Galaxy distribution and evolution around a sample of 2dF groups

¹ Laboratório de Astrofísica Teórica e Observacional, Departamento de Ciências Exatas e Tecnológicas, Universidade Estadual de Santa Cruz, 45650-000 Ilhéus-BA, Brazil e-mail: albr@uesc.br e-mail: ana.schilling@gmail.com
² Instituto Astronômico e Geofísico – USP, São Paulo-SP, Brazil e-mail: trevisan@iagusp.usp.br
³ IP&D Universidade do Vale do Paraíba, Av. Shishima Hifumi 2911, São José dos Campos, 12244-000, Brazil e-mail: paal05@gmail.com

Received: 28 May 2009
Accepted: 1 July 2009

Abstract

Context. We study galaxy evolution and spatial patterns in the surroundings of a sample of 2dF groups.

Aims. Our aim is to find evidence of galaxy evolution and clustering out to 10 times the virial radius of the groups and so redefine their properties according to the spatial patterns in the fields and relate them to galaxy evolution.

Methods. Group members and interlopers were redefined after the identification of gaps in the redshift distribution. We then used exploratory spatial statistics based on the the second moment of the Ripley function to probe the anisotropy in the galaxy distribution around the groups.

Results. We found an important anticorrelation between anisotropy around groups and the fraction of early-type galaxies in these fields. Our results illustrate how the dynamical state of galaxy groups can be ascertained by the systematic study of their neighborhoods. This is an important achievement, since the correct estimate of the extent to which galaxies are affected by the group environment and follow large-scale filamentary structure is relevant to understanding the process of galaxy clustering and evolution in the Universe.