Premature dismissal of high-redshift elliptical galaxies

It has recently been argued that single-collapse high-redshift models for elliptical galaxy formation can be rejected because they predict large numbers of very red galaxies at intermediate redshifts, which are not seen in deep optical-infrared surveys. We argue, however, that this conclusion is premature since, while much effort has been invested in refining the predictions of hierarchical CDM models, only very simplistic models have been used to study the evolution of galaxies in other cosmogonies (e.g. isocurvature models). We demonstrate that the use of a more realistic multizone chemo-dynamical single-collapse model yields colours at intermediate redshifts that are much bluer than those inferred from the one-zone model, and indeed are comparable to those predicted by hierarchical merging, despite still allowing > 90 per cent of the final stellar mass of elliptical galaxies to be formed in the first Gyr of their evolution. We, therefore, conclude that the one-zone model should be avoided for prediction of the colours of high-redshift galaxies and that the use of realistic multizone models allows the existence of ellipticals at high redshift, their dismissal being premature.