Cosmological Obscuration by Galactic Dust: Effects of Dust Evolution

We explore the effects of dust in cosmologically distributed intervening galaxies on the high redshift universe using a generalised model where dust content evolves with cosmic time. The absorbing galaxies are modelled as exponential disks which form coevally, maintain a constant space density and evolve in dust content at a rate that is uniform throughout. We find that the inclusion of moderate to moderately weak amounts of evolution consistent with other studies can reduce the mean observed Bband optical depth to redshifts z∼1 by at least 60% relative to non-evolving models. Our predictions imply that intervening galactic dust is unlikely to bias the optical counts of quasars at high redshifts and their evolution in space density derived therefrom.