The Halpha Luminosity Function of the Galaxy Cluster Abell 521 at z = 0.25

Abstract

We present an optical multicolor-imaging study of the galaxy cluster Abell 521 at $z=0.25$, using Suprime-Cam on the Subaru Telescope, covering an area of $32\times 20$ arcmin${}^2$ ($9.4\times 5.8h_{50}^{-2}$ Mpc${}^2$ at $z=0.25$). Our imaging data taken with both a narrow-band filter, $NB816$ (${\lambda }_0=8150$Åand $\Delta \lambda =120$Å), and broad-band filters, $B,V,R_{\mathrm{C}},i^{\prime }$, and $z^{\prime }$ allow us to find 165 H$\alpha$ emitters. We obtain the H$\alpha$ luminosity function (LF) for the cluster galaxies within 2 Mpc; the Schechter parameters are $\alpha =-0.75\pm 0.23$, ${\varphi }^{\star }=10^{-0.25\pm 0.20}$ Mpc${}^{-3}$, and $L^{\star }=10^{42.03\pm 0.17}$ erg s${}^{-1}$. Although the faint end slope, $\alpha$, is consistent with that of the local cluster H$\alpha$ LFs, the characteristic luminosity, $L^{\star }$, is about 6 times (or $\approx 2$ mag) brighter. This strong evolution implies that Abell 521 contains more active star-forming galaxies than the local clusters, being consistent with the observed Butcher-Oemler effect. However, the bright $L^{\star }$ of Abell 521 may be, at least in part, due to the dynamical condition of this cluster.

21 pages, 7 figures, ApJ, Part 1, in press