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Abstract Supermassive black holes (SMBHs) are found in the centers of massive galaxies, and galaxy mergers should eventually lead to SMBH mergers. Quasar activity has long been associated with galaxy mergers, so here we investigate if supermassive black hole binaries (SMBHBs) are preferentially found in quasars. Our multimessenger investigation folds together a gravitational-wave background signal from NANOGrav, a sample of periodic active galactic nucleus candidates from the Catalina Real-Time Transient Survey, and a quasar mass function, to estimate an upper limit on the fraction of quasars which could host an SMBHB. We find at 95% confidence that quasars are at most 5 times as likely to host an SMBHB as a random galaxy. Pulsar timing arrays may therefore be more likely to find SMBHBs by prioritizing quasars over a random selection of galaxies in their searches. 

We use JWST Near-Infrared Spectrograph observations from the Cosmic Evolution Early Release survey, GLASS-JWST ERS (GLASS), and JWST Advanced Deep Extragalactic Survey to measure rest-frame optical emission-line ratios of 89 galaxies atz > 4. The stacked spectra of galaxies with and without a broad-line feature reveal a difference in the [Oiii]λ4364 and Hγratios. This motivated our investigation of the [Oiii]λ4364/Hγversus [Neiii]/[Oii] diagram. We define two active galactic nucleus (AGN)/star formation (SF) classification lines based on 21,048 Sloan Digital Sky Survey galaxies atz ∼ 0. After applying a redshift correction to the AGN/SF lines, we find 69.2% of broad-line active galactic nuclei (BLAGN) continue to land in the AGN region of the diagnostic, largely due to the [Neiii]/[Oii] ratio. However, 33.0% of non-BLAGN land is in the AGN region as well. The [Oiii]λ4364/Hγversus [Neiii]/[Oii] diagram does not robustly separate BLAGN from non-broad-line galaxies atz> 4. This could be due to star-forming galaxies having harder ionization, or these galaxies contain a narrow line AGN, which are not accounted for. We further inspected galaxies without broad emission lines in each region of [Oiii]λ4364/Hγversus [Neiii]/[Oii] diagram and found that they have slightly stronger Ciii]λ1908 fluxes and equivalent width when landing in the BLAGN region. However, the cause of this higher ionization is unclear and may be revealed by observing UV lines. 

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 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. 

JWST spectroscopy has discovered a population ofz ≳ 3.5 galaxies with broad Balmer emission lines and narrow forbidden lines that are consistent with hosting active galactic nuclei (AGN). Many of these systems, now known as “little red dots,” are compact and have unique colors that are very red in the optical/near-infrared and blue in the ultraviolet. The relative contribution of galaxy starlight and AGN to these systems remains uncertain, especially for the galaxies with unusual blue+red spectral energy distributions. In this work, we use Balmer decrements to measure the independent dust attenuation of the broad and narrow emission-line components of a sample of 29 broad-line AGN identified from three public JWST spectroscopy surveys: CEERS, JADES, and RUBIES. Stacking the narrow components from the spectra of 25 sources with broad Hαand no broad Hβresults in a median narrow Hα/Hβ= $2.47_{-0.05}^{+0.05}$(consistent withA_v = 0) and broad Hα/Hβ>8.85 (A_v > 3.63). The narrow and broad Balmer decrements imply little to no attenuation of the narrow emission lines, which are consistent with being powered by star formation and located on larger physical scales. Meanwhile, the lower limit in the broad Hα/Hβdecrement, with broad Hβundetected in the stacked spectrum of 25 broad HαAGN, implies significant dust attenuation of the broad-line emitting region that is presumably associated with the central AGN. Our results indicate that these systems, on average, are consistent with heavily dust-attenuated AGN powering the red parts of their SED, while their blue UV emission is powered by unattenuated star formation in the host galaxy. 

Abstract Periodic signatures in time-domain observations of quasars have been used to search for binary supermassive black holes (SMBHs). These searches, across existing time-domain surveys, have produced several hundred candidates. The general stochastic variability of quasars, however, can masquerade as a false-positive periodic signal, especially when monitoring cadence and duration are limited. In this work, we predict the detectability of binary SMBHs in the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST). We apply computationally inexpensive sinusoidal curve fits to millions of simulated LSST Deep Drilling Field light curves of both single, isolated quasars and binary quasars. The period and phase of simulated binary signals can generally be disentangled from quasar variability. Binary amplitude is overestimated and poorly recovered for two-thirds of potential binaries due to quasar accretion variability. Quasars with strong intrinsic variability can obscure a binary signal too much for recovery. We also find that the most luminous quasars mimic current binary candidate light curves and their properties: The false-positive rates are 60% for these quasars. The reliable recovery of binary period and phase for a wide range of input binary LSST light curves is promising for multi-messenger characterization of binary SMBHs. However, pure electromagnetic detections of binaries using photometric periodicity with amplitude greater than 0.1 mag will result in samples that are overwhelmed by false positives. This paper represents an important and computationally inexpensive way forward for understanding the true and false-positive rates for binary candidates identified by Rubin. 

Abstract We explore reprocessing models for a sample of 17 hypervariable quasars, taken from the Sloan Digital Sky Survey Reverberation Mapping project, which all show coordinated optical luminosity hypervariability with amplitudes of factors ≳2 between 2014 and 2020. We develop and apply reprocessing models for quasar light curves in simple geometries that are likely to be representative of quasar inner environments. In addition to the commonly investigated thin-disk model, we include the thick-disk and hemisphere geometries. The thick-disk geometry could, for instance, represent a magnetically elevated disk, whereas the hemisphere model can be interpreted as a first-order approximation for any optically thick out-of-plane material caused by outflows/winds, warped/tilted disks, and so on. Of the 17 quasars in our sample, 11 are best-fitted by a hemisphere geometry, five are classified as thick disks, and both models fail for just one object. We highlight the successes and shortcomings of our thermal reprocessing models in case studies of four quasars that are representative of the sample. While reprocessing is unlikely to explain all of the variability that we observe in quasars, we present our classification scheme as a starting point for revealing the likely geometries of reprocessing for quasars in our sample and hypervariable quasars in general. 

ABSTRACT Supermassive black hole binaries (SMBHBs) are a natural outcome of galaxy mergers and should form frequently in galactic nuclei. Sub-parsec binaries can be identified from their bright electromagnetic emission, e.g. Active Galactic Nuclei (AGNs) with Doppler shifted broad emission lines or AGN with periodic variability, as well as from the emission of strong gravitational radiation. The most massive binaries (with total mass >108M⊙) emit in the nanohertz band and are targeted by Pulsar Timing Arrays (PTAs). Here we examine the synergy between electromagnetic and gravitational wave signatures of SMBHBs. We connect both signals to the orbital dynamics of the binary and examine the common link between them, laying the foundation for joint multimessenger observations. We find that periodic variability arising from relativistic Doppler boost is the most promising electromagnetic signature to connect with GWs. We delineate the parameter space (binary total mass/chirp mass versus binary period/GW frequency) for which joint observations are feasible. Currently multimessenger detections are possible only for the most massive and nearby galaxies, limited by the sensitivity of PTAs. However, we demonstrate that as PTAs collect more data in the upcoming years, the overlapping parameter space is expected to expand significantly. 

Abstract “Changing-look” active galactic nuclei (CL-AGNs) challenge our basic ideas about the physics of accretion flows and circumnuclear gas around supermassive black holes. Using first-year Sloan Digital Sky Survey V (SDSS-V) repeated spectroscopy of nearly 29,000 previously known active galactic nuclei (AGNs), combined with dedicated follow-up spectroscopy, and publicly available optical light curves, we have identified 116 CL-AGNs where (at least) one broad emission line has essentially (dis-)appeared, as well as 88 other extremely variable systems. Our CL-AGN sample, with 107 newly identified cases, is the largest reported to date, and includes ∼0.4% of the AGNs reobserved in first-year SDSS-V operations. Among our CL-AGNs, 67% exhibit dimming while 33% exhibit brightening. Our sample probes extreme AGN spectral variability on months to decades timescales, including some cases of recurring transitions on surprisingly short timescales (≲2 months in the rest frame). We find that CL events are preferentially found in lower-Eddington-ratio (f_Edd) systems: Our CL-AGNs have af_Edddistribution that significantly differs from that of a carefully constructed, redshift- and luminosity-matched control sample (Anderson–Darling test yieldingp_AD≈ 6 × 10⁻⁵; medianf_Edd≈ 0.025 versus 0.043). This preference for lowf_Eddstrengthens previous findings of higher CL-AGN incidence at lowerf_Edd, found in smaller samples. Finally, we show that the broad Mgiiemission line in our CL-AGN sample tends to vary significantly less than the broad Hβemission line. Our large CL-AGN sample demonstrates the advantages and challenges in using multi-epoch spectroscopy from large surveys to study extreme AGN variability and physics. 

Abstract We explore the possibility and practical limitations of using a three-line approach to measure both the slope and normalization of the dust attenuation law in individual galaxies. To do this, we focus on a sample of 11 galaxies with existing ground-based Balmer Hαand Hβmeasurements from slit spectra, plus space-based grism constraints on Paschen-β. When accounting for observational uncertainties, we show that one galaxy has a well-constrained dust-law slope and normalization in the range expected from theoretical arguments; this galaxy therefore provides an example of what may be possible in the future. However, most of the galaxies are best fit by unusually steep or shallow slopes. We then explore whether additional astrophysical effects or observational biases could explain the elevated Paschen-β/Hαratios driving these results. We find that galaxies with high Paschen-β/Hαratios may be explained by slightly sub-unity covering fractions (>97%). Alternatively, differing slit losses for different lines can have a large impact on the results, emphasizing the importance of measuring all three lines with a consistent spectroscopic aperture. We conclude that, while the three-line approach to constraining the shape of the dust attenuation law in individual galaxies is promising, deep observations and a consistent observational strategy will be required to minimize observational biases and to disentangle the astrophysically interesting effect of differing covering fractions. The James Webb Space Telescope will provide more sensitive measurements of Balmer and Paschen lines for galaxies atz≈ 0.3–2, enabling uniform constraints on the optical–infrared dust attenuation law and its intrinsic variation.