<><><><><><><><><><><><><><><><><><>

NOAO/KPNO - NSO,

DEPARTMENT OF ASTRONOMY

AND STEWARD OBSERVATORY

AND NRAO

The University of Arizona

<><><><><><><><><><><><><><><><><><>

JOINT COLLOQUIUM

DR. PATRICK HALL

Pontificia Universidad Catolica de Chile

"Red Quasars"

Thursday, February 13, 2003

4:00 p.m.

Steward Observatory

Lecture Hall - Room N210

Abstract: Quasars have intrinsically blue spectra, which makes them easy to locate and study. But heavily obscured active galactic nuclei are also known to exist, in the form of radio galaxies or Seyfert 2s with broad lines seen in polarized light, for example. In between these extremes we should find a population of dust-reddened quasars. I discusss recent results on such quasars, primarily from the Sloan Digital Sky Survey. In a sample of 4576 SDSS quasars, 6 percent appear to be dust reddened. More than just dust reddening appears to be at work, since these quasars have narrower Balmer lines than unreddened quasars, as well as other spectral differences. Nonetheless, the color distribution of SDSS quasars contains information on the distribution of reddenings around quasars, which determines the relative contributions of unreddened, moderately reddened, and obscured quasars to the total population of luminous AGN.

**Refreshments at 3:30PM in the Lobby**