Dust Reddening in Sloan Digital Sky Survey Quasars

We explore the form of extragalactic reddening toward quasars using a sample of 9566 quasars with redshifts 0 z 2.2, and accurate optical colors from the Sloan Digital Sky Survey (SDSS). We confirm that dust reddening is the primary explanation for the red “tail ” of the color distribution of SDSS quasars. Our fitting to 5-band photometry normalized by the modal quasar color as a function of redshift shows that this “tail ” is well described by SMC-like reddening but not by LMC-like, Galactic, or Gaskell et al. (2004) reddening. Extension to longer wavelengths using a subset of 1886 SDSS-2MASS matches confirms these results at high significance. We carry out Monte-Carlo simulations that match the observed distribution of quasar spectral energy distributions using a Lorentzian dust reddening distribution; 2 % of quasars selected by the main SDSS targeting algorithm (i.e., which are not extincted out of the sample) have EB−V 0.1; less than 1 % have EB−V 0.2, where the extinction is relative to quasars with modal colors. Reddening is uncorrelated with the presence of intervening narrow-line