The VIMOS-VLT deep survey: Evolution in the halo occupation number since z similar to 1

We model the evolution of the mean galaxy occupation of dark matter haloes over the range 0.1 < z < 1.3, using the data from the VIMOS-VLT Deep Survey. The galaxy projected correlation function w(p)(r(p)) was computed for a set of luminosity-limited subsamples and fits to its shape were obtained using two variants of halo occupation distribution (HOD) models. These provide us with a set of best-fitting parameters, from which we obtain the average mass of a halo and average number of galaxies per halo. We find that after accounting for the evolution in luminosity and assuming that we are largely following the same population, the underlying dark matter halo shows a growth in mass with decreasing redshift as expected in a hierarchical structure formation scenario. Using two different HOD models, we see that the halo mass grows by 90 per cent over the redshift interval z = [0.5, 1.0]. This is the first time the evolution in halo mass at high redshifts has been obtained from a single data survey and it follows the simple form seen in N-body simulations with M(z) = M(0)e(-beta z) , and beta = 1.3 +/- 0.30. This provides evidence for a rapid accretion phase of massive haloes having a present-day mass M(0) similar to 10(13.5) h(-1) M(circle dot), with a m > 0.1 M(0) merger event occurring between redshifts of 0.5 and 1.0. Furthermore, we find that more luminous galaxies are found to occupy more massive haloes irrespective of the redshift. Finally, the average number of galaxies per halo shows little increase from redshift z similar to 1.0 to similar to 0.5, with a sharp increase by a factor of similar to 3 from z similar to 0.5 to similar to 0.1, likely due to the dynamical friction of subhaloes within their host haloes.