Narrow Band Continuum Colors of Distant Cluster Populations

Abstract

In this poster, we present new results on narrow band photometry for A2218 ($z$=0.18) and A2125 ($z$=0.25), two clusters with similar redshifts, but very different cluster properties. A2218 is a dense, elliptical-rich cluster (Bautz-Morgan type II) similar to Coma in its evolutionary appearance. A2125 is a less dense, more open cluster (Bautz-Morgan type II-III), although similar in richness. The color-magnitude relation indicates that A2125 has a more developed blue population than A2218 (the Butcher-Oemler effect), although both clusters have significant numbers of blue galaxies (normal star-forming or starburst) compared to a present-day cluster. The red population are identical in A2125 and A2218 and well fit by passive evolution models.