Modelling the evolution of galaxy clustering

Measurements of galaxy clustering are now becoming possible over a range of redshifts out to z similar to 3. We use a semi-analytic model of galaxy fo rmation to compute the expected evolution of the galaxy correlation functio n with redshift. We illustrate how the degree of clustering evolution is se nsitive to the details of sample selection. For a fixed apparent magnitude limit, galaxies selected at higher redshifts are located in progressively r arer dark matter haloes, compared with the general population of galaxies i n place at each redshift. As a result these galaxies are highly biased trac ers of the underlying dark matter distribution and exhibit stronger cluster ing than the dark matter. In general, the correlation length measured in co moving units, decreases at first with increasing redshift, before increasin g again at higher redshift. We show that the E-model often used to interpre t the angular correlation function of faint galaxies gives an inadequate de scription df the evolution of clustering, and offers no physical insight in to the clustering process. We compare our predictions with those of a simpl e, popular model in which a one-to-one correspondence between galaxies and dark haloes is assumed. Qualitatively, this model reproduces the correct ev olutionary behaviour at high redshift, but the quantitative results can be significantly in error. Our theoretical expectations are in good agreement with the high redshift clustering data of Carlberg et al. and Postman et al . but are higher than the measurements of Le Fevre et al.