Spectral variability of a sample of extreme variability quasars and implications for the Mg II broad-line region

Qian Yang, Yue Shen, Yu Ching Chen, Xin Liu, James Annis, Santiago Avila, Emmanuel Bertin, David Brooks, Elizabeth Buckley-Geer, Aurelio Carnero Rosell, Matias Carrasco Kind, Jorge Carretero, Luiz da Costa, Shantanu Desai, H. Thomas Diehl, Peter Doel, Josh Frieman, Juan Garcia-Bellido, Enrique Gaztanaga, David GerdesDaniel Gruen, Robert Gruendl, Julia Gschwend, Gaston Gutierrez, Devon L. Hollowood, Klaus Honscheid, Ben Hoyle, David James, Elisabeth Krause, Kyler Kuehn, Christopher Lidman, Marcos Lima, Marcio Maia, Jennifer Marshall, Paul Martini, Felipe Menanteau, Ramon Miquel, Andrés Plazas Malagón, Eusebio Sanchez, Vic Scarpine, Rafe Schindler, Michael Schubnell, Santiago Serrano, Ignacio Sevilla, Mathew Smith, Marcelle Soares-Santos, Flavia Sobreira, Eric Suchyta, Molly Swanson, Gregory Tarle, Vinu Vikram, Alistair Walker

Research output: Contribution to journalArticlepeer-review


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 epochs (separated by a few years in the quasar rest frame). These EVQs are selected from quasars in the SDSS Stripe 82 region, covering 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 time-scales of only months. To increase sample statistics, we use a supplemental sample of 33 EVQs with multi-epoch spectra from SDSS that cover the broad Mg II λ2798 line. Leveraging on the large dynamic range in continuum variability between the multi-epoch spectra, we explore the associated variations in the broad Mg II 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 full width at half-maximum (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 with single epoch spectra therefore introduces a luminosity-dependent bias.

Original languageEnglish (US)
Pages (from-to)5773-5787
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Apr 1 2021


  • Black hole physics
  • Galaxies: active
  • Line: profiles
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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