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Changing-look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars

MacLeod, Chelsea L.; Green, Paul J.; Anderson, Scott F.; Bruce, Alastair; Eracleous, Michael; Graham, Matthew; Homan, David; Lawrence, Andy; LeBleu, Amy; Ross, Nicholas P.; Ruan, John J.; Runnoe, Jessie; Stern, Daniel; Burgett, William; Chambers, Kenneth C.; Kaiser, Nick; Magnier, Eugene; Metcalfe, Nigel

Changing-look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars Thumbnail


Authors

Chelsea L. MacLeod

Paul J. Green

Scott F. Anderson

Alastair Bruce

Michael Eracleous

Matthew Graham

David Homan

Andy Lawrence

Amy LeBleu

Nicholas P. Ross

John J. Ruan

Jessie Runnoe

Daniel Stern

William Burgett

Kenneth C. Chambers

Nick Kaiser

Eugene Magnier



Abstract

Active galactic nuclei (AGNs) that show strong rest-frame optical/UV variability in their blue continuum and broad line emission are classified as changing-look AGN, or at higher luminosities, changing-look quasars (CLQs). These surprisingly large and sometimes rapid transitions challenge accepted models of quasar physics and duty cycles, offer several new avenues for study of quasar host galaxies, and open a wider interpretation of the cause of differences between broad and narrow-line AGN. To better characterize extreme quasar variability, we present follow-up spectroscopy as part of a comprehensive search for CLQs across the full Sloan Digital Sky Survey (SDSS) footprint using spectroscopically confirmed quasars from the SDSS DR7 catalog. Our primary selection requires large-amplitude ($| {\rm{\Delta }}g| \gt 1$ mag, $| {\rm{\Delta }}r| \gt 0.5$ mag) variability over any of the available time baselines probed by the SDSS and Pan-STARRS 1 surveys. We employ photometry from the Catalina Sky Survey to verify variability behavior in CLQ candidates where available, and confirm CLQs using optical spectroscopy from the William Herschel, MMT, Magellan, and Palomar telescopes. For our adopted signal-to-noise ratio threshold on variability of broad Hβ emission, we find 17 new CLQs, yielding a confirmation rate of gsim20%. These candidates are at lower Eddington ratio relative to the overall quasar population, which supports a disk-wind model for the broad line region. Based on our sample, the CLQ fraction increases from 10% to roughly half as the continuum flux ratio between repeat spectra at 3420 Å increases from 1.5 to 6. We release a catalog of more than 200 highly variable candidates to facilitate future CLQ searches.

Citation

MacLeod, C. L., Green, P. J., Anderson, S. F., Bruce, A., Eracleous, M., Graham, M., …Metcalfe, N. (2019). Changing-look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars. Astrophysical Journal, 874(1), Article 8. https://doi.org/10.3847/1538-4357/ab05e2

Journal Article Type Article
Acceptance Date Feb 6, 2019
Online Publication Date Mar 15, 2019
Publication Date Mar 31, 2019
Deposit Date Apr 2, 2019
Publicly Available Date Apr 2, 2019
Journal Astrophysical Journal
Print ISSN 0004-637X
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 874
Issue 1
Article Number 8
DOI https://doi.org/10.3847/1538-4357/ab05e2

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Copyright Statement
© 2019. The American Astronomical Society. All rights reserved.





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