Kavli Affiliate: Linhua Jiang
| First 5 Authors: Wei-Jian Guo, Hu Zou, Victoria Anne Fawcett, Rebecca Canning, Stephanie Juneau
| Summary:
Changing-look Active Galactic Nuclei (CL AGN) can be generally confirmed by
the emergence (turn-on) or disappearance (turn-off) of broad emission lines,
associated with a transient timescale (about $100sim5000$ days) that is much
shorter than predicted by traditional accretion disk models. We carry out a
systematic CL AGN search by cross-matching the spectra coming from the Dark
Energy Spectroscopic Instrument and the Sloan Digital Sky Survey. Following
previous studies, we identify CL AGN based on $rm{H}alpha $, $rm{H}beta$,
and Mg,{sc ii} at $zleq0.75$ and Mg,{sc ii}, C,{sc iii}], and C,{sc
iv} at $z>0.75$. We present 130 CL AGN based on visual inspection and three
selection criteria, including 2 $rm{H}alpha$, 45 $rm{H}beta$, 38 Mg,{sc
ii}, 61 C,{sc iii}], and 10 C,{sc iv} CL AGN. Twenty cases show
simultaneous appearances/disappearances of two broad emission lines while three
AGN exhibit the concurrent appearance of three broad emission lines. We also
present 91 CL AGN candidates with significant flux variation of broad emission
lines but remaining strong broad components. In the confirmed CL AGN, 42 cases
show additional CL candidate features for different lines. In this paper, we
find 1) a 95:35 ratio of a turn-on to turn-off CL AGN; 2) the highest redshift
CL AGN ($z=3.56$) ever discovered; 3) an upper limit transition timescale
ranging from 244 to 5762 days in the rest-frame; 4) the majority of CL AGN
follow the bluer-when-brighter trend. Our results greatly increase the current
CL census ($30sim50%$) and would be conducive to explore the underlying
physical mechanism.
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