EXTRAGALACTIC BACKGROUND LIGHT - THE CONTRIBUTION BY FAINT AND LOW SURFACE BRIGHTNESS GALAXIES

Several models which have been constructed to explain the faint galaxy excess in observed number counts are used to predict the intensity of the extragalactic background light (EBL). Special attention is given to irregular and dwarf galaxies, which seem to be more common in the u niverse than once thought, and to low surface brightness galaxies (LSB ), which can in principle be altogether missed from galaxy counts. The nature of the latter objects is still unclear, but some plausible mod els predict that LSB galaxies can increase the intensity of the EBL by a factor of up to 5 from a standard, no-evolution model in the optica l and near infrared and by an order of magnitude in the UV. If the fai nt excess population consists of low-luminosity dwarfs, whose luminosi ty function has a steep faint end, the EBL can well increase by a fact or of 3 to 5, while still being consistent with current number count d ata. The resulting values of the EBL are not far from the observed upp er limits. In the future the overall level of the EBL and its spectral distribution could be used to differentiate between galaxy population models.