The colour-magnitude relation of early-type galaxies in the Hubble Deep Field

Abstract

We present the rest-frame colour-magnitude diagram for 35 early-type galaxies in the Hubble Deep Field with median redshift 0.9. Although they have considerable scatter, a red sequence that is well described by the passive evolution of an intrinsically old stellar population is observed. Comparison with the passively evolved colour-magnitude relation of the rich Coma cluster (z=0.023) indicates that at least ~1/2 of the early-type galaxies in the field at this redshift are as old as those in rich clusters.