Studies of Quasar Variability With the Sloan Digital Sky Survey

Details Studies of Quasar Variability With the Sloan Digital Sky Survey Studies of Quasar Variability With the Sloan Digital Sky Survey

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.7224w&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #72.24; Bulletin of the American Astronomical Society, V

Physics

Scientific paper

This poster summarizes the recent work within the Sloan Digital Sky Survey collaboration to study quasar physics through monitoring of their optical variability. SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for 2500 quasars observed more than 50 days apart. In the SDSS equatorial stripe, almost 10,000 spectroscopically confirmed quasars have been imaged at an average of 10 epochs with a baseline of 4 years. This marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 Angstroms. Also, we find a strong correlation between the change in the C IV line flux and the change in the line width. The relation between line flux change and line width change is consistent with a model in which a broad line base varies with greater amplitude than the line core. In addition, we find no evidence for variability of the well-known blueshift of the C IV line with respect to the low-ionization Mg II line in the highest flux objects, indicating that this blueshift might be useful as a measure of orientation. We have also studied the variability of broad absorption troughs for a subsample of these objects. For these objects, we observe that the strongest BAL variability occurs among the smallest equivalent width features, and at velocities exceeding 12,000 km/s, as predicted by recent disk-wind modeling. Most recently, using the repeat photometric scans of quasars in the SDSS equatorial stripe, we have found evidence that, for a given quasar luminosity, optical variability is directly related to the mass of the central black hole. This points towards Eddington ratio as one of the main drivers of quasar variability.

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