Is the luminosity distribution of field galaxies really flat ?

Abstract

Recent observations of the galaxy population within rich clusters have found a characteristic luminosity distribution described by a flat (alpha = -1.0) Schechter function which exhibits an upturn at faint absolute magnitudes (B Mag = -18). Here we discuss whether such a form for the field luminosity distribution is ruled out by local and/or faint magnitude limited redshift surveys (MLRS). Our conclusions are that existing redshift surveys provide little constraints on the volume-density distribution of field galaxies faintwards of B Mag = -18. The local MLRS suffer from poor statistics over inhomogeneous volumes, while the faint MLRS are ambiguous because of the unknown nature of the ``faint blue excess'' and the ``normalization'' problem. Adopting a functional form similar to that seen in rich clusters we find that the maximum allowable faint end slope, based on the Mt Stromlo-APM redshift survey, is $\hat{I}\pm \approx -1.8$ faintwards of B Mag = -18.0 (Ho = 50 km/s/Mpc^{3}).

To appear in The Astrophysical Journal (Sept 20th, 1996). 27 pages including 4 figures (gzipped uuencoded)