THE FAINT END OF THE GALAXY LUMINOSITY FUNCTION

The evolution of the B- and K-band luminosity functions of galaxies is inferred in a relatively model-independent way from deep spectroscopi c and photometric surveys. We confirm earlier evidence by Eales for an increase in the amplitude of the B-band galaxy luminosity function at modest redshift (z less than or similar to 0.2). We find in addition that the slope of the faint end of the luminosity function must system atically steepen and progress toward more luminous galaxies with incre asing lookback time, assuming that the galaxy redshift distribution ma y be smoothly extrapolated 2 mag fainter than observed, as suggested b y recent gravitational lensing studies. This evolution is shown to be color-dependent, and we predict the near-infrared color distribution o f faint galaxies. The luminosity function of blue (B-K less than or si milar to 4) galaxies in the range 0.2 less than or similar to z less t han or similar to 1 can be represented by a Schechter function with ch aracteristic light density phi()L(*) comparable to that of present-da y late-type galaxies, but with a steeper faint end slope alpha approxi mate to 1.4.