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Quasars Toggling in Real-time: Changing-Look Quasars from Multi-Epoch Spectroscopy in The Time Domain Spectroscopic Survey of SDSS-IV

Presentation #335.06 in the session AGN and Quasars VI.

Published onJun 29, 2022
Quasars Toggling in Real-time: Changing-Look Quasars from Multi-Epoch Spectroscopy in The Time Domain Spectroscopic Survey of SDSS-IV

Active galactic nuclei (AGN) can vary significantly in their rest-frame optical/UV continuum emission, sometimes with strong associated changes in broad line emission occurring on much shorter timescales than predicted by standard models of accretion disks around supermassive black holes. The Time Domain Spectroscopic Survey of SDSS-IV obtained repeat spectroscopy of large numbers of previously-known quasars, with spectral epochs separated by months to decades. Visual examination of these repeat spectra for strong broad line variability yielded 61 newly-discovered CLQ candidates. By defining a CLQ to have least a 3σ variation of broad Hβ emission, we find 19 CLQs, of which 15 are newly-recognized. Since the parent sample includes only broad line quasars, our study tends to find objects that have dimmed, i.e., turn-off CLQs. However, we nevertheless find 4 bona fide turn-on CLQs. We study the response of both H beta and MgII emission lines to continuum changes. The Eddington ratios of CLQs is low, and/or their Hβ broad line width is large relative to the overall quasar population. Repeat quasar spectroscopy in the upcoming SDSS-V Black Hole Mapper program promises to reveal significant numbers of CLQs, helping to further our understanding of the frequency and duty-cycle of such strong variability, and constrain the physics and dynamics of the phenomenon.

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