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 spectroscopic 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 systematically steepen and progress toward more luminous galaxies with increasing lookback time, assuming that the galaxy redshift distribution may be smoothly extrapolated 2 mag fainter than observed, as suggested by recent gravitational lensing studies. This evolution is shown to be color-dependent, and we predict the near-infrared color distribution of faint galaxies. The luminosity function of blue (B-K less than or similar to 4) galaxies in the range 0.2 less than or similar to z less than or similar to 1 can be represented by a Schechter function with characteristic light density phi(*)L(*) comparable to that of present-day late-type galaxies, but with a steeper faint end slope alpha approximate to 1.4.