THE COLOR-MAGNITUDE EFFECT IN EARLY-TYPE CLUSTER GALAXIES

摘要: We present the analysis of color-magnitude relation (CMR) for a sample 57 X-ray-detected Abell clusters within redshift interval 0.02 ? z 0.18. use B - R versus plane to establish that CMR is in all our low-redshift and can be parameterized by single straight line. find CMRs this large cluster different richness types are consistent with having universal properties. The k-corrected colors individual at fixed absolute magnitude have small intrinsic dispersion ~0.05 mag. slope being same clusters, variations entirely accountable filter band shifting effects. determine mean 0.074 mag, rms scatter 0.026 However, modest amount arises from photometric measurement errors possible background superpositions, derived an upper limit. Models explain terms metallicity passive evolution naturally reproduce observed behavior paper. properties models which last episode strong star formation early-type galaxies occurred significantly more than ~3 Gyr ago core set were formed 7 ago. universality provides us important tool detection estimation. A very accurate estimator devised based on apparent color shift due redshift. This calibrator has additional advantage efficient since only two bands needed. An empirically calibrated < 0.20 produces accuracy ?z ~ 0.010. Background typically 0.25 previously unknown, found survey diagrams as secondary red target CMRs. also clear cases X-ray substructure these superpositions. suggests observations subject significant projection contaminations.