Abstract
We measure the field galaxy luminosity function (LF) as a function of color and redshift from z = 0 to z = 0.5 using galaxies from the Norris Survey of the Corona Borealis Supercluster. The data set consists of 603 field galaxies with 0 < z ? 0.5 and spans a wide range in apparent magnitude (14.0 r 21.5), although our field galaxy LF analysis is limited to 493 galaxies with r ? 20.0 mag. We use the observed g-r colors of the galaxies to compute accurate corrections to the rest BAB and r bands. We find that our local r-band LF, when normalized to counts in high galactic latitude fields, agrees well with the local LF measured in the Las Campanas Redshift Survey. Our BAB-band local LF, however, does not match the bj-band LF from the Stromlo/APM survey, having a normalization 1.6 times higher. We see compelling evidence that the BAB-band field galaxy LF evolves with redshift. The evolution is strongest for the population of star-forming galaxies with [O II] ?3727 rest-frame equivalent widths greater than 10 ?. The population of red, quiescent galaxies shows no sign of evolution to z = 0.5. The evolution of the LF that we observe is consistent with the findings of other faint galaxy redshift surveys. The fraction of galaxies with [O II] emission increases rapidly with redshift, but the fraction of galaxies with strong H? absorption, a signature of a burst of star formation, does not. We thus conclude that the star formation in distant galaxies is primarily long-lived. We also compute the LFs of the Corona Borealis supercluster (z ? 0.07, 419 galaxies with 14.1 ? r ? 20.0 mag) and the Abell 2069 supercluster (z ? 0.11, 318 galaxies with 15.1 ? r ? 20.0 mag). The shapes of the two supercluster luminosity functions are broadly similar to the shape of the local luminosity function. However, there are important differences. Both supercluster LFs have an excess of very bright galaxies. In addition, the characteristic magnitude of the Corona Borealis supercluster LF is roughly half a magnitude brighter than that of the local field galaxy LF, and there is a suggestion of an upturn in the LF for galaxies fainter than M(BAB) ~ -17 + 5 log10 h mag, where h is the Hubble constant in units of 100 km s-1 Mpc-1.
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