The Contribution of Low Surface-Brightness Galaxies to Faint Galaxy Counts

Low Surface-Brightness (LSB) galaxies are severely underrepresented in surveys used to define the local luminosity function (LF), but could it in principle be detected in deep surveys. To explore the possible contribution of such objects to faint galaxy counts, we construct catalogs of simulated non-evolving galaxies drawn from a multivariate distribution of galaxy luminosities, central surface brightnesses, bulge/disk ratios and spectral-energy distributions. We compare two models dominated by LSB galaxies to a standard non-evolving model. Model galaxies are convolved with seeing and selected in a manner that closely matches real surveys. For each model we compute the local LF, HI mass function, number counts, redshift and color distributions. We find it possible to include a large population of LSB galaxies and incorporate a steep faint-end slope of the LF in our simulations without violating the constraints on the local LF or HI mass function. For $q_0 = 0.5$, the most favorable model matches the counts to B=23, but falls short of the observations at fainter magnitudes. The colors and redshift distributions remain roughly consistent with observations to B=24. The most serious discrepancy with observations is in the distribution of $r_e$ at faint magnitudes, suggesting that the model contains too many LSB galaxies. Nevertheless, the results suggest that LSB galaxies could be a significant contributor to faint-galaxy counts, reducing the need for such extreme models of galaxy evolution as rapid merging or bursting dwarf galaxies.