Are cosmologically distant objects obscured by dust? - A test using quasars

Abstract

At large redshifts, dust obscuration should become severe. The possibility that cosmologically distant quasars have been obscure (and reddened) due to intervening dust either within or between the galaxies are examined. Assuming simple Schechter-like luminosity functions for quasars, simple power law-like evolution of their statistical properties, and dust having opacity proportional to the inverse of lambda and occurring in clumps of varying optical thickness, the expected distributions of observed quasar properties are calculated. An apparent cutoff at z approximately equal to 3 is easily obtained for reasonable dust parameters without producing excessive reddening. Other predicted properties are also consistent with observations. The main drawback of the model is that there is a danger of producing more X-ray flux from optically obscured quasars than is observed. Conversely, the best test of the obscuration hypothesis will come from a search to find reddened quasars where, at present, blank field X-ray or radio sources are detected.