THE Hα LUMINOSITY FUNCTION OF THE GALAXY CLUSTER A521 AT z = 0.25

摘要

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' x 20' (9.4 x 5.8 h_(50)~(-2) Mpc~2 at z = 0.25). Our imaging data taken with both a narrowband filter, NB816 (λ_0 = 8150 A and Δλ = 120 A), 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) Mpc~(-3), and L* = 10~(41.86) to 10~(42.2) 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.