Low surface brightness galaxies in the local universe .3. Implications for the field galaxy luminosity function

We present a luminosity function for low surface brightness (LSB) galaxies identified in the Automatic Plate Measuring Facility survey of Impey et al. These galaxies have central surface brightnesses [mu(0)] in B in the range 22.0 less than or equal to mu(0) less than or equal to 25.0. Using standard maximum likelihood estimators, we determine that the best-fit Schechter function parameters for this luminosity function (LF) are alpha = -1.42, M* = -18.34, and phi* = 0.0036, assuming H-0 = 100 h(100) km s(-1) Mpc(-1). We compare the luminosity and number densities derived from this luminosity function with those obtained from other recent field galaxy studies and find that surveys that do not take account of the observational selection bias imposed by surface brightness are missing a substantial fraction of the galaxies in the local universe. Under our most conservative estimates, our derivation of the LF for LSB galaxies suggests that the CfA Redshift Survey has missed at least one-third of the local galaxy population. This overlooked fraction is not enough by itself to explain the large number of faint blue galaxies observed at moderate redshift under no-evolution models, but it does help to close the gap between local and moderate-redshift galaxy counts.