Environmental enhancement of loose groups around rich clusters of galaxies

¹ Tartu Observatory, 61602 Tõravere, Estonia
² Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ Tuorla Observatory, Väisäläntie 20, Piikkiö, Finland
⁴ Fermi National Accelerator Laboratory, MS 127, PO Box 500, Batavia, IL 60510, USA

Corresponding author: M. Einasto, maret@aai.ee

Received: 24 January 2002
Accepted: 18 November 2002

Abstract

We have studied the properties of Las Campanas Loose Groups (Tucker et al. 2000) in the neighbourhood of rich (Abell, APM and X-ray) clusters of galaxies. These loose groups show strong evidence of segregation measured in terms of the group richness and the group velocity dispersion: loose groups in the neighbourhood of a rich cluster are typically 2.5 times more massive and 1.6 times more luminous than groups on average, and these loose groups have velocity dispersions 1.3 times larger than groups on average. This is evidence that the large-scale gravitational field causing the formation of rich clusters enhances the evolution of neighbouring poor systems, a phenomenon recently established in numerical simulations of group and cluster formation.