2024/02/28 by Shu Wang, Wang, Shu, Jong-Hak Woo +17 · 7 citations
Engineering · Psychology · #Astrophysics of Galaxies (astro-ph.GA) #Color perception and design #FOS: Physical sciences #Industrial Technology and Control Systems
paper · pdf · doi:10.48550/arxiv.2402.18131
openalex publication_date 2024/02/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Changing-look (CL) Active Galactic Nuclei (AGNs), characterized by appearance/disappearance of broad emission lines in the span of a few years, present a challenge for the AGN unified model, whereby the Type 1 vs. Type 2 dichotomy results from orientation effects alone. We present a systematic study of a large sample of spectroscopically classified AGNs, using optical variability data from the Zwicky Transient Facility (ZTF) as well as follow-up spectroscopy data. We demonstrate that Type 1 vs. 2 AGN can be neatly separated on the basis of the variability metric σ\rm QSO, which quantifies the resemblance of a light curve to a damp random walk model. For a small sub-sample, however, the ZTF light curves are inconsistent with their previous classification, suggesting the occurrence of a CL event. Specifically, we identify 35 (12) turn-on (turn-off) CL AGN candidates at z < 0.35. Based on follow-up spectroscopy, we confirm 17 (4) turn-on (turn-off) CL AGNs out of 21 (5) candidates, presenting a high success rate of our method. Our results suggest that the occurrence rate of CL AGNs is ∼0.3% over timescales of 5 to 20 years, and confirm that the CL transition typically occurs at the Eddington ratio of ≤ 0.01.