In:
The Astrophysical Journal, American Astronomical Society, Vol. 905, No. 1 ( 2020-12-01), p. 52-
Abstract:
We perform a systematic search for high-redshift ( 1.5) extreme variability quasars (EVQs) using repeat spectra from the Sixteenth Data Release of the Sloan Digital Sky Survey, which provides a baseline spanning up to ∼18 yr in the observed frame. We compile a sample of 348 EVQs with a maximum continuum variability at rest frame 1450 Å of more than 100% (i.e., δV ≡ (Max − Min)/Mean 〉 1). The EVQs show a range of emission-line variability, including 23 where at least one line in our redshift range disappears below detectability, which can then be seen as analogous to low-redshift changing-look quasars (CLQs). Importantly, spurious CLQs caused by problematic SDSS spectral flux calibration, e.g., fiber-drop issue, have been rejected. The similar properties (e.g., continuum/line, difference-composite spectra and Eddington ratio) of normal EVQs and CLQs imply that they are basically the same physical population with analogous intrinsic variability mechanisms, as a tail of a continuous distribution of normal quasar properties. In addition, we find no reliable evidence (≲1 σ ) to support that CLQs are a subset of EVQs with less efficient accretion. Finally, we also confirm the antibreathing of C iv (i.e., the line width increases as luminosity increases) in EVQs and find that in addition to the ∼0.4 dex systematic uncertainty in single-epoch C iv virial black hole mass estimates, an extra scatter of ∼0.3 dex will be introduced by extreme variability.
Type of Medium:
Online Resource
ISSN:
0004-637X
,
1538-4357
DOI:
10.3847/1538-4357/abc2ce
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2020
detail.hit.zdb_id:
2960-9
detail.hit.zdb_id:
1473835-1
SSG:
16,12
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