Infall of galaxies onto groups

Abstract

The growth of the structure within the Universe manifests in the form of accretion flows of galaxies onto groups and clusters. Thus, the present-day properties of groups and their member galaxies are influenced by the characteristics of this continuous infall pattern. Several works both theoretical (in numerical simulations) and observational, have studied this process and provided useful steps for a better understanding of galaxy systems and their evolution. Aims. We aim to explore the streaming flow of galaxies onto groups using observational peculiar velocity data. The effects of distance uncertainties are also analyzed, as well as the relation between the infall pattern and the group and environment properties. Methods. This work deals with the analysis of peculiar velocity data and their projection in the direction of group centers, in order to determine the mean galaxy infall flow. We applied this analysis to the galaxies and groups extracted from the Cosmicflows-3 catalog. We also used mock catalogs derived from numerical simulations to explore the effects of distance uncertainties on the derivation of the galaxy velocity flow onto groups. Results. We determine the infalling velocity field onto galaxy groups with cz < 0.033 using peculiar velocity data. We measured the mean infall velocity onto group samples of different mass ranges, and also explored the impact of the environment where the group resides. Far beyond the group virial radius, the surrounding large-scale galaxy overdensity may impose additional infalling streaming amplitudes in the range of 200-400 km s-1. Also, we find that groups in samples with a well-controlled galaxy density environment show an infalling velocity amplitude that increases with group mass, consistent with the predictions of the linear model. These results from observational data are in excellent agreement with those derived from the mock catalogs.