High-redshift Extreme Variability Quasars from Sloan Digital Sky Survey Multiepoch Spectroscopy
Abstract
We perform a systematic search for high-redshift ( $z\,\gt $ 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 (≲1σ) 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2020
- DOI:
- 10.3847/1538-4357/abc2ce
- arXiv:
- arXiv:2006.08645
- Bibcode:
- 2020ApJ...905...52G
- Keywords:
-
- Active galactic nuclei;
- Quasars;
- black hole physics;
- Spectroscopy;
- Time domain astronomy;
- 16;
- 1319;
- 159;
- 1558;
- 2109;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 25 pages, 15 figures, 6 tables, published in ApJ