Are cosmologically distant objects obscured by dust. A test using quasars

At large redshifts, dust obscuration should become severe. We examine the possibility that cosmologically distant quasars have been obscured (and reddened) due to intervening dust either within or between the galaxies. Assuming simple Schechter-like luminosity functions for quasars, simple power law-like evolution of their statistical properties, and dust having opacity proportional to lambda-1 and occurring in clumps of varying optical thickness, we calculate the expected distributions of observed quasar properties. An apparent cutoff at zroughly-equal3 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. The amounts of dusts contemplated in these models (which are somewhat larger than expected from the properties of nearby galaxies) would have prevented us from seeing very bright galaxies in the process of formation