The Colour–Magnitude Relation of Early-Type Galaxies in the Hubble Deep Field North

We present the rest-frame colour–magnitude diagram for 35 early-type galaxies in the Hubble Deep Field with median redshift 0.9.Although with considerable scatter, a red sequence 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. This revised version was published online in July 2006 with corrections to the Cover Date.