The cosmological evolution of colour gradients in spheroids

Abstract

The analysis of the four-colour maps of galaxies in the Hubble Deep Field has revealed in the sample of 0.4<z<1 early-type field galaxies the existence of ellipticals with a predominantly old coeval stellar population. However, there is another, unexpected, category of HDF early-type galaxies, in which the galaxy core is significantly bluer than the outer regions. We demonstrate that these colour gradients are predicted by the multi-zone chemodynamical model for the evolution of elliptical galaxies. We suggest that the colour gradient could be used as a chronometer of the evolution of elliptical galaxies: galaxies younger than a few Gyr exhibit cores bluer than the surrounding galaxy, due to ongoing star formation, while more evolved galaxies have redder cores, due to metallicity gradients increasing towards the centre.

MNRAS accepted, 7 pages, 5 Figures

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