Extreme Variability Quasars from the Sloan Digital Sky Survey and the Dark Energy Survey

Journal Article · 21 February 2018 · The Astrophysical Journal (Online)

DOI: https://doi.org/10.3847/1538-4357/aaa9b6 · OSTI ID:1425676

Rumbaugh, N. ; Shen, Yue ; Morganson, Eric ; Liu, Xin; Banerji, M.; McMahon, R. G. ; Abdalla, F. B.; Benoit-Lévy, A.; Bertin, E.; Brooks, D. ; Buckley-Geer, E.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Cunha, C. E.; D’Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S. ; Doel, P.; Frieman, J.; García-Bellido, J. ; Gruen, D. ; Gruendl, R. A. ; Gschwend, J.; Gutierrez, G.; Honscheid, K.; James, D. J. ; Kuehn, K. ; Kuhlmann, S.; Kuropatkin, N.; Lima, M.; Maia, M. A. G.; Marshall, J. L. ; Martini, P. ; Menanteau, F.; Plazas, A. A. ; Reil, K.; Roodman, A. ; Sanchez, E. ; Scarpine, V.; Schindler, R.; Schubnell, M.; Sheldon, E.; Smith, M. ; Soares-Santos, M. ; Sobreira, F.; Suchyta, E.; Swanson, M. E. C. ; Walker, A. R. ; Wester, W.

Here, we perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey (SDSS) and 3-Year Dark Energy Survey (DES) imaging, which provide light curves spanning more than 15 years. We also identified 1000 EVQs with a maximum g band magnitude change 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 g.22 quasars over a baseline of 15 years. These EVQs are good candidates for so-called “changing-look quasars”, where a spectral transition between the two types of quasars (broad-line and narrow-line) is observed between the dim and bright states. We performed detailed multi-wavelength, spectral and variability analyses for the EVQs and compared 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 suggest that internal processes associated with accretion are the main driver for the observed extreme long-term variability. In spit of 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 accretion rates, where the accretion flow is more likely to experience instabilities that drive the factor of few changes in flux on multi-year timescales.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States); Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC), High Energy Physics (HEP)
• Contributing Organization: DES Collaboration
• Grant/Contract Number: AC02-76SF00515; AST-1138766; AYA2012-39559; ESP2013-48274; FPA2013-47986; 240672; 291329; 306478; SC0012704; AC02-07CH11359; AC05-00OR22725
• OSTI ID: 1425676
• Alternate ID(s): OSTI ID: 1389253; OSTI ID: 1409080; OSTI ID: 1435204
• Report Number(s): BNL-114280-2017-JA; FERMILAB-PUB-17-211-AE; arXiv:1706.07875; TRN: US1802147
• Journal Information: The Astrophysical Journal (Online), Vol. 854, Issue 2; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)Copyright Statement
• Country of Publication: United States
• Language: English