The morphologically divided redshift distribution of faint galaxies

We have constructed a morphologically divided redshift distribution of fain t held galaxies using a statistically unbiased sample of 196 galaxies brigh ter than I = 21.5 for which detailed morphological information (from the Hu bble Space Telescope) as well as ground-based spectroscopic redshifts are a vailable. Galaxies are classified into three rough morphological types acco rding to their visual appearance (E/S0s, spirals, Sdm/dE/Irr/Pec galaxies), and redshift distributions are constructed for each type. The most strikin g feature is the abundance of low- to moderate-redshift SSm/dE/Irr/Pec gala xies at I < 19.5. This confirms that the faint-end slope of the luminosity function (LF) is steep (alpha < - 1.4) for these objects. We also find that Sdm/dE/Irr/Pec galaxies are fairly abundant at moderate redshifts, and thi s can be explained by a strong luminosity evolution. However, the normaliza tion factor (or the number density) of the LF of Sdm/dE/Irr/Pec galaxies is not much higher than that of the local LF of Sdm/dE/Irr/Pec galaxies. Furt hermore, as we go to fainter magnitudes, the abundance of moderate- to high -redshift Irr/Pec galaxies increases considerably. This cannot be explained by strong luminosity evolution of the dwarf galaxy populations alone: thes e Irr/Pec galaxies are probably the progenitors of present-day ellipticals and spiral galaxies that are undergoing rapid star formation or merging wit h their neighbors. On the other hand, the redshift distributions of E/S0s a nd spirals are fairly consistent with those expected from passive luminosit y evolution and are only in slight disagreement with the nonevolving model.