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Astron. Astrophys. 334, 99-109 (1998)

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Evolution of the colour-magnitude relation of early-type galaxies
in distant clusters

Tadayuki Kodama 1, 2, Nobuo Arimoto 2, 4, Amy J. Barger 1, 3 and Alfonso Aragón-Salamanca 1

1 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK (kodama@ast.cam.ac.uk)
2 Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181, Japan
3 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA
4 Observatoire de Paris, Section de Meudon, DAEC, F-92195 Meudon Principle Cedex, France

Received 21 November 1997 / Accepted 17 February 1998


We present a thorough quantitative analysis of the evolution of the colour-magnitude relation for early-type galaxies in 17 distant clusters with redshifts [FORMULA] using the Kodama & Arimoto (1997) evolutionary model for elliptical galaxies. The model is calibrated to reproduce the colour-magnitude relation for Coma ellipticals at [FORMULA] and gives the evolution of the slope and zero-point as a function of redshift. We find no significant differences between the colour-magnitude relations of the clusters in our sample. The slopes can be reproduced by a single model sequence in which all elliptical galaxies are assumed to be equally old (the maximum age difference allowed for the brightest 3 magnitudes is only 1 Gyr) and to have mean stellar metallicities which vary as a function of galaxy luminosity. The zero-points of the colour-magnitude relations constrain the epoch of major star formation in early-type galaxies to [FORMULA] -4. This study provides two important constraints for any model of the formation of rich clusters: the uniformity of the ages of the stellar populations in the early-type galaxies and the universality of the metallicity sequence of these galaxies as a function of galaxy mass.

Key words: galaxies: active – galaxies: elliptical and lenticular, cD – galaxies: evolution – galaxies: formation – galaxies: photometry – galaxies: stellar content

Send offprint requests to: T. Kodama

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© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998