Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. II. Statistical Properties from the First Data Release
arxiv(2024)
Abstract
We present the identification of changing-look active galactic nuclei
(CL-AGNs) from the Dark Energy Spectroscopic Instrument First Data Release and
Sloan Digital Sky Survey Data Release 16 at z ≤0.9. To confirm the CL-AGNs,
we utilize spectral flux calibration assessment via an [O iii]-based
calibration, pseudo-photometry examination, and visual inspection. This
rigorous selection process allows us to compile a statistical catalog of 561
CL-AGNs, encompassing 527 Hβ, 149Hα, and 129 Mg II CL
behaviors. In this sample, we find 1) a 283:278 ratio of turn-on to turn-off
CL-AGNs. 2) the critical value for CL events is confirmed around Eddington
ratio ∼0.01. 3) a strong correlation between the change in the luminosity
of the broad emission lines (BEL) and variation in the continuum luminosity,
with Mg II and Hβ displaying similar responses during CL phases. 4)
the Baldwin-Phillips-Terlevich diagram for CL-AGNs shows no statistically
difference from the general AGN catalog. 5) five CL-AGNs are associated with
asymmetrical mid-infrared flares, possibly linked to tidal disruption events.
Given the large CL-AGNs and the stochastic sampling of spectra, we propose that
some CL events are inherently due to typical AGN variability during low
accretion rates, particularly for CL events of the singular BEL. Finally, we
introduce a Peculiar CL phase, characterized by a gradual decline over decades
in the light curve and the complete disappearance of entire BEL in faint
spectra, indicative of a real transition in the accretion disk.
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