Evolution of the Colour--Radius Relation and the Morphology--Radius Relation in the SDSS Galaxy Clusters

Abstract

We have investigated the redshift evolution of the colour--cluster-centric-radius relation and the morphology--cluster-centric-radius relation in three redshift bins, $0.02\leq z\leq 0.14$, $0.14< z\leq 0.20$, and $0.20< z\leq 0.30$ using a homogeneous sample of 736 galaxy clusters selected from the Sloan Digital Sky Survey. Both the relations are well-defined in all the redshift bins; the fraction of blue/late-type galaxies increases toward outside of clusters.Blue/late-type galaxy fractions are found to decrease with decreasing redshift at any cluster-centric radius. The trend is consistent with the Butcher-Oemler effect and the morphological Butcher-Oemlereffect. In addition, we find that colour (spectral) evolution is almost completed by $z\sim0.2$, whereas morphological evolution continues to the present day. The colour-radius relation is smooth inall the redshift bins, while the morphology--radius relation has a break only in the highest redshift bin. It is also found thatfractions of blue-late type galaxies decreases mostly between the highest and the intermediate redshift bins, while fractions of red-late type galaxies continuously decreases with decreasing redshift through all the redshift bins. These results are consistent with the interpretation that the timescale of the colour (spectral) evolution is shorter than that of the morphological evolution. It is suggested that red-late type galaxies in the middle of the transformation are observed as passive spiral galaxies.