The VIMOS-VLT Deep Survey: Evolution in the Halo Occupation Number since
  z $\sim$ 1
  We model the evolution of the mean galaxy occupation of dark-matter halos
over the range $0.1<z<1.3$, using the data from the VIMOS-VLT Deep Survey
(VVDS). 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 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% 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 $\beta = 1.3 \pm 0.30$. This provides evidence for a rapid accretion
phase of massive halos having a present-day mass $M_0 \sim 10^{13.5} h^{-1}
M_\odot$, with a $m > 0.1 M_0$ merger event occuring between redshifts of 0.5
and 1.0. Futhermore, we find that more luminous galaxies are found to occupy
more massive halos irrespectively of the redshift. Finally, the average number
of galaxies per halo shows little increase from redshift z$\sim$ 1.0 to z$\sim$
0.5, with a sharp increase by a factor $\sim$3 from z$\sim$ 0.5 to z$\sim$ 0.1,
likely due to the dynamical friction of subhalos within their host halos.
