Probing galaxy formation with TeV gamma ray absorption

We present here the extragalactic background light (EBL) predicted by semi- analytic models of galaxy formation, and show how measurements of the absor ption of gamma rays of similar to TeV energies via pair production on the E EL can probe cosmology and the formation of galaxies. Semi-analytic models permit a physical treatment of the key processes of galaxy formation - incl uding gravitational collapse and merging of dark matter halos, gas cooling and dissipation, star formation, supernova feedback and metal production - and have been shown to reproduce key observations at low and high redshift. Using this approach, we investigate the consequences of variations in inpu t assumptions such as the stellar initial mass function and the underlying cosmology. We conclude that observational studies of the absorption of simi lar to 10(-2)-10(2) TeV gamma rays will help to constrain the star formatio n history of the universe, and the nature and extent of the extinction of s tarlight due to dust and reradiation of the absorbed energy at infrared wav elengths. (C) 1999 Elsevier Science B.V. All rights reserved.