• DOI:10.3847/1538-4357/ab05e2
• Corpus ID: 119095051

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

@article{MacLeod2018ChanginglookQC,
  title={Changing-look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars},
  author={Chelsea L. MacLeod and Paul J. Green and Scott F. Anderson and Alastair Bruce and Michael Eracleous and Matthew J. Graham and David Homan and Andy Lawrence and Amy Lebleu and Nicholas P. Ross and John J. Ruan and Jessie C. Runnoe and Daniel Stern and William S. Burgett and K. C. Chambers and Nicholas Kaiser and Eugene A. Magnier and Nigel Metcalfe},
  journal={The Astrophysical Journal},
  year={2018},
  volume={874}
}

• C. MacLeod, P. Green, +15 authors N. Metcalfe
• Published 28 September 2018
• Physics
• The Astrophysical Journal

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 ( mag, 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 ≳20%. 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.