Abstract
We perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey and 3 Year Dark Energy Survey imaging, which provide light curves spanning more than 15 years. We identified ∼1000 EVQs with a maximum change in g-band magnitude of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L bol ∼ 1045-1047 erg s-1 and L/L Edd ∼ 0.01-1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of ∼30%-50% among all quasars over a baseline of ∼15 yr. We performed detailed multi-wavelength, spectral, and variability analyses for the EVQs and compared them to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggests that internal processes associated with accretion are the main driver for the observed extreme long-term variability. However, despite their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low rates, where the accretion flow is more likely to experience instabilities that drive the changes in flux by a factor of a few on multi-year timescales.
Original language | English |
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Article number | 160 |
Journal | Astrophysical Journal |
Volume | 854 |
Issue number | 2 |
DOIs | |
State | Published - Feb 20 2018 |
Funding
We thank the referee, Andy Lawrence, for a constructive report that greatly improved this work, and Yan-Fei Jiang, Charles Gammie, Stephanie LaMassa, Chelsea MacLeod, Suvi Gezari, and Aaron Barth for useful comments on the manuscript. Y.S. acknowledges support from an Alfred P. Sloan Research Fellowship and NSF grant AST-1715579. The DES data management system is supported by the National Science Foundation under Grant Number AST-1138766. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2012-39559, ESP2013-48274, FPA2013-47986, and Centro de Excelencia Severo Ochoa SEV-2012-0234. Research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme FP7/2007-2013) including ERC grant agreements 240672, 291329, and 306478. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and Astro-Particle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência, Tecnologia e Inovação, the Deutsche Forschungs-gemeinschaft and the Collaborating Institutions in the DES. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web site ishttp://www.sdss.org/. Y.S. acknowledges support from an Alfred P. Sloan Research Fellowship and NSF grant AST-1715579. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and Astro-Particle Physics at the Ohio State University.
Funders | Funder number |
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Centro de Excelencia Severo Ochoa | SEV-2012-0234 |
Deutsche Forschungs-gemeinschaft | |
Kavli Institute of Cosmological Physics at the University of Chicago | |
Ministry of Science and Education of Spain | |
Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University | |
National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign | |
U.S. National Science Foundation | |
National Science Foundation | AST-1715579, AST-1138766 |
U.S. Department of Energy | |
National Aeronautics and Space Administration | |
Alfred P. Sloan Foundation | |
University of Illinois at Urbana-Champaign | |
Ohio State University | |
Seventh Framework Programme | 1138766, 240672, 306478, 1715579, 291329 |
Higher Education Funding Council for England | |
Center for Cosmology and Astroparticle Physics, Ohio State University | |
Engineering Research Centers | |
Science and Technology Facilities Council | |
Higher Education Funding Council for England | |
European Research Council | |
Ministerio de Economía y Competitividad | FPA2013-47986, AYA2012-39559, ESP2013-48274 |
Ministério da Ciência, Tecnologia e Inovação | |
Conselho Nacional de Desenvolvimento Científico e Tecnológico | |
Max-Planck-Gesellschaft | |
Norsk Sykepleierforbund | |
Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro | |
Financiadora de Estudos e Projetos | |
Seventh Framework Programme |
Keywords
- black hole physics
- galaxies: active
- line: profiles
- quasars: general
- surveys