Morphological Butcher-Oemler Effect in the SDSS "Cut and Enhance" Galaxy Cluster Catalog

We investigated the evolution of the fractions of late-type cluster galaxies as a function of redshift using one of the largest, most uniform cluster samples available. The sample consisted of 514 clusters of galaxies in the range of 0.02 ≤ z ≤ 0.3 from the Sloan Digital Sky Survey "Cut and Enhance" galaxy cluster catalog. This catalog was created using a single automated cluster-finding algorithm applied to uniform data from a single telescope, with accurate CCD photometry, thus minimizing the selection biases. We used four independent methods to analyze the evolution of the late-type galaxy fraction. Specifically, we selected late-type galaxies based on each of the rest-frame g - r color, the u - r color, galaxy profile fitting, and the concentration index. The first criterion corresponds to that used in classical Butcher-Oemler analyses. The last two criteria are more sensitive to the morphological type of galaxies. In all four cases, we find an increase in the fraction of late-type galaxies with increasing redshift, significant at the 99.9% level. The results confirm that cluster galaxies do change colors with redshift (the Butcher-Oemler effect) and, in addition, they change their morphology to later-type toward a higher redshift - indicating a morphological equivalence of the Butcher-Oemler effect. We also found a tendency of richer clusters to have lower fractions of late-type galaxies. This trend is consistent with a ram-pressure stripping model, where galaxies in richer clusters are affected by stronger ram pressure due to the higher temperature of clusters.