High-redshift Extreme Variability Quasars from Sloan Digital Sky Survey Multi-Epoch Spectroscopy. (arXiv:2006.08645v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Guo_H/0/1/0/all/0/1">Hengxiao Guo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Peng_J/0/1/0/all/0/1">Jiacheng Peng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_K/0/1/0/all/0/1">Kaiwen Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burke_C/0/1/0/all/0/1">Colin J. Burke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_X/0/1/0/all/0/1">Xin Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sun_M/0/1/0/all/0/1">Mouyuan Sun</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_S/0/1/0/all/0/1">Shu Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kong_M/0/1/0/all/0/1">Minzhi Kong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sheng_Z/0/1/0/all/0/1">Zhenfeng Sheng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_T/0/1/0/all/0/1">Tinggui Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+He_Z/0/1/0/all/0/1">Zhicheng He</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gu_M/0/1/0/all/0/1">Minfeng Gu</a>
We perform a systematic search for high-redshift ($z >$ 1.5) extreme
variability quasars (EVQs) using repeat spectra from the Sixteenth Data Release
of Sloan Digital Sky Survey, which provides a baseline spanning up to $sim$18
yrs in the observed frame. We compile a sample of 348 EVQs with a maximum
continuum variability at rest frame 1450 Angstrom of more than 100% (i.e.,
$delta$V $equiv$ (Max$-$Min)/Mean $>$1). Among those EVQs, we discover 23 new
Changing-Look Active Galactic Nuclei (CLAGNs) with CL behaviors in different UV
lines, e.g., CIV, CIII], SiIV, and MgII. Importantly, spurious CLAGNs caused by
SDSS problematic spectral flux calibration, e.g., fiber drop issue, are
rejected. Compared with normal EVQs, we find that CLAGNs have systematically
lower continuum luminosity and broader emission line widths, hence lower
Eddington ratios. Statistical tests of EVQ/CLAGN properties suggest that CLAGNs
are likely to be a subset of EVQs with less efficient accretion rather than a
distinctive AGN population. Moreover, we find that the difference composite
spectra (i.e., bright$-$faint) of EVQs and CLAGNs are both similar to those of
normal quasars with a power-law slope of $alpha_{rm lambda,diff}sim-2$,
further supporting that they belong to the same population with analogous
intrinsic variability mechanisms, e.g., rapid accretion rate change with a
possible state transition. Finally, we also confirm the anti-breathing of CIV
(i.e., line width increases as luminosity increases) in EVQs, and find that in
addition to $sim$ 0.4 dex systematic uncertainty in single-epoch CIV virial
black hole mass estimates, an extra scatter of $sim$ 0.3 dex will be
introduced by extreme variability.
We perform a systematic search for high-redshift ($z >$ 1.5) extreme
variability quasars (EVQs) using repeat spectra from the Sixteenth Data Release
of Sloan Digital Sky Survey, which provides a baseline spanning up to $sim$18
yrs in the observed frame. We compile a sample of 348 EVQs with a maximum
continuum variability at rest frame 1450 Angstrom of more than 100% (i.e.,
$delta$V $equiv$ (Max$-$Min)/Mean $>$1). Among those EVQs, we discover 23 new
Changing-Look Active Galactic Nuclei (CLAGNs) with CL behaviors in different UV
lines, e.g., CIV, CIII], SiIV, and MgII. Importantly, spurious CLAGNs caused by
SDSS problematic spectral flux calibration, e.g., fiber drop issue, are
rejected. Compared with normal EVQs, we find that CLAGNs have systematically
lower continuum luminosity and broader emission line widths, hence lower
Eddington ratios. Statistical tests of EVQ/CLAGN properties suggest that CLAGNs
are likely to be a subset of EVQs with less efficient accretion rather than a
distinctive AGN population. Moreover, we find that the difference composite
spectra (i.e., bright$-$faint) of EVQs and CLAGNs are both similar to those of
normal quasars with a power-law slope of $alpha_{rm lambda,diff}sim-2$,
further supporting that they belong to the same population with analogous
intrinsic variability mechanisms, e.g., rapid accretion rate change with a
possible state transition. Finally, we also confirm the anti-breathing of CIV
(i.e., line width increases as luminosity increases) in EVQs, and find that in
addition to $sim$ 0.4 dex systematic uncertainty in single-epoch CIV virial
black hole mass estimates, an extra scatter of $sim$ 0.3 dex will be
introduced by extreme variability.
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