Cosmological obscuration by galactic dust: effects of dust evolution

We explore the effects of dust in cosmologically distributed intervening galaxies in a high-redshift universe using a generalized model where dust content evolves with cosmic time. The absorbing galaxies are modelled as exponential discs 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 B-band optical depth to redshifts z greater than or similar to 1 by at least 60 per cent 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 derived evolution in space density.