The luminosity function of compact groups of galaxies

Abstract

We present an analysis of the luminosity function of the galaxies in Hickson's sample of compact groups (HCG). The luminosities of compact group galaxies are consistent with their being drawn from a Schechter luminosity function with α = -0.2^+0.8^_-0.9_, L^*^ = 1.1 +/- 0.2 x 10^10^ h^-2^L_sun_ and {PHI}^*^ = 1.3^+0.2^_-0.8_ x 10^-4^ h^3^ Mpc^-3^ (99% confidence level). Individual morphological-type luminosity functions were also determined. Both the total and morphological-type specific luminosity functions of compact group galaxies are significantly different from those of field, loose-group, and cluster galaxies. In particular, the luminosity function of HCG elliptical galaxies has a mean magnitude which is significantly brighter than the mean magnitude of Virgo cluster elliptical galaxies (28% of HCG elliptical galaxies are more luminous than M87). The mean luminosity density of galaxies in compact groups is estimated to be L = 1.3^+0.1^_-0.8_ x 10^6^ h L_sun_ Mpc^-3^, which constitutes 0.8% of the total luminosity density of galaxies in the universe. This result is consistent with the conventional scenario in which compact groups merge to form elliptical galaxies on a relatively short time scale.