An Emission‐Line Search for Star‐forming Dwarf Galaxies toward Abell 851

Abstract

We present deep images of the redshift z \ 0.41 galaxy cluster Abell 851 (Cl 0939]4713) including a narrow bandwidth image of the redshifted [O II] jj3726, 3729 line emission. The [O II] doublet is the most accessible tracer of star formation out to redshifts near unity, and we use it to identify candidates for star-forming galaxies. The galaxies selected lie within a projected clustercentric distance of 2 Mpc and have line-of-sight velocities with respect to the cluster in the range of^1460 km s~1. The sample is complete to magnitude for galaxies with emission-line equivalent widths greater than m 5129 (AB) \ 24.0 about 11 in the observed frame. The sample is contaminated by foreground galaxies with a steep 4000 A break across the Ðlters and possibly Lya emitters at z \ 3.31, but such galaxies can be identiÐed using A color, brightness, and equivalent-width criteria. Excluding the likely interlopers, the number density of star-forming galaxies near Cl 0939]4713 is still at least 3È4 times higher than that of a similar column through the Ðeld at z \ 0.4. Galaxies in the cluster sample have lower [O II] equivalent widths than similarly selected Ðeld galaxies at z D 0.4, however, and we suggest that while the density of galaxies is higher in the cluster the star formation activity in individual galaxies is suppressed relative to their counterparts in the Ðeld. The relatively small enhancement in the surface density of the [O II]-selected population toward the cluster core leads us to believe the [O II]-selected galaxies reside in the outer regions of the cluster. We identify a population of starburst galaxies among the [O II] emitters based on their blue g[i color. The majority of the [O II]-selected galaxies appear to be related to the normal spiral galaxy population, but the bursting population is dominated by intrinsically faint galaxies of below average size. We suggest that this population is composed primarily of dwarf galaxies and discuss their relation to the dwarf galaxies in present-day clusters.

An Hα survey of the rich cluster A 1689

“…Thus the total amount of ongoing star formation in this cluster is much less than in the field, as found in most, if not all, high‐density environments (e.g. Balogh et al 1997; Poggianti et al 1999; Martin et al 2000, Paper1).…”

“…There is an increasing body of observational evidence that star formation in the cores of galaxy clusters is much lower than that in the surrounding field, whatever the redshift (e.g. Balogh et al 1997, 1998; Poggianti et al 1999; Martin, Lotz & Ferguson 2000; Couch et al 2001, hereafter Paper I). Although there is evidence that higher redshift clusters have a larger population of late‐type, current or recently star‐forming galaxies than local clusters (e.g.…”

XMM observation of the dynamically young galaxy cluster CL 0939+4713

“…It was extensively observed in morphological and spectroscopic studies of the galaxy population. These studies are based on ground-based optical and near-infrared (Dressler & Gunn 1992;Belloni et al 1995;Fukugita et al 1995;Stanford et al 1995;Belloni & Röser 1996;Dressler et al 1999;Poggianti et al 1999;Iye et al 2000;Martin et al 2000) and HST observations (Dressler et al 1993(Dressler et al , 1994Smail et al 1999;Ziegler et al 1999;Ferreras & Silk 2000) as well as observations in UV (Buson et al 2000) and sub-millimeter (Cowie et al 2002) wavelengths. A high number of star-burst and post-starburst galaxies was found in this distant cluster.…”

The star formation activity from the centers to the outskirts in intermediate redshift clusters

“…More recently, Sato & Martin (2006a,b) made spectroscopic observation of the sample of Martin et al (2000) and were able to confirm many of previous detected emitters as cluster members. But since they focused in studying the previously detected [O ] emitters and their properties, the comparison is not straightforward.…”

“…, Couch et al (2001), Kodama et al (2004), Umeda et al (2004) and Finn et al (2005) have all studied the star formation activity in clusters between 0.2 < z < 0.8 by using narrow-band filters centered in the Hα emission line. Similarly, Martin et al (2000) used a narrow band filter centered in the [O ] emission line in a cluster at z ∼ 0.4. Those studies are varying in depth and spatial coverage, but have the advantage of being complete over the flux limit.…”