C. López-Sanjuan, O. Cucciati, O. Le Fèvre, L. Tresse, O. Ilbert, C. Adami, S. Bardelli, T. Contini, E. Zucca
We use the VIMOS VLT Deep Survey to study the close environment of galaxies in groups at 0.2 <= z < 0.95. Close neighbours of L_B >= L*_B galaxies (Me_B = M_B + 1.1z <= -20) are identified with Me_B <= -18.25, and within a relative distance 5h^-1 kpc <= rp <= 100h^-1 kpc and relative velocity Delta v <= 500 km/s . The richness N of a group is defined as the number of Me_B <= -18.25 galaxies belonging to that group. We split our main galaxy sample in groups into red/passive (NUV - r >= 4.25) and blue/star-forming (NUV - r < 4.25) samples. We find that blue galaxies with a close companion are located preferentially in poor groups, while the red ones are in rich groups. The number of close neighbours per red galaxy increases with N, with n_red being proportional to 0.11N, while that of blue galaxies does not depend on N and is roughly constant. In addition, these trends are found to be independent of redshift, and only the average n_blue evolves, decreasing with cosmic time. Our results support the following assembly history of L_B >= L*_B galaxies in the group environment: red, massive galaxies were formed in/accreted by the dark matter halo of the group at early times (z >= 1) and hence their number of neighbours provides a fossil record of the stellar mass assembly of groups, traced by their richness N. On the other hand, blue, less massive galaxies have been accreted by the group potential recently and are still in their parent dark matter halo, having the same number of neighbours irrespective of N. As time goes by, these blue galaxies settle in the group potential and turn red/fainter, thus becoming satellite galaxies in the group. With a toy quenching model, we estimate an infall rate of field galaxies into the group environment of R_infall = 0.9 - 1.5 x 10^-4 Mpc^-3 Gyr^-1 at z ~ 0.7.
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http://arxiv.org/abs/1303.1074
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