The Hα Luminosity Function of the Galaxy Cluster A521 at z = 0.25

Abstract

We present an optical multicolor-imaging study of the galaxy cluster A521 at z=0.25, using Suprime-Cam on the Subaru Telescope, covering an area of 32'×20' (9.4×5.8h-250 Mpc2 at z=0.25). Our imaging data taken with both a narrowband filter, NB816 (λ0=8150 Å and Δλ=120 Å), and broadband filters, B,V,RC,i', and z', allow us to find 165 Hα emitters. We obtain the Hα luminosity function (LF) for the cluster galaxies within 2 Mpc; the Schechter parameters are α=-0.75+/-0.23, φ*=10-0.45 to 10-0.05 Mpc-3, and L*=1041.86 to 1042.2 ergs s-1. Although the faint-end slope α is consistent with that of the local cluster Hα LFs, the characteristic luminosity L* is about 6 times (or ~2 mag) brighter. This strong evolution implies that A521 contains more active star-forming galaxies than the local clusters, being consistent with the observed Butcher-Oemler effect. However, the bright L* of A521 may be, at least in part, due to the dynamical condition of this cluster. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.