2004ApJ...601..805U

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'x20' (9.4x5.8h^–2₅₀Mpc² 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,R_C,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/Mpc3, and L^*=10^41.86 to 10^42.2 ergs/s. 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.