefore, our result indicates that the observed AGNs in dwarf galaxies are not predominantly powered by TDEs. 

Abstract Multiyear observations from the Sloan Digital Sky Survey (SDSS) Reverberation Mapping ​(RM) project have significantly increased the number of quasars with reliable RM lag measurements. We statistically analyze target properties, light-curve characteristics, and survey design choices to identify factors crucial for successful and efficient RM surveys. Analyzing 172 high-confidence (“gold”) lag measurements from SDSS-RM for the Hβ, Mgii, and Civemission lines, we find that the Durbin–Watson statistic (a statistical test for residual correlation) is the most significant predictor of light curves suitable for lag detection. The variability signal-to-noise ratio and emission-line placement on the detector also correlate with successful lag measurements. We further investigate the impact of the observing cadence on the survey design by analyzing the effect of reducing observations in the first year of SDSS-RM. Our results demonstrate that a modest reduction in the observing cadence to ∼1.5 weeks between observations can retain approximately 90% of the lag measurements compared to twice-weekly observations in the initial year. Provided similar and uniform sampling in subsequent years, this adjustment has a minimal effect on the overall recovery of lags across all emission lines. These results provide valuable inputs for optimizing future RM surveys. 

Abstract 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 measuredM_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 fromz= 4 toz= 1 and remains largely unchanged fromz= 1 toz= 0. The overall SMBH growth is generally dominated by the accretion channel, with possible exceptions at high mass (M_BH≳ 10⁸M_⊙orM_⋆≳ 10¹¹M_⊙) 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 withM_⋆. 

Abstract Over three decades of reverberation mapping (RM) studies on local broad-line active galactic nuclei (AGNs) have measured reliable black hole (BH) masses for >100 AGNs. These RM measurements reveal a significant correlation between the Balmer broad-line region (BLR) size and AGN optical luminosity (theR–Lrelation). Recent RM studies for AGN samples with more diverse BH parameters (e.g., mass and Eddington ratio) reveal a substantial intrinsic dispersion around the averageR–Lrelation, suggesting that variations in the broadband spectrum, driven by accretion parameters and other factors such as the cloud distribution and inclination, significantly influence the measuredR–Lrelation. Here we perform a detailed photoionization investigation of expected broad-line properties as functions of accretion parameters using AGN continuum models fromqsosed. We compare theoretical predictions with observations of a sample of 67z ≲ 0.5 reverberation-mapped AGNs with rest-frame optical and UV spectra in the moderate-accretion regime (Eddington ratioλ_Edd ≡ L/L_Edd < 0.5). The UV/optical line strengths and their dependences on accretion parameters are reasonably well reproduced by the locally optimally emitting cloud photoionization models. We provide quantitative recipes using optical/UV line flux ratios to infer the unobservable ionizing continuum. Additionally, photoionization models with universal values of ionization parameter ( $\log U_{\mathrm{H}}=-2$) and hydrogen density ( $\log n\left(\mathrm{H}\right)=12$) can qualitatively reproduce the observed globalR–Lrelation for the current RM AGN sample. However, such models fail to reproduce the observed decrease in BLR size with increasingL/L_Eddat fixed optical luminosity, implying that gas density or BLR structure may systematically change with accretion rate. 

Abstract We present dynamical modeling of the broad-line region (BLR) of the highly variable active galactic nucleus (AGN) SDSS J141041.25+531849.0 (z= 0.359) using photometric and spectroscopic monitoring data from the Sloan Digital Sky Survey (SDSS) Reverberation Mapping project and the current fifth-generation SDSS Black Hole Mapper program, spanning from early 2013 to early 2023. We model the geometry and kinematics of the BLR in the Hβ, Hα, and Mgiiemission lines for three different time periods to measure the potential change of structure within the BLR across time and line species. We find a moderately face-on $(i_{\mathrm{full}-\mathrm{state}}=29.{68}_{-3.62}^{+4.74}\mathrm{deg})$thick-disk $({\theta }_{\mathrm{opn},\mathrm{full}-\mathrm{state}}=42.{04}_{-3.96}^{+4.32}\mathrm{deg})$geometry for most BLRs, with a joint estimate for the mass of the supermassive black hole for each of three time periods, yielding ${\log }_{10}(M_{\mathrm{BH}}/M_{\odot })=8.10_{-0.03}^{+0.03}$when using the full data set. The inferred individual virial factorf∼ 1.6 is moderately smaller than the average factor for a local sample of dynamically modeled AGNs. There is strong evidence for nonvirial motion, with over 70% of clouds on inflowing/outflowing orbits. We analyze the change in model parameters across emission lines, finding the radii of BLRs for the emission lines are consistent with the following relative sizesR_Hβ ≲ R_MgII ≲ R_Hα. Comparing results across time, we findR_low-state ≲ R_high-state, with the change in BLR size for Hβbeing more significant than for the other two lines. The data also reveal complex, time-evolving, and potentially transient dynamics of the BLR gas over a decade-long timescale, encouraging for future dynamical modeling of fine-scale BLR kinematics. 

Aims.The goal of this project is to construct an estimator for the masses of supermassive black holes in active galactic nuclei (AGNs) based on the broad Hαemission line. Methods.We made use of published reverberation mapping data. We remeasured all Hαtime lags from the original data as we find that reverberation measurements are often improved by detrending the light curves. Results.We produced mass estimators that require only the Hαluminosity and the width of the Hαemission line as characterized by either the full width at half maximum or the line dispersion. Conclusions.It is possible, on the basis of a single spectrum covering the Hαemission line, to estimate the mass of the central supermassive black hole in AGNs with all three parameters believed to affect mass measurement – luminosity, line width, and Eddington ratio – taken into account. The typical formal accuracy in such estimates is of order 0.2–0.3 dex relative to the reverberation-based masses.