The VIMOS-VLT Deep Survey -: Luminosity dependence of clustering at z≃1

We investigate the dependence of galaxy clustering on the galaxy intrinsic luminosity at high redshift, using the data from the First Epoch VIMOS-VLT Deep Survey ( VVDS). The size ( 6530 galaxies) and depth ( I-AB < 24) of the survey allows us to measure the projected two-point correlation function of galaxies, w(p)( r(p)), for a set of volume-limited samples up to an effective redshift < z > = 0.9 and median absolute magnitude -19.6 < M-B < -21.3. Fitting w(p)( r(p)) with a single power-law model for the real-space correlation function xi( r) = ( r/r0)(-y) we measure the relationship of the correlation length r(0) and the slope gamma with the sample median luminosity for the first time at such high redshift. Values from our lower-redshift samples ( 0.1 < z < 0.5) are fully consistent with the trend observed by larger local surveys. In our high redshift sample ( 0.5 < z < 1.2), we find that the clustering strength suddenly rises around M-B(*), apparently with a sharper inflection than at low redshifts. Galaxies in the faintest sample ( < MB > = -19.6) have a correlation length r(0) = 2.7(-0.3)(+0.3) h(-1) Mpc, compared to r(0) = 5.0(-1.6)(+1.5) h(-1) Mpc at < MB > = -21.3. The slope of the correlation function is observed to correspondingly steepen significantly from gamma = 1.6(-0.1)(+0.1) to gamma = 2.4(-0.2)(+0.4). This is not observed either by large local surveys or in our lower-redshift samples and seems to imply a significant change in the way luminous galaxies trace dark-matter halos at z similar to 1 with respect to z similar to 0. At our effective median redshift z similar or equal to 0.9 this corresponds to a strong difference of the relative bias, from b/b* < 0.7 for galaxies with L < L* to b/b* similar or equal to 1.4 for galaxies with L > L*.