THE FAINT GALAXY CONTRIBUTION TO THE DIFFUSE EXTRAGALACTIC BACKGROUND LIGHT

Models of the faint galaxy contribution to the diffuse extragalactic background light are presented, which are consistent with current data on faint galaxy number counts and redshifts. We predict the autocorrelation function of surface brightness fluctuations in the extragalactic diffuse light and determine how these predictions depend on the cosmological model and assumptions of biasing. We confirm that the recent deep infrared number counts are most compatible with a high density universe (OMEGA-0 almost-equal-to 1) and that the steep blue counts then require an extra population of rapidly evolving blue galaxies. The faintest presently detectable galaxies produce an interesting contribution to the extragalactic diffuse light, and still fainter galaxies may also produce a significant contribution. These faint galaxies still only produce a small fraction of the total optical diffuse background light, but on scales of a few arcminutes to a few degrees, they produce a substantial fraction of the fluctuations in the diffuse light. The amplitude and angular dependence of these fluctuations are dependent on the redshift distribution of the faint galaxies and on the background cosmological model. Measurement of the correlation function of fluctuations in the diffuse background light will place additional constraints on the redshift distribution and spatial clustering of these extremely faint galaxies.