Spectral variability of quasars in the Sloan Digital Sky Survey

Details Spectral variability of quasars in the Sloan Digital Sky Survey Spectral variability of quasars in the Sloan Digital Sky Survey

Aug 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........11w&link_type=abstract

Ph.D dissertation, 2004. 118 pages; United States -- Illinois: The University of Chicago; 2004. Publication Number: AAT 3149369

Computer Science

Spectral Variability, Quasars, Sloan Digital Sky Survey

Scientific paper

Sloan Digital Sky Survey (SDSS) repeat spectroscopic observations have resulted in multiple-epoch spectroscopy for ~2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 Å to 6000 Å. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index a l = -2.00, compared to an index of a l = -1.35 for the single-epoch spectrum. The difference spectrum also exhibits very weak or absent emission line features. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases, but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for l rest < 2500 Å, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.
We also examine the variability of the high-ionizaton C IVl1549 line in a sample of 105 quasars observed at multiple epochs. We find a strong correlation between the change in the C IV line flux and the change in the line width, but no correlations between the change in flux and changes in line center and skewness. 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. Using moment analysis line-fitting techniques, we measure line fluxes, centers, widths and skewnesses for the C IV line at two epochs for each object. The well-known Baldwin Effect is seen for these objects, with a slope b = -0.12. The sample has a median intrinsic Baldwin Effect slope of b int = -0.86; the C IV lines in these high-luminosity quasars appear to be less responsive to continuum variations than those in lower luminosity objects. Additionally, we find no evidence for variability of the well known blueshift of the C IV line with respect to the low-ionization Mg IIl2798 line in the highest flux objects, indicating that this might be useful as a measure of orientation.

Affiliated with

Also associated with

No associations

Rating

Spectral variability of quasars in the Sloan Digital Sky Survey does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Spectral variability of quasars in the Sloan Digital Sky Survey, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spectral variability of quasars in the Sloan Digital Sky Survey will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1098022