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G.T. Richards (Penn State,Chicago), X. Fan (IAS), D.P. Schneider (Penn State), D.E. Vanden Berk (Fermilab), M.A. Strauss (Princeton), D.G. York (Chicago), SDSS Collaboration
We present an empirical investigation of the colors of quasars in the Sloan Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625 quasars with SDSS photometry: 1759 quasars found during SDSS spectroscopic commissioning and SDSS followup observations on other telescopes, 50 matches to FIRST quasars, 573 matches to quasars from the NASA Extragalactic Database, and 243 quasars from two or more of these sources. The quasars are distributed in a 2.5 degree wide stripe centered on the Celestial Equator covering ~529 square degrees. New SDSS quasars, which range in brightness from i* = 15.39 to the photometric magnitude limit of the survey, represent an increase of over 200% in the number of known quasars in this area of the sky.
The ensemble average of the observed colors of quasars in the SDSS passbands are well represented by a power-law continuum with \alpha\nu = -0.5 (f\nu \propto \nu\alpha) and are close to those predicted by previous simulations. However, the contributions of the ``small blue (or 3000\,{\rm Å}) bump'' and other strong emission lines have a significant effect upon the colors. The color-redshift relation exhibits considerable structure, which may be of use in determining photometric redshifts for quasars from their colors alone. The range of colors at a given redshift can generally be accounted for by a range in the optical spectral index with a distribution of \alpha\nu=-0.5±0.65 (95%~confidence), but there is a red tail in the distribution. This tail is likely to be a sign of internal reddening, especially since fainter objects at a given redshift tend to exhibit redder colors than the average. Finally, we show that there is a continuum of properties between quasars and Seyfert galaxies and we test the validity of the traditional dividing line (MB=-23) between the two classes of AGN.