Meredith C. Powell

Quasars acting as strong gravitational lenses offer a rare opportunity to probe the redshift evolution of scaling relations between supermassive black holes and their host galaxies, particularly the M _BH – M _host relation. Using these powerful probes, the mass of the host galaxy can be precisely inferred from the Einstein radius θ _E . Using 812,118 quasars from DESI DR1 (0.03 ≤ z ≤ 1.8), we searched for quasars lensing higher-redshift galaxies by identifying background emission-line features in their spectra. To detect these rare systems, we trained a convolutional neural network (CNN) on mock lenses constructed from real DESI spectra of quasars and emission-line galaxies (ELGs), achieving a high classification performance (AUC = 0.99). We also trained a regression network to estimate the redshift of the background ELG. Applying this pipeline, we identified seven high-quality (Grade A) lens candidates, each exhibiting a strong [O II ] doublet at a higher redshift than the foreground quasar; four candidates additionally show H β , [O III ] λ 4959, and [O III ] λ 5007 emission. These results significantly expand the sample of quasar lens candidates beyond the 12 identified and 3 confirmed in previous work and demonstrate the potential for scalable, data-driven discovery of quasars as strong lenses in upcoming spectroscopic surveys.

The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is a wide-field, integral-field spectroscopic survey designed to map the large-scale distribution of Ly α -emitting galaxies (LAEs) at 1.88 < z < 3.52 and constrain dark energy at cosmic noon. Using the 10 m Hobby–Eberly Telescope and the Visible Integral-Field Replicable Unit (IFU) Spectrograph, HETDEX obtains >35,000 spectra per exposure over 3500–5500 Å at R ∼ 800 with ∼ 1 . ″ 8 image quality, enabling an untargeted census of emission-line galaxies across 540 deg ² . We present HETDEX Public Data Release 1 (PDR1), comprising 431,713 IFU observations covering 86.67 deg ² of noncontiguous sky in the Spring (13 ^h , +51°) and Fall (1 . h 5, 0°) fields, along with legacy regions (Cosmic Evolution Survey, Great Observations Origins Deep Survey North, North Ecliptic Pole, SA22). PDR1 includes the HETDEX Public Source Catalog 2 (HPSC2), an expanded and reprocessed version of E. Mentuch Cooper et al. (2023) incorporating four additional years of data, improved quality control, and new machine learning classifiers. HPSC2 contains 426,654 LAEs, 491,411 [O II ] emitters, 19,457 low- z galaxies, 18,303 active galactic nuclei, and 150,608 stars, providing coordinates, redshifts or stellar velocities, and 1D spectra for each source. Because the data cubes use local sky subtraction optimized for faint emission-line detection, they are not suited for absolute surface-brightness measurements or very extended nearby galaxies. Appendix materials include the full detection catalog, the 1.6 million–candidate LAE sample, and raw detection databases. All products are publicly accessible through the HETDEX data portal ( https://hetdex.org/data-results/ ), including access to a public JupyterLab . HPSC2 is also publicly available via Zenodo (doi: 10.5281/zenodo.19581262 ).

X-ray variability is a well-established characteristic of active galactic nuclei (AGNs) known to correlate inversely with both the supermassive black hole mass ( M _BH ) and luminosity, although the degree of each remains a topic of debate. The potential of X-ray variability as a proxy for M _BH or for intrinsic L _X has led to proposals to use AGNs as standard candles to test cosmological models. However, the large intrinsic dispersion in these relations has limited their practical applications. In this work, we investigate the dependence of X-ray variability on physical properties of AGNs using a sample of 134 Seyfert 1 galaxies from the BAT AGN Spectroscopic Survey (BASS), which is the largest sample to date (it is more than three times larger than samples used in previous studies). Contrary to earlier findings, we observed that X-ray variability correlates with luminosity just as strongly as with M _BH . Furthermore, we still find no evidence of the expected anti-correlation between variability and the Eddington ratio, even when using refined bolometric luminosities from Spectral Energy Distribution (SED) fitting to compute the Eddington ratio. From a cosmological perspective, the increased sample size reduces the scatter in the log L –log σ _NXS ² relation to ∼0.63 dex – a significant improvement over previous results, but still too large to serve as competitive standard candles, when compared to Supernovae Ia (uncertainties on distances of ∼5–10%) or the L _X − L _UV relation in quasars (uncertainties of 10–12%). We tested including the width of broad emission lines as additional parameters, but we found that this does not significantly lower the observed dispersion, contrary to previous studies on smaller samples. Finally, we discuss how future X-ray missions such as AXIS and NewAthena will improve this scenario by enabling precise variability measurements for thousands of AGNs up to redshift z ∼ 3.

We present the first statistical census of emission-line variable active galactic nuclei (EVA) at cosmic noon by combining untargeted and deep Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) spectroscopy with multiepoch spectra from the Sloan Digital Sky Survey, DESI, and LAMOST. Anchoring all candidates to a HETDEX spectroscopic epoch and requiring an active galactic nucleus (AGN) classification in either the HETDEX or external epoch(s), we identify a homogeneous sample of 100 EVA at z ∼ 1.5, including 98 that are newly identified. Emission-line variability is selected primarily through statistically significant line-flux changes, supplemented by extensive visual inspections using contemporaneous photometric light curves. The resulting incidence fraction is f _EVA ∼ 0.9%. The rest-frame intervals between spectroscopic epochs span ∼1–10 yr, with brightening and dimming events exhibiting statistically indistinguishable characteristic timescales (Δ T ∼ 2.2 and ∼2.6 yr, respectively). A key result is the characterization of the Baldwin effect in the time domain: while many EVA follow the ensemble Baldwin effect (eBeff) between two epochs, a substantial fraction exhibit apparent anti-eBeff responses. Time-resolved spectroscopy of an individual source reveals that the intrinsic equivalent width–luminosity relation is nonstationary, with the line-to-continuum responsivity systematically evolving from stronger to weaker across successive variability cycles; sparse two-epoch sampling of this evolving intrinsic Baldwin evolution naturally produces both eBeff-like and anti-eBeff behaviors. Finally, EVA show no strong preference for extreme Eddington ratios but exhibit a mild tendency toward lower λ _Edd values relative to matched control samples, driven primarily by sources observed in their dim states. Together, these results establish a coherent framework for interpreting emission-line variability in AGN at the peak epoch of cosmic black hole growth.

Identifying active galactic nuclei (AGNs) using only one wavelength region may miss AGNs with characteristics unfavorable for the identification method, which introduces bias in the sample. To better understand these selection effects, we compare the multiwavelength properties of 2584 X-ray- and IR-selected AGNs at z < 3 in the COSMOS field. The X-ray-selected sample consists of the 2219 AGNs with intrinsic 0.5–10 keV X-ray luminosity greater than 10 ⁴³ erg s ⁻¹ ; the 993 IR-selected AGNs are identified by their high-contrast, power-law IR colors using Spitzer/IRAC observations. We find that both selection methods miss a significant fraction of AGNs, as only 24.3% of AGNs (628 out of the total of 2584 AGNs) are recovered by both selection criteria. X-ray selection can capture the most diverse range of multiwavelength spectral emission features, while IRAC selection is biased against AGNs with a steeply decreasing power flux ( λF _λ ) between 1 and 6 μ m. For AGNs with X-ray detections, IRAC-selected sources are 2.5× more X-ray luminous than AGNs not identified by their IR colors. IRAC-selected AGNs without detectable X-rays are obscured, as they have a mean X-ray correction factor log ( L X , obs / L X , int ) = −1.4; 28.5%–42.2% of these AGNs are Compton-thick (according to estimated column densities). Only 1.4% of X-ray-selected AGNs are Compton-thick. The AGN selection technique used significantly impacts the overall characteristics of the resulting AGN sample.

A fraction of active galactic nuclei (AGN) have double-peaked Hα, Hβ, and Mg II broad lines attributed to emission from rotating gas in the accretion disk. Using optical spectroscopy of a flux-limited sample of AGN selected via ultrahard X-rays from the BAT AGN Spectroscopic Survey (BASS), we systematically identify 71 double-peaked emitters (DPEs) among 343 broad-line AGN with redshifts 0.004 < z < 0.297 and X-ray luminosities of 40 < log L 2 − 10 KeV (erg s⁻¹) < 45.7, and provide their best-fit accretion disk parameters. We find that ∼21% of X-ray-selected broad-line AGN are DPEs, consistent with rates previously reported for z < 0.2 broad-line AGN selected for strong optical variability in the Zwicky Transient Facility. 11 of 71 DPEs (15%) exhibited a single-peaked Gaussian component to the broad line profile in addition to the double-peaked disk profile. In this sample, DPEs have intrinsically higher masses by ∼0.4 dex and lower Eddington ratios by ∼0.3 dex than other broad-line AGN, and have a preference for elliptical host galaxies, higher X-ray luminosities, and higher [O i] λ6302 to narrow Hα flux ratios than other broad-line AGN. We find that DPEs are not segregated from non-DPE broad-line AGN in the L _bol versus M _BH relation or their X-ray to radio luminosity ratios, and do not show a preference for intermediate Seyfert types over Seyfert 1s. We do not find differences in a wide range of multiwavelength properties when comparing DPEs to non-DPE broad-line AGN, including optical and mid-IR variability levels, Wide-field Infrared Survey Explorer colors, α _ox, the column density of neutral obscuring material N _H, and the rate of changing-look events. We discuss the two populations in the context of multicomponent disk-wind models of the AGN broad-line region and consider how unrecognized contributions of disk emission to the broad lines may introduce biases in “virial” supermassive black hole mass estimates, with consequences for the inferred M _BH–M _* relation.

Context. The large-scale environments of active galactic nuclei (AGNs) reveal important information on the growth and evolution of supermassive black holes (SMBHs). Previous AGN clustering measurements using two-point correlation functions have hinted that AGNs with massive black holes preferentially reside in denser cosmic regions than AGNs with less massive SMBHs. At the same time, little to no dependence on the accretion rate has been found; however, the significance of such trends has been limited. Aims. Here, we present k th-nearest-neighbor ( k NN) statistics of 2MASS galaxies around AGNs from the Swift/BAT AGN Spectroscopic survey. These statistics have been shown to contribute additional higher order clustering information on the cosmic density field. Methods. By calculating the distances to the nearest seven galaxy neighbors in angular separation to each AGN within two redshift ranges (0.01 < z < 0.03 and 0.03 < z < 0.06), we compared their cumulative distribution functions to that of a randomly distributed sample to demonstrate the sensitivity of this method to the clustering of AGNs. We also split the AGNs into bins of bolometric luminosity, black hole mass, and Eddington ratio (while controlling for redshift) to search for trends between k NN statistics and fundamental AGN properties. Results. We find that AGNs with massive SMBHs have significantly closer neighbors than AGNs with less massive SMBHs (at the 99.98% confidence level), especially in our lower redshift range. We find less significant trends with luminosity or Eddington ratio. By comparing our results to empirical SMBH-galaxy-halo models implemented in N-body simulations, we show that small-scale k NN trends with black hole mass may go beyond stellar mass dependencies. Conclusions. This suggests that massive SMBHs in the local universe reside in more massive dark matter halos and denser regions of the cosmic web, which may indicate that environment is important for the growth of SMBHs, bolstering prior conclusions based on correlation functions.

Active galactic nuclei (AGN) emit radiation via accretion across the entire energy spectrum. While the standard disk and corona model can somewhat describe this emission, it fails to predict specific features such as the soft X-ray excess, the short-term optical/UV variability, and the observed UV/X-ray correlation in AGN. In this context, the fraction of AGN emission in different bands (i.e., bolometric corrections) can be useful to better understand the accretion physics of AGN. Past studies have shown that the X-ray bolometric corrections are strongly dependent on the physical properties of AGN, such as their luminosities and Eddington ratios. However, since these two parameters depend on each other, it has been unclear which is the main driver of the X-ray bolometric corrections. We present here results from a large study of hard-X-ray-selected (14–195 keV) nearby (z < 0.1) AGN. Based on our systematic analysis of the simultaneous optical-to-X-ray spectral energy distributions of 236 unobscured AGN, we found that the primary parameter controlling the X-ray bolometric corrections is the Eddington ratio. Our results show that, while the X-ray bolometric correction increases with the bolometric luminosity for sources with intermediate Eddington ratios (0.01–1), this dependence vanishes for sources with lower Eddington ratios (<0.01). This could be used as evidence for a change in the accretion physics of AGN at low Eddington ratios.

We investigate the high-ionization, narrow [Ne V] λ3427 line emission in a sample of over 340 ultrahard X-ray (14–195 keV) selected active galactic nuclei (AGN) drawn from the BAT AGN Spectroscopic Survey project. The analysis includes measurements in individual and stacked spectra and considers several key AGN properties such as X-ray luminosity, supermassive black hole (SMBH) mass, Eddington ratios, and line-of-sight column density. The [Ne V] λ3427 line is robustly detected in ≈43% (146/341) of the AGN in our sample, with no significant trends between the detection rate and key AGN/SMBH properties. In particular, the detection rate remains high even at the highest levels of obscuration (>70% for log N H / cm − 2 ) ≳ 23 ). On the other hand, even some of our highest signal-to-noise spectra (S/N > 50) lack a robust [Ne v] detection. The typical (median) scaling ratios between [Ne v] line emission and (ultra)hard X-ray emission in our sample are log L [ Ne V ] / L 14 − 150 keV ≃ − 3.75 and log L [ Ne V ] / L 2 − 10 keV ≃ − 3.36 . The scatter on these scaling ratios, ≲0.5 dex, is comparable to, and indeed smaller than, what is found for other commonly used tracers of AGN radiative outputs (e.g., [O III] λ5007). Otherwise, we find no significant relations between the (relative) strength of [Ne v] and the basic AGN/SMBH properties under study, in contrast with simple expectations from models of SMBH accretion flows. Our results reaffirm the usability of [Ne v] as an AGN tracer even in highly obscured systems, including dual AGN and high-redshift sources.