2024/01/03 by Grisha Zeltyn, Benny Trakhtenbrot, Michael Eracleous +41 · 1 voice · 9 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #astro-ph.GA #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/ad2f30
arxiv published 2024/01/03 · openalex publication_date 2024/04/26 · openalex created_date 2024/04/27 · arxiv updated 2024/05/01 · openalex updated_date 2026/07/30
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 a f Edd distribution that significantly differs from that of a carefully constructed, redshift- and luminosity-matched control sample (Anderson–Darling test yielding p AD ≈ 6 × 10 −5 ; median f Edd ≈ 0.025 versus 0.043). This preference for low f Edd strengthens previous findings of higher CL-AGN incidence at lower f Edd , found in smaller samples. Finally, we show that the broad Mg ii emission line in our CL-AGN sample tends to vary significantly less than the broad H β emission 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.