Background light from galaxies as a cosmological probe

Galaxies emit radiation that forms a background of intergalactic light. The energy density at the present epoch of this radiation field depends mainly on three things: (1) the epoch at which galaxies formed; (2) the luminosity evolution that galaxies have undergone since they formed; (3) the cosmology (and in particular the present value H0 of Hubble's parameter). We have calculated the expected energy density of the extragalactic background light (EBL) for (1) a range of galaxy formation epochs; (2) a range of luminosity-evolution parameters for galaxies (taking into account differing types of evolution for ellipticals and spirals); (3) a range of Robertson-Walker universe models (with and without the cosmological constant). We discuss how experiments presently being made to measure the EBL can be used to gain information on (1)--(3). Presently available upper limits on the EBL indicate that galaxies in general were not very much more luminous when young than they are now, or that H0 lies nearer H0=100 km sec-1 Mpc-1 than H0=50 km sec-1 Mpc-1, or possibly both