Search for: All records

Abstract We report a detailed analysis of GAMA 376183, a powerful, heavily obscured active galactic nucleus (AGN) hosted by a low-mass galaxy (M_⋆ ≈ 10¹⁰M_⊙) likely experiencing a galaxy merger. The source was initially identified due to its remarkably strong [Nev]λ3426 emission, exhibiting a rest-frame equivalent width of ≈48 Å. We present ∼100 ks Nuclear Spectroscopic Telescope Array (or NuSTAR) follow-up observations, confirming its heavily obscured nature with a column density (in cm⁻²) of $\log N_{\mathrm{H}}=23.3_{-1.2}^{+0.4}$ and an intrinsic 2–10 keV luminosity (in erg s⁻¹) of $\log L_{\mathrm{X},\mathrm{int}}=42.92_{-0.20}^{+0.24}$ . GAMA 376183 thus represents one of the few known heavily obscured AGNs in low-mass galaxies. Its estimated Eddington ratio isλ_Edd ≈ 0.8, indicative of rapid black hole growth. High-resolution optical images reveal a disturbed, likely merging morphology, while its multiwavelength spectral energy distribution indicates a recent starburst in its host galaxy. These pieces of evidence suggest that the ongoing merger has triggered both the heavily obscured, Eddington-limited accretion and the starburst, making GAMA 376183 a rare observed case in low-mass galaxies. Overall, this unique source demonstrates that (i) [Nev] can help identify heavily obscured low-mass AGNs, and (ii) the merger-driven coevolution framework established for massive galaxies may also extend to low-mass galaxies. 

Abstract It is well established that cosmic supermassive black hole (SMBH) growth peaks atz ≈ 1.5–2, followed by a strong decline of ≈1–1.5 dex toward the present day, with the comoving number density of higher-luminosity active galactic nuclei (AGNs) peaking at higher redshift (referred to as “AGN downsizing”). We leverage the best current measurements of the SMBH accretion distribution, based upon data from nine well-characterized extragalactic fields with a “wedding-cake” design, to investigate and quantify the drivers of the drastic decline in cosmic SMBH growth. The decline in the typical Eddington ratio (λ_Edd) of AGNs (decreasing by ≈1.35 dex fromz ≈ 1.5–2 toz ≈ 0.2) is the dominant driver for the broad decline in SMBH growth, rather than a shift of accretion activity to less-massive SMBHs. Asλ_Edddecreases toward lower redshift, the primary contributor to the cosmic SMBH accretion density (ρ_BHAR) has shifted from high-λ_EddAGNs to low-λ_EddAGNs, even though the latter always dominate the comoving AGN number density atz < 4. We also find that the decline in SMBH growth toward lower SMBH mass in less-massive galaxies is primarily due to the decreasing outburst luminosity rather than the duty cycle. 

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. 

Abstract We present photometric selection of type 1 quasars in the ≈5.3 deg²XMM-Large Scale Structure survey field with machine learning. We constructed our training and blind-test samples using spectroscopically identified Sloan Digital Sky Survey quasars, galaxies, and stars. We utilized the XGBoost machine learning method to select a total of 1591 quasars. We assessed the classification performance based on the blind-test sample, and the outcome was favorable, demonstrating high reliability (≈99.9%) and good completeness (≈87.5%). We used XGBoost to estimate photometric redshifts of our selected quasars. The estimated photometric redshifts span a range from 0.41 to 3.75. The outlier fraction of these photometric redshift estimates is ≈17%, and the normalized median absolute deviation (σ_NMAD) is ≈0.07. To study the quasar disk–corona connection, we constructed a subsample of 1016 quasars with Hyper Suprime-Cami < 22.5 after excluding radio-loud and potentially X-ray-absorbed quasars. The relation between the optical-to-X-ray power-law slope parameter (α_OX) and the 2500 Å monochromatic luminosity (L_2500Å) for this subsample is ${\alpha }_{\mathrm{OX}}=(-0.156\pm 0.007)\log L_{2500\AA }+(3.175\pm 0.211)$ with a dispersion of 0.159. We found this correlation in good agreement with the correlations in previous studies. We explored several factors, which may bias theα_OX–L_2500Årelation, and found that their effects are not significant. We discussed possible evolution of theα_OX–L_2500Årelation with respect toL_2500Åor redshift. 

Context. To explain the well-known tension between cosmological parameter constraints obtained from the primary cosmic microwave background (CMB) and those drawn from X-ray-selected galaxy cluster samples identified with early data, we propose a possible explanation for the incompleteness of detected clusters being higher than estimated. Specifically, we suggest that certain types of galaxy groups or clusters may have been overlooked in previous works. Aims. We aim to search for galaxy groups and clusters with especially extended surface brightness distributions by creating a new X-ray-selected catalog of extended galaxy clusters from the XMM-SpitzerExtragalactic Representative Volume Survey (XMM-SERVS) data, based on a dedicated source detection and characterization algorithm optimized for extended sources. Methods. Our state-of-the-art algorithm is composed of wavelet filtering, source detection, and characterization. We carried out a visual inspection of the optical image, and spatial distribution of galaxies within the same redshift layer to confirm the existence of clusters and estimated the cluster redshift with the spectroscopic and photometric redshifts of galaxies. The growth curve analysis was used to characterize the detections. Results. We present a catalog of extended X-ray galaxy clusters detected from the XMM-SERVS data. The XMM-SERVS X-ray eXtended Galaxy Cluster (XVXGC) catalog features 141 cluster candidates. Specifically, there are 53 clusters previously identified as clusters with intracluster medium (ICM) emission (class 3); 40 that were previously known as optical or infrared (IR) clusters, but detected as X-ray clusters for the first time (class 2); and 48 identified as clusters for the first time (class 1). Compared with the class 3 sample, the “class 1 + class 2” sample is systematically fainter and exhibits a flatter surface brightness profile. Specifically, the median flux in [0.5–2.0] keV band for “class 1 + class 2” and class 3 sample is 1.288 × 10⁻¹⁴erg/s/cm²and 1.887 × 10⁻¹⁴erg/s/cm², respectively. The median values ofβ(i.e., the slope of the cluster surface brightness profile) are 0.506 and 0.573 for the “class 1 + class 2” and class 3 samples, respectively. The entire sample is available at the CDS. 

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 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 Dust-obscured galaxies (DOGs) are enshrouded by dust and many are believed to host accreting supermassive black holes (SMBHs), which makes them unique objects for probing the coevolution of galaxies and SMBHs. We select and characterize DOGs in the 13 deg²XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS), leveraging the superb multiwavelength data—from X-rays to radio. We select 3738 DOGs atz≈ 1.6–2.1 in XMM-SERVS, while maintaining good data quality without introducing significant bias. This represents the largest DOG sample with thorough multiwavelength source characterization. Spectral energy distribution modeling shows DOGs are a heterogeneous population consisting of both normal galaxies and active galactic nuclei (AGNs). Our DOGs are massive ( $\log M_{\star }/M_{☉}\approx 10.7-11.3$ ), 174 are detected in X-rays, and they are generally radio-quiet systems. X-ray detected DOGs are luminous and are moderately to heavily obscured in X-rays. Stacking analyses for the X-ray undetected DOGs show highly significant average detections. Critically, we compare DOGs with matched galaxy populations. DOGs have similar AGN fractions compared with typical galaxy populations. X-ray detected DOGs have higherM_⋆and higher X-ray obscuration, but they are not more star-forming than typical X-ray AGNs. Our results potentially challenge the relevance of the merger-driven galaxy-SMBH coevolution framework for X-ray detected DOGs.