ar X iv : a st ro - p h / 06 12 12 0 v 1 5 D ec 2 00 6 WITNESSING THE BUILD - UP OF THE COLOUR – DENSITY RELATION

We investigate the redshift and luminosity evolution of the galaxy colour-density relation using the data from the First Epoch VIMOS-VLT Deep Survey (VVDS) on scales of R = 5h −1 Mpc up to redshift z ∼ 1.5. While at lower redshift we confirm the existence of a steep colour-density relation, with the fraction of the reddest(/bluest) galaxies of the same luminosity increasing(/decreasing) as a function of density, this trend progressively disappears in the highest redshift bins investigated.Our results suggest the existence of an epoch (more remote for brighter galaxies) characterized by the absence of the colour-density relation on the R = 5h −1 Mpc scales investigated. The rest frame u * − g ′ colour-magnitude diagram shows a bimodal pattern in both low and high density environments up to redshift z ∼ 1.5. We find that the bimodal distribution is not universal but strongly depends upon environment. Both the colour-density and colour-magnitude-density relations, on the R = 5h −1 Mpc scales, appear to be a transient, cumulative product of genetic and environmental factors that have been operating over at least a period of 9 Gyr. These findings support an evolutionary scenario in which star formation/gas depletion processes are accelerated in more luminous objects and in high density environments: star formation activity is progressively shifting with cosmic time towards lower luminosity galaxies (downsizing), and out of high density environments.