The luminosity function of nearby galaxy clusters. II. Redshifts and luminosity function for galaxies in the region of the Centaurus Cluster

We acquired spectra for a random sample of galaxies within a 0.83 deg(2) region centered on the core of the Centaurus Cluster. Radial velocities were obtained for 225 galaxies to limiting magnitudes of V < 19.5. Of the galaxies for which velocities were obtained, we find 35% to be member galaxies. New redshifts are obtained for 15 Centaurus Cluster members, many of them dwarf galaxies. Radial velocities for the other members agree well with those from previous studies. Of the 78 member galaxies, magnitudes range over 11.8 < V < 18.5 (-21.6 < M-V < -14.9 for H-0 = 70 km s(-1) Mpc(-1)), with a limiting central surface brightness of mu(0) < 22.5 mag arcsec(-2). While many of these galaxies are giants, about 25 galaxies with M-V > -17.0 are considered dwarfs. We constructed the cluster galaxy luminosity function (LF) by using these spectroscopic results to calculate the expected fraction of cluster members in each magnitude bin. The faint-end slope of the LF using this method is shallower than the one obtained using a statistical method to correct for background galaxy contamination. We also use the spectroscopy results to define surface brightness criteria to establish membership for the full sample. Using these criteria, we find a LF very similar to the one constructed with the statistical background correction. For both, we find a faint-end slope alpha similar to - 1.4. The error in faint-end slope for the statistically corrected LF is similar to +/- 0.2. Adjusting the surface brightness membership criteria, we find that the data are consistent with a faint-end slope as shallow as -1.22 or as steep as -1.50. We describe in this paper some of the limitations of using these methods for constructing the galaxy LF. This is Paper II in our investigation of the cluster galaxy LF.