Galaxy Peculiar Velocities and Infall onto Groups

M. L. CECCARELLI; C. VALOTTO; D. G. LAMBAS; N. PADILLA; R. GIOVANELLI; M. HAYNES

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Año: 2005 vol. 622 p. 853 - 861

0004-637X

We  perform  statistical analyses 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  virial mass ($M_{V}$) and  luminosity of group member galaxies ($L_{g}$). Groups with $M_{V} < 10^{13}$ M$_{odot}$ show infall velocities $V_{infall} simeq 150$ km s$^{-1}$ whereas for  $M_{V} > 10^{13}$ M$_{odot}$ a larger infall is observed,  $V_{infall} simeq  200$ km s$^{-1}$. Similarly, we find that galaxies surrounding groups 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 infall can be as large as $V_{infall} simeq 250$ 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 $delta sim 1$ at $rsim 10 h^{-1}Mpc$.