TheU‐Band Galaxy Luminosity Function of Nearby Clusters

Despite the great potential of the U-band galaxy luminosity function (GLF) toconstrain the history of star formation in clusters, to clarify the question ofvariations of the GLF across filter bands, to provide a baseline forcomparisons to high-redshift studies of the cluster GLF, and to estimate thecontribution of bound systems of galaxies to the extragalactic near-UVbackground, determinations have so far been hampered by the generally lowefficiency of detectors in the U-band and by the difficulty of constructingboth deep and wide surveys. In this paper, we present U-band GLFs of threenearby, rich clusters to a limit of M_U=-17.5 (M*_U+2). Our analysis is basedon a combination of separate spectroscopic and R-band and U-band photometricsurveys. For this purpose, we have developed a new maximum-likelihood algorithmfor calculating the luminosity function that is particularly useful forreconstructing the galaxy distribution function in multi-dimensional spaces(e.g., the number of galaxies as a simultaneous function of luminosity indifferent filter bands, surface brightness, star formation rate, morphology,etc.), because it requires no prior assumptions as to the shape of thedistribution function. The composite luminosity function can be described by a Schechter functionwith characteristic magnitude M*_U=-19.82+/-0.27 and faint end slopealpha_U=-1.09+/-0.18. The total U-band GLF is slightly steeper than the R-bandGLF, indicating that cluster galaxies are bluer at fainter magnitudes.Quiescent galaxies dominate the cumulative U-band flux for M_U<-14. Thecontribution of galaxies in nearby clusters to the U-band extragalacticbackground is <1% Gyr^-1 for clusters of masses ~3*10^14 to 2*10^15 M_solar.Comment: 44 pages, 11 figures, accepted for publication in Ap