• galaxies: clusters: general


We have investigated the redshift evolution of the colour–clustercentric radius relation and the morphology–clustercentric radius relation in three redshift bins, 0.02 ≤z≤ 0.14, 0.14 < z≤ 0.20 and 0.20 < z≤ 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 the outside of clusters. Blue/late-type galaxy fractions are found to decrease with decreasing redshift at any clustercentric radius. The trend is consistent with the Butcher–Oemler effect and the morphological Butcher–Oemler effect. In addition, we find that colour (spectral) evolution is almost completed by z∼ 0.2, whereas morphological evolution continues to the present day. The colour–radius relation is smooth in all the redshift bins, while the morphology–radius relation has a break only in the highest redshift bin. It is also found that fractions of blue late-type galaxies decrease mostly between the highest and the intermediate-redshift bins, while the fraction of red late-type galaxies continuously decreases with decreasing redshift through all redshift bins. These results are consistent with the interpretation that the time-scale 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.