Galaxy Peculiar Velocities and Infall onto Groups

We perform statistical analyses to study the infall of galaxies onto groupsand clusters in the nearby Universe. The study is based on the UZC and SSRS2group catalogs and peculiar velocity samples. We find a clear signature ofinfall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc10^{13} M_{\odot} a larger infall is observed,V_{infall} \simeq 200 km s^{-1}. Similarly, we find that galaxies surroundinggroups with L_{g}<10^{15} L_{\odot} have V_{infall} \simeq 100 km s^{-1},whereas for L_{g}>10^{15} L_{\odot} groups, the amplitude of the galaxy infallcan be as large as V_{infall} \simeq 250 km s^{-1}. The observational resultsare compared with the results obtained from mock group and galaxy samplesconstructed from numerical simulations, which include galaxy formation throughsemianalytical models. We obtain a general agreement between the results fromthe mock catalogs and the observations. The infall of galaxies onto groups issuitably reproduced in the simulations and, as in the observations, largervirial mass and luminosity groups exhibit the largest galaxy infall amplitudes.We derive estimates of the integrated mass overdensities associated with groupsby applying linear theory to the infall velocities after correcting for theeffects of distance uncertainties obtained using the mock catalogs. Theresulting overdensities are consistent with a power law with \delta \sim 1 at r\sim 10 h^{-1}Mpc.Comment: 25 pages, 10 figure