Optically identified QSO absorption systems and galaxy evolution

Abstract

A comprehensive set of all available magnitudes, colors and redshifts for optically identified QSO absorbers is compiled from the literature. This results in a largely unbiased sample of galaxies at high redshifts, the size of the sample being reasonably large to allow for a first comparison with galaxy evolution models. We use our evolutionary spectral synthesis models describing various spectral types of galaxies with appropriate star formation histories. For a standard cosmology H0=50, Omega0=1, we find that all identified QSO absorbers up to a redshift about z=2 do fall within the evolving range of models which had been shown earlier to give good agreement with nearby galaxies of various spectral types. The most striking result is that all spectral types of galaxies from E through Sd seem to be present in this absorber candidate sample with the bulk of the objects being spirals of type Sa to Sc. We also show that such kind of high redshift galaxy sample should allow for significant restrictions of the cosmological parameters. While models with H0=50, Omega0=1 and any redshift of galaxy formation zform=5 ... 10 give reasonable agreement with observed luminosities and colors, present data seem to exclude the combination H0=50, Omega0=0.1. A low Omega0 together with a value of H0 > 50 might still be viable. Additional data, and in particular observations of absorbing galaxies in more than one passband, are required for further constraints. We realize that the present results depend on the adopted evolutionary models and on the input physics used which might be better constrained by future observations.