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P. B. Hall (Princeton / Catolica), G. T. Richards (Princeton)
The optical/UV color distribution of quasars in the Sloan Digital Sky Survey (SDSS) can be described as Gaussian plus a red tail. Using a sample of 4576 homogenously selected quasars, we show that the SDSS can distinguish between quasars with intrinsically red power-law continua and those that are reddened and extincted by dust. Dust-reddened quasars dominate the `anomalously red quasars' in the red tail of the color distribution. Despite the fact that the SDSS Quasar Survey is optically selected and flux-limited, it is quite sensitive to such quasars, which constitute 6 percent of our sample. This is a firm lower limit to the population of dust reddened quasars that may be missed by flux-limited ultra-violet excess quasar surveys. Investigating the spectral properties of our sample as a function of color, we find that quasars with intrinsically red power-law continua tend to have narrower Balmer lines and weaker CIV, CIII], HeII and Balmer continuum emission as compared to bluer quasars. The anomalously red quasars have even narrower Balmer lines and weaker Balmer continua, in addition to having much larger equivalent widths of narrow [OII] and [OIII] emission. The narrower Balmer lines in anomalously red quasars rule out a simple foreground screen model of reddening as the dominant reddening mechanism. The effects of orientation, line(s) of sight, and/or dust intrinsic to the inner regions of the quasars must all be considered.
The author(s) of this abstract have provided an email address for comments about the abstract: pathall@astro.princeton.edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.