Identifying Changing-look AGNs Using Variability Characteristics

doi:10.3847/1538-4357/ad3049

Identifying Changing-look AGNs Using Variability Characteristics

2024-04-30

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DOI：10.3847/1538-4357/ad3049

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Changing-look (CL) active galactic nuclei (AGNs), characterized by the 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 versus 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 and Type 2 AGNs can be neatly separated on the basis of the variability metric sigma QSO, which quantifies the resemblance of a light curve to a damped random walk model. For a small subsample, 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, representing a high success rate for our method. Our results suggest that the occurrence rate of CL AGNs is similar to 0.3% over timescales of 5-20 yr, and confirm that the CL transition typically occurs at an Eddington ratio of less than or similar to 0.01.

Keywords:

DIGITAL-SKY-SURVEY

ACTIVE GALACTIC NUCLEI

REVERBERATION MAPPING PROJECT

SURVEY QUASAR PROPERTIES

BROAD-LINE REGION

OPTICAL VARIABILITY

BLACK-HOLES

EMISSION

SAMPLE

GALAXY

Identifying Changing-look AGNs Using Variability Characteristics

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