The sloan digital sky survey reverberation mapping project : ensemble spectroscopic variability of quasar broad emission lines
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We explore the variability of quasars in the Mg ii and Hβ broad emission lines and ultraviolet/optical continuum emission using the Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM). This is the largest spectroscopic study of quasar variability to date: our study includes 29 spectroscopic epochs from SDSS-RM over 6 months, containing 357 quasars with Mg ii and 41 quasars with Hβ . On longer timescales, the study is also supplemented with two-epoch data from SDSS-I/II. The SDSS-I/II data include an additional 2854 quasars with Mg ii and 572 quasars with Hβ . The Mg ii emission line is significantly variable (Δƒ/ƒ ~ 10% on ~100-day timescales), a necessary prerequisite for its use for reverberation mapping studies. The data also confirm that continuum variability increases with timescale and decreases with luminosity, and the continuum light curves are consistent with a damped random-walk model on rest-frame timescales of ≳5 days. We compare the emission-line and continuum variability to investigate the structure of the broad-line region. Broad-line variability shows a shallower increase with timescale compared to the continuum emission, demonstrating that the broad-line transfer function is not a δ-function. Hβ is more variable than Mg ii (roughly by a factor of ~1.5), suggesting different excitation mechanisms, optical depths and/or geometrical configuration for each emission line. The ensemble spectroscopic variability measurements enabled by the SDSS-RM project have important consequences for future studies of reverberation mapping and black hole mass estimation of 1<픃<2 quasars.
Sun , M , Trump , J R , Shen , Y , Brandt , W N , Dawson , K , Denney , K D , Hall , P B , Ho , L C , Horne , K D , Jiang , L , Richards , G T , Schneider , D P , Bizyaev , D , Kinemuchi , K , Oravetz , D , Pan , K & Simmons , A 2015 , ' The sloan digital sky survey reverberation mapping project : ensemble spectroscopic variability of quasar broad emission lines ' Astrophysical Journal , vol 811 , no. 1 . DOI: 10.1088/0004-637X/811/1/42
© 2015. The American Astronomical Society. All rights reserved. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at http://dx.doi.org/10.1088/0004-637X/811/1/42
M.Y.S. acknowledges support from the China Scholarship Council (No. 3009). J.R.T. and Y.S. acknowledge support from NASA through Hubble Fellowship grants #51330 and #51314, respectively, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26555. W.N.B. acknowledges support from NSF grant AST-1108604 and the V. M. Willaman Endowment. KDD is supported by an NSF AAPF fellowship awarded under NSF grant AST-1302093.