Premature dismissal of high-redshift elliptical galaxies

It has recently been argued that single-collapse high-redshift models for e lliptical galaxy formation can be rejected because they predict large numbe rs of very red galaxies at intermediate redshifts, which are not seen in de ep optical-infrared surveys. We argue, however, that this conclusion is pre mature since, while much effort has been invested in refining the predictio ns of hierarchical CDM models, only very simplistic models have been used t o study the evolution of galaxies in other cosmogonies (e.g. isocurvature m odels),We demonstrate that the use of a more realistic multizone chemo-dyna mical single-collapse model yields colours at intermediate redshifts that a re much bluer than those inferred from the one-zone model, and indeed are c omparable to those predicted by hierarchical merging, despite still allowin g > 90 per cent of the final stellar mass of elliptical galaxies to be form ed in the first Gyr of their evolution. We, therefore, conclude that the on e-zone model should be avoided for prediction of the colours of high-redshi ft galaxies and that the use of realistic multizone models allows the exist ence of ellipticals at high redshift, their dismissal being premature.