Kavli Affiliate: Rafe Schindler
| First 5 Authors: Qian Yang, Yue Shen, Yu-Ching Chen, Xin Liu, James Annis
| Summary:
We present new Gemini/GMOS optical spectroscopy of 16 extreme variability
quasars (EVQs) that dimmed by more than 1.5 mag in the $g$ band between the
Sloan Digital Sky Survey (SDSS) and the Dark Energy Survey (DES) epochs
(separated by a few years in the quasar rest frame). The quasar sample covers a
redshift range of $0.5 < z < 2.1$. Nearly half of these EVQs brightened
significantly (by more than 0.5 mag in the $g$ band) in a few years after
reaching their previous faintest state, and some EVQs showed rapid (non-blazar)
variations of greater than 1-2 mag on timescales of only months. Leveraging on
the large dynamic range in continuum variability between the earlier SDSS and
the new GMOS spectra, we explore the associated variations in the broad Mg
II,$lambda2798$ line, whose variability properties have not been well studied
before. The broad Mg II flux varies in the same direction as the continuum
flux, albeit with a smaller amplitude, which indicates at least some portion of
Mg II is reverberating to continuum changes. However, the width (FWHM) of Mg II
does not vary accordingly as continuum changes for most objects in the sample,
in contrast to the case of the broad Balmer lines. Using the width of broad Mg
II to estimate the black hole mass therefore introduces a luminosity-dependent
bias.
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