The luminosity function of galaxies to $M_{BgVriz} \sim -14$ in $z \sim 0.3$ clusters

Abstract

We present deep composite luminosity functions in $B$, $g$, $V$, $r$, $i$ and $z$ for six clusters at $0.14 < z < 0.40$ observed with the Hubble Space Telescope Advanced Camera for Surveys. The luminosity functions reach to absolute magnitude of $\sim -14 + 5\log h$ mag. and are well fitted by a single Schechter function with $M^*_{BgVriz}=-19.8, -20.9 -21.9, -22.0, -21.7, -22.3$ mag. and $\alpha \sim -1.3$ (in all bands). The observations suggest that the galaxy luminosity function is dominated by objects on the red sequence to at least 6 mags. below the $L^*$ point. Comparison with local data shows that the red sequence is well established at least at $z \sim 0.3$ down to $\sim 1/600^{th}$ of the luminosity of the Milky Way and that galaxies down to the regime of dwarf spheroidals have been completely assembled in clusters at this redshift. We do not detect a steepening of the luminosity function at $M > -16$ as is observed locally. If the faint end upturn is real, the steepening of the luminosity function must be due to a newly infalling population of faint dwarf galaxies.