The Galaxy Luminosity Functions down toM~ -10 in the Hydra I Cluster

We study the galaxy population of the Hydra I cluster in the central region and a region about 0.6 Mpc away from its center in the B and R C bands down to M ∼ -10 using Subaru Suprime-Cam photometry. We find that the luminosity function of the entire population has a slightly steeper slope (α ∼ -1.6) in the range of -20 < M < -10 than those reported for other clusters in slightly brighter ranges. The slope appears to be steeper in poorer clusters. The number of faint galaxies ( M > -14) increases in the cluster center, as well as in bright galaxies. The Hydra I cluster is dominated by red dwarfs, and the luminosity function shows a significant upturn at M ∼ -16, as is seen in several other nearby clusters but not in the field. This upturn and the variation in the faint-end slope of the luminosity function may be caused by the cluster environment or the evolution history of individual clusters.