The clustering evolution of the galaxy distribution

We follow the evolution of the galaxy population in a LCDM cosmology by means of highresolution N-body simulations in which the formation of galaxies and their observable properties are calculated using a semi-analytic model. We display images of the spatial distribution of galaxies in the simulations that illustrate its evolution and provide a qualitative understanding of the processes responsible for the various biases that develop. We consider three specific statistical measures of clustering at z 1 and z 0: the correlation length (in both real and redshift space) of galaxies of different luminosity, the morphology -density relation and the genus curve of the topology of galaxy isodensity surfaces. For galaxies with luminosity below L * , the z 0 correlation length depends very little on the luminosity of the sample, but for brighter galaxies it increases very rapidly, reaching values in excess of 10 h 21 Mpc. The 'accelerated' dynamical evolution experienced by galaxies in rich clusters, which is partly responsible for this effect, also results in a strong morphology -density relation. Remarkably, this relation is already well-established at z 1. The genus curves of the galaxies are significantly different from the genus curves of the dark matter, however this is not a result of genuine topological differences but rather of the sparse sampling of the density field provided by galaxies. The predictions of our model at z 0 will be tested by forthcoming data from the 2dF and Sloan galaxy surveys, and those at z 1 by the DEEP and VIRMOS surveys.

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