Galaxy evolution in Abell 85

I. Cluster substructure and environmental effects on the blue galaxy population

¹ Departamento de Astronomía, Universidad de Guanajuato, Apdo. Postal 144, Guanajuato 36000, Mexico e-mail: hector@astro.ugto.mx
² Centro de Astrofísica da Universidade do Porto, Rua das Estrelas 4150-762 Porto, Portugal
³ Depto. de Matemática Aplicada, Faculdade de Ciências, Univ. do Porto, R. do Campo Alegre 687, 4169-007 Porto, Portugal
⁴ Institut d'Astrophysique de Paris, CNRS, UMR 7095, Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁵ Center for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK

Received: 1 August 2008
Accepted: 25 September 2008

Abstract

In this series of papers we explore the evolution of late-type galaxies in the rich cluster Abell 85. In this first paper we revisit the complex dynamical state of A 85 by using independent methods. First, we analyze the galaxy redshift distribution towards A 85 in the whole range 0-40 000  km s^-1, and determine the mean redshifts of the background clusters A 87 and A 89, very close in projection to A 85. Then we search for substructures in A 85 by considering the 2D galaxy distribution of its members (13 000-20 000  km s^-1) and by applying the kinematical 3D Δ-test to both projected positions and radial velocities. This clearly reveals several substructures: one close to the cluster core and three more projected towards the southeast, along the region where an X-ray filament has been extensively studied. We also analyse the distribution of the brightest blue galaxies across a major fraction of the cluster volume, considering if they are gas-rich or poor. We report a very asymmetric distribution of the blue member galaxies, with most of them to the east and southeast, namely in the region joining the core of A 85 to its farthest substructure in this direction – dubbed the SE clump. By matching our sample of bright blue member galaxies with H i detections reported in the literature, we identify gas-rich and gas-poor ones. As expected, the H i-rich blue galaxies follow the same trend as the parent sample, with most of them projected on the eastern side of the cluster as well. Interestingly no blue objects have been detected in H i up to a projected radius of 2 Mpc in this zone. We finally estimate the ram pressure stripping exerted by the intra-cluster medium as a function of the projected distance from A 85, in order to quantify how important this mechanism might be in sweeping the gas out of the infalling spirals.