The VIMOS VLT deep survey: The evolution of galaxy clustering to z≃2 from first epoch observations

This paper presents the evolution of the clustering of the main population of galaxies from z ≃ 2 to z = 0.2, from the first epoch VIMOS VLT Deep Survey (VVDS), a magnitude limited sample with 17.5 ≤ I_AB ≤ 24. The sample allows a direct estimate of evolution from within the same survey over the time base sampled. We have computed the correlation functions ξ(r_p,π) and w_p(r_p), and the correlation length r₀(z), for the VVDS-02h and VVDS-CDFS fields, for a total of 7155 galaxies in a 0.61 deg² area. We find that the correlation length in this sample slightly increases from z = 0.5 to z = 1.1, with r ₀(z) = 2.2-2.9 h^-1 Mpc (comoving), for galaxies comparable in luminosity to the local 2dFGRS and SDSS samples, indicating that the amplitude of the correlation function was ≃2.5 times lower at z ≃ 1 than observed locally. The correlation length in our lowest redshift bin z = [0.2, 0.5] is r₀ = 2.2 h^-1 Mpc, lower than for any other population at the same redshift, indicating the low clustering of very low luminosity galaxies, 1.5 mag fainter than in the 2dFGRS or SDSS. The correlation length increases to r₀ ∼ 3.6 h^-1 Mpc at higher redshifts z = [1.3, 2.1], as we are observing increasingly brighter galaxies, comparable to galaxies with M_BAB = -20.5 locally. We compare our measurement to the DEEP2 measurements in the range z = [0.7, 1.35] (Coil et al. 2004, ApJ, in press) and find comparable results when applying the same magnitude and color selection criteria as in their survey. The slowly varying clustering of VVDS galaxies as redshift increases is markedly different from the predicted evolution of the clustering of dark matter, indicating that bright galaxies traced higher density peaks when the large scale structures were emerging from the dark matter distribution 9-10 billion years ago, being supporting evidence for a strong evolution of the galaxy vs. dark matter bias.