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1. Testing the Evolution of the Correlations between Supermassive Black Holes and their Host Galaxies using Eight Strongly Lensed Quasars

   Ding, Xuheng; Treu, Tommaso; Birrer, Simon; Agnello, Adriano; Sluse, Dominique; Fassnacht, Chris; Auger, Matthew W.; Wong, Kenneth C.; Suyu, Sherry H.; Morishita, Takahiro; et al (April 2020, Monthly notices of the Royal Astronomical Society)

   One of the main challenges in using high redshift active galactic nuclei to study the correlations between the mass of the supermassive Black Hole (MBH) and the properties of their active host galaxies is instrumental resolution. Strong lensing magnification effectively increases instrumental resolution and thus helps to address this challenge. In this work, we study eight strongly lensed active galactic nuclei (AGN) with deep Hubble Space Telescope imaging, using the lens modelling code Lenstronomy to reconstruct the image of the source. Using the reconstructed brightness of the host galaxy, we infer the host galaxy stellar mass based on stellar population models. MBH are estimated from broad emission lines using standard methods. Our results are in good agreement with recent work based on non-lensed AGN, providing additional evidence that the correlation evolves over cosmic time. At the moment, the sample size of lensed AGN is small and thus they provide mostly a consistency check on systematic errors related to resolution for the non-lensed AGN. However, the number of known lensed AGN is expected to increase dramatically in the next few years, through dedicated searches in ground and space based wide field surveys, and they may become a key diagnostic of black hole and galaxy co-evolution. 

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2. DAVOS: Dwarf Active Galactic Nuclei from Variability for the Origins of Seeds: Properties of Variability-selected Active Galactic Nuclei in the COSMOS Field and Expectations for the Rubin Observatory

   https://doi.org/10.3847/1538-4357/ad54ca  

   Burke, Colin J; Liu, Yichen; Ward, Charlotte A; Liu, Xin; Natarajan, Priyamvada; Greene, Jenny E (August 2024, The Astrophysical Journal)

   Abstract We study the black hole mass–host galaxy stellar mass relation,M_BH–M_*, of a sample ofz< 4 optically variable active galactic nuclei (AGNs) in the COSMOS field. The parent sample of 491 COSMOS AGNs were identified by optical variability from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) program. Using publicly available catalogs and spectra, we consolidate their spectroscopic redshifts and estimate virial black hole masses using broad-line widths and luminosities. We show that variability searches with deep, high-precision photometry like the HSC-SSP can identity AGNs in low-mass galaxies up toz∼ 1. However, their black holes are more massive given their host galaxy stellar masses than predicted by the local relation for active galaxies. We report thatz∼ 0.5–4 variability-selected AGNs are meanwhile more consistent with theM_BH–M_*relation for local inactive early-type galaxies. This result is in agreement with most previous studies of theM_BH–M_*relation at similar redshifts and indicates that AGNs selected from variability are not intrinsically different from the broad-line Type 1 AGN population at similar luminosities. Our results demonstrate the need for robust black hole and stellar mass estimates for intermediate-mass black hole candidates in low-mass galaxies at similar redshifts to anchor this scaling relation. Assuming that these results do not reflect a selection bias, they appear to be consistent with self-regulated feedback models wherein the central black hole and stars in galaxies grow in tandem. 

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3. The Host Galaxies of Active Galactic Nuclei with Direct Black Hole Mass Measurements*

   https://doi.org/10.3847/1538-4357/ae41ad  

   Bennert, Vardha N; Winkel, Nico; Treu, Tommaso; Ding, Xuheng; U, Vivian; Remigio, Raymond P; Barth, Aaron J; Malkan, Matthew A; Villafaña, Lizvette; Allen, Samantha; et al (March 2026, The Astrophysical Journal)

   Abstract Reverberation mapping (RM) determines the mass of black holes (BHs) in active galactic nuclei (AGNs) by resolving the BH gravitational sphere of influence in the time domain. Recent RM campaigns have yielded direct BH masses through dynamical modeling for a sample of 32 objects, spanning a wide range of AGN luminosities and BH masses. In addition, accurate BH masses have been determined by spatially resolving the broad-line region with GRAVITY for a handful of AGNs. Here, we present a detailed analysis of Hubble Space Telescope images using surface-brightness profile fitting with state-of-the-art programs. We derive AGN luminosity and host-galaxy properties, such as radii and luminosities for the spheroid, disk, and bar (if present). The spheroid effective radii are used to measure stellar velocity dispersion from integral-field spectroscopy. Since the BH masses of our sample do not depend on any assumption of the virial factor needed in single-epoch spectroscopic mass estimates, we can show that the resulting scaling relations between the mass of the supermassive BHs and their host galaxies match those of quiescent galaxies, naturally extending to lower masses in these (predominantly) spiral galaxies. We find that the inner AGN orientation, as traced by the broad-line region inclination angle, is uncorrelated with the host-galaxy disk. Our sample has the most direct and accurateM_BH measurements of any AGN sample and provides a fundamental local benchmark for studies of the evolution of massive BHs and their host galaxies across cosmic time. 

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4. Dwarf Active Galactic Nuclei from Variability for the Origins of Seeds (DAVOS): Properties of Variability-selected AGN in the Dark Energy Survey Deep Fields

   https://doi.org/10.3847/1538-4357/ae0e64  

   Liu, Yichen; Burke, Colin J; Miura, Diego; Liu, Xin; Yang, Qian; Natarajan, Priyamvada; Ward, Charlotte A (November 2025, The Astrophysical Journal)

   Abstract We study the black hole mass–host galaxy stellar mass relation,M_BH–M_*, for a sample of 706z ≲ 1.5 andi ≲ 24 optically variable active galactic nuclei (AGNs) in three Dark Energy Survey (DES) Deep Fields: C3, X3, E2, which partially cover Chandra Deep Field-South, XMM Large Scale Structure survey, and European Large Area ISO Survey, respectively. The parent sample was identified by optical variability from the DES supernova survey program imaging. Using publicly available spectra and photometric catalogs, we consolidate their spectroscopic redshifts, estimate their black hole masses using broad line widths and luminosities, and obtain improved stellar masses using spectral energy distribution fitting from X-ray to mid-infrared wavelengths. Our results confirm previous work from Hyper-Suprime Camera imaging that variability searches with deep, high-precision photometry can reliably identify AGNs in low-mass galaxies up toz ∼ 1. However, we find that the hosted black holes are more massive than predicted by the local AGN relation, fixing host galaxy stellar mass. Instead,z ∼ 0.1–1.5 variability-selected AGNs lie in between theM_BH–M_*relation for local inactive early-type galaxies and local active galaxies. This result agrees with most previous studies of theM_BH–M_*relation for AGNs at similar redshifts, regardless of the selection technique. We demonstrate that studies of variability-selected AGN provide critical insights into the low-mass end of theM_BH–M_*relation, shedding light on the occupation fraction of that provides constraints on early black hole seeding mechanisms and self-regulated feedback processes during their growth and coevolution with their hosts. 

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5. Changing-look Active Galactic Nuclei in SDSS-V: Host-galaxy Properties and Black Hole Scaling Relations

   https://doi.org/10.3847/1538-4357/ae5495  

   Zeltyn, Grisha; Trakhtenbrot, Benny; Eracleous, Michael; Anderson, Scott F; Ricci, Claudio; Merloni, Andrea; Runnoe, Jessie; Krumpe, Mirko; Aird, James; Assef, Roberto J; et al (April 2026, The Astrophysical Journal)

   Abstract Changing-look active galactic nuclei (CL-AGNs) exhibit dramatic spectral variability on unexpectedly short timescales, challenging standard accretion flow models. Despite growing samples, the physical drivers of this extreme variability, and the potential link to host-galaxy properties, remain unknown. Regardless of the underlying mechanism, the transition between AGN-dominated and host-dominated spectra offers a unique opportunity to study relations between AGNs and their hosts within the same objects. We present intermediate-resolution spectroscopy of 23 CL-AGNs identified by the Sloan Digital Sky Survey V (SDSS-V), obtained with the Very Large Telescope/X-shooter and Gemini-N/GMOS. An analysis of the Mgiiλ2798 emission line observed in the spectra demonstrates that the majority of these sources cannot be driven by variable obscuration. Our CL-AGNs roughly follow theM_BH–σ_*andM_BH–M_*relations of inactive galaxies, with a median black hole-to-stellar mass ratio of 0.38 %. We find no evidence that the stellar population properties of our CL-AGNs, including stellar mass, age, young stellar fraction, and star formation rate, differ from those of type 2 AGNs in SDSS. These results suggest that CL-AGNs reside in typical AGN host galaxies and that their extreme variability is likely unrelated to host-galaxy environment, supporting the idea that CL-AGNs are not a distinct population, but rather represent a phase of normal AGN activity. This result, in turn, implies that CL-AGNs can serve as useful probes of the AGN-host connection, providing access to both AGN-dominated and host-dominated spectra of the same systems. 

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