The VIMOS-VLT Deep Survey: The evolution of galaxy clustering per spectral type to z ≃ 1.5

We measure the evolution of clustering for galaxies with different spectral types from 6495 galaxies with 17.5 ≤ I_AB ≤ 24 and measured spectroscopic redshifts in the first epoch VIMOS-VLT Deep Survey (VVDS). We divide our sample into four classes, based on the fit of well-defined galaxy spectral energy distributions on observed multi-color data. We measure the projected correlation function w_p(r_p) and estimate the best-fit parameters for a power-law real-space correlation function ζ(r) = (r/r₀)^-γ. We find the clustering of early-spectral-type galaxies to be markedly stronger than that of late-type galaxies at all redshifts up to z ≃ 1.2. At z ∼ 0.8, early-type galaxies display a correlation length r₀ = 4.8 ± 0.9 h^-1 Mpc, while late types have r₀ = 2.5 ± 0.4 h^-1 Mpc. For the latest class of star-forming blue galaxies, we are able to push our clustering measurement to an effective redshift z ∼ 1.4, for luminous galaxies (M_B(AB) ≃-21). The clustering of these objects increases up to r₀ = 3.42 ± 0.7 h^-1 Mpc for z = [1.2,2.0]. The relative bias between early- and late-type galaxies within our magnitude-limited survey remains approximately constant with b = 1.6 ± 0.3 from z = 0 to z = 1.2. This result is in agrement with the local findings and fairly robust against different way of classifying red and blue galaxies. When compared to the expected linear growth of mass fluctuations, a natural interpretation of these observations is that: (a) the assembly of massive early type galaxies is already mostly complete in the densest dark matter halos at z ± 1; (b) luminous late-type galaxies are located in higher-density, more clustered regions of the Universe at z ± 1.5 than their local low luminous counterpart, indicating that star formation activity is progressively increasing, going back in time, in the higher-density peaks that today are mostly dominated by old galaxies.