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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 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 Binary supermassive black holes (SMBHs) are consequences of galaxy mergers and dominate the low-frequency gravitational-wave background. Finding binary SMBHs in existing time-domain observations has proven difficult, as their periodic, electromagnetic signals can be confused with the natural variability of single quasars. In this work, we investigate the effects of host-galaxy contamination and survey design (cadence and duration) on the detectability of binary SMBHs with the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST). We simulate millions of LSST light curves of single and binary quasars, with a distribution of quasar and host-galaxy properties motivated by empirical observations and the anticipated LSST detection space. We then apply simple sinusoidal curve fits as a potential computationally inexpensive detection method. We find that host-galaxy contamination will increase false-positive rates and decrease binary parameter recovery rates. Lower-mass, lower-luminosity binary systems are most likely to be negatively affected by host-galaxy contamination. We also find that monitoring duration affects binary detection more than survey effective cadence for this detection method. As the light-curve duration increases, false-positive rates are suppressed and binary parameter recovery rates, especially for binary periods, are improved. Increasing the light-curve duration from 5 to 10 yr shows the most dramatic improvement for successful binary detection and false-positive rejection, with additional improvement from extending the light-curve duration to 20 yr. The observation duration increase is especially critical for recovering binary periods that are longer than a decade. 

Abstract Ultrafast outflows (UFOs) are powerful, highly ionized winds launched from the innermost regions of active galactic nuclei (AGNs), reaching velocities of 0.03–0.3cand playing a key role in AGN feedback. We present a photoionization analysis of an 18 ks XMM-Newton snapshot of the Seyfert 1 AGN Mrk 877, revealing three distinct UFO components with line-of-sight velocities of $0.10_{-0.005}^{+0.005}c$ , $0.04_{-0.004}^{+0.005}c$ , and $0.05_{-0.004}^{+0.005}c$ . These components span a broad range of ionization parameters and column densities, producing absorption features across both soft and hard X-ray bands. Even under the most conservative assumption for the volume filling factor, the fastest component exceeds 5% of the Eddington luminosity, making it capable of driving strong galaxy-scale feedback. The soft X-ray UFO component, despite its lower ionization, shares a similar velocity as a higher-ionization component, hinting at a two-phase medium likely shaped by clumpiness or interactions with ambient material. The density profile inferred from the absorption measurement distributions and the positive trend between outflow momentum rate and radiation momentum flux suggest that wind is powered by a combination of radiative and magnetic driving. 

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 SDSS J1539+3954 (z ≈ 1.935), a radio-quiet weak-line quasar (WLQ), exhibited exceptional X-ray variability in 2019–2020, with its X-ray flux increasing by over 20 times from 2013 to 2019 and subsequently dropping by at least a factor of 9 in 2020. Motivated by the empirical correlations between X-ray and radio emission in the cores of active galactic nuclei (AGNs), we carried out a follow-up radio study in the 0.3–10 GHz range using the Giant Metrewave Radio Telescope (GMRT; 2020, 2022, 2024) and Very Large Array (VLA; 2022), and analyzed archival Very Large Array Sky Survey (VLASS) 3 GHz data (2017–2023) to investigate the source’s radio properties and potential connection with the X-ray behavior. Our observations reveal a compact radio source with a spectral index of −0.65 ± 0.15 in the frequency range 0.3–1.4 GHz and −1.09 ± 0.16 in 3–10 GHz. While the source was undetected in VLA-FIRST (1994) and VLASS epochs, the GMRT and VLA observations show no statistically significant variability over the monitored period. The absence of detectable changes in the radio flux, despite strong X-ray variability, suggests no direct connection between the X-ray variability and the radio emission, consistent with the thick-disk-plus-outflow (TDO) model for WLQs. However, the sensitivity limit of the surveys prevents us from drawing definitive conclusions regarding variability on longer timescales between the VLA-FIRST and GMRT epochs. We further explore possible mechanisms driving the radio emission from this source. Our analysis rules out small-scale jets and coronal emission as the primary drivers of the radio emission, suggesting that extended emission from AGN winds and star formation is the more plausible mechanism. 

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 report the fastest quasar outflow first detected in the ultraviolet, via variable Civand Siivabsorption at outflow velocities −77,000 km s⁻¹to at least −90,000 km s⁻¹, in the radio-quiet quasar SDSS J231854.31+243954.2 (J2318). J2318 is a weak-lined quasar in the rest-frame ultraviolet, but Gemini GNIRS spectroscopy reveals an Hαredshift ofz = 2.6781 ± 0.0004. A 20 yr photometric time series shows peak-to-peak variability of 0.5 mag in thegband. The Civoutflow strengthened monotonically over three epochs spanning ∼2.2 rest-frame years. The existence of such a high-velocity outflow implies that models of quasar outflows must be able to either accelerate gas to 0.3cwhile still preserving Civand Siivions, or enable the formation of Civand Siivions in gas, which has been accelerated to 0.3c. Virial estimates reveal a black-hole mass of 1.65 × 10⁹M_⊙, which leads to an Eddington luminosity and Eddington ratio of 2.4 × 10⁴⁷erg s⁻¹and 0.45, respectively. Using very conservative assumptions, the UV-absorbing outflow alone has an estimated mass loss of >0.82M_⊙yr⁻¹and a kinetic luminosity ratioL_kin/L_bol≥ 0.75%. The lower limit is just above the threshold usually cited for significant feedback on the host galaxy. Comparison to PDS 456, the only other known quasar with a UV-absorbing outflow at 0.3c, suggests that the true $\dot{M}$ andL_kin/L_bolcould be up to 2 orders of magnitude larger. 

Abstract We present Chandra observations of 63 sources from the Gemini Near Infrared Spectrograph−Distant Quasar Survey, of which 54 were targeted by snapshot observations in Cycle 24. A total of 55 sources are clearly detected in at least one X-ray band, and we set stringent upper limits on the X-ray fluxes of the remaining eight sources. In combination with rest-frame ultraviolet–optical spectroscopic data for these sources, we assess whether X-rays can provide a robust accretion rate indicator for quasars, particularly at the highest accessible redshifts. We utilize a recently modified Hβ-based Eddington luminosity ratio estimator, as well as the Civλ1549 emission-line parameter space, to investigate trends and correlations with the optical–X-ray spectral slope (α_ox) and the effective hard X-ray power-law photon index (Γ). We find thatα_oxdoes not improve current accretion rate estimates based on Hβor Civ. Instead, within the limitations of our sample, we confirm previous findings that the Civparameter space may be a better indicator of the accretion rate up toz ∼ 3.5. We also find that the average Γ values for a small subset of our sources, as well as the average Γ value in different groupings of our sources, are consistent with their respective relatively high Eddington luminosity ratios. Deeper X-ray observations of our X-ray-detected sources are needed for measuring Γ accurately and testing whether this parameter can serve as a robust, unbiased accretion rate diagnostic. 

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.