Galaxy peculiar velocities and infall onto groups

We perform statistical analysis to study the infall of galaxies onto groups and clusters in the nearby universe. The study is based on the Updated Zwicky Catalog and Southern Sky Redshift Survey 2 group catalogs and peculiar velocity samples. We find a clear signature of infall of galaxies onto groups over a wide range of scales 5 h(-1) Mpc < r < 30 h(-1) Mpc, with an infall amplitude on the order of a few hundred kilometers per second. We obtain a significant increase in the infall amplitude with group virialmass (M-V) and luminosity of group member galaxies (L-g). Groups with M-V < 10(13) M-circle dot show infall velocities V-inf similar or equal to 150 km s(-1), whereas for M-V > 10(13) M-circle dot a larger infall is observed, V-inf similar or equal to 200 km s(-1). Similarly, we find that galaxies surrounding groups with L-g < 10(15) L-circle dot have V-inf similar or equal to 100 km s(-1), whereas for L-g > 10(15) L-circle dot groups, the amplitude of the galaxy infall can be as large as V-inf similar or equal to 250 km s(-1). The observational results are compared with the results obtained from mock group and galaxy samples constructed from numerical simulations, which include galaxy formation through semianalytical models. We obtain a general agreement between the results from the mock catalogs and the observations. The infall of galaxies onto groups is suitably reproduced in the simulations, and, as in the observations, larger virial mass and luminosity groups exhibit the largest galaxy infall amplitudes. We derive estimates of the integrated mass overdensities associated with groups by applying linear theory to the infall velocities after correcting for the effects of distance uncertainties obtained using the mock catalogs. The resulting overdensities are consistent with a power law with delta similar to 1 at r similar to 10 h(-1) Mpc.