The faint-end of the cluster galaxy luminosity function.

Abstract

The galaxy luminosity function (LF) is a fundamental tool for understanding galaxy evolution and faint galaxy populations. The shape of the cluster LF provides information on the initial formation and subsequent evolution of galaxies in clusters while the power law slope at the faint end indicates how steeply the dwarf galaxy number counts rise and, assuming a mass to light ratio such as has been found for Local Group dwarfs, how much mass the dwarfs may contribute to the total mass of the cluster. In previous studies of the cluster LF, differences have been found in its shape and the faint-end slope. While cluster environmental effects may be the cause of this range in values for the slope, the range may also be a consequence of the different detection and reduction techniques. We have constructed deep <italic>V</italic>-band luminosity functions for 5 Abell clusters with the goal of measuring the faint-end slopes, establishing whether the cluster galaxy LF is universal, estimating the mass contribution to galaxy clusters by the dwarf population, assessing whether environmental factors impact the shape of the galaxy LF, and, if so, determining which factors may be important in influencing the dwarf galaxy population. We have carefully dealt with the selection effects inherent in the detection and classification of faint, low surface brightness galaxies through false galaxy analysis. We determine that we are complete to 25 mag arcsec<super>-2</super> and to M<italic>_V</italic> &sim; -13.0 for each of the clusters. We do not believe we are missing a significant population of low surface brightness galaxies brighter than this limiting magnitude. We find similar faint-end slopes of alpha &sim; -1.4 for three of our clusters. A fourth suffers from background structure contamination but is consistent with also having a similar slope. With this shallow of a slope, dwarfs can only account for 20% of the cluster mass from galaxies. We find no strong evidence for environmental effects acting on the LF. Although cosmic variance adds a large source of uncertainty to the LF determination, we are able to tightly constrain the value of the faint-end slope, at least for these clusters.