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Centro de Astrofísica da Universidade do Porto

Galaxy evolution in Abell 85: I. Cluster substructure and environmental effects on the blue galaxy population

H. Bravo-Alfaro, C. A. Caretta, C. Lobo, F. Durret, T. C. Scott

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 A85 by  using independent methods. First, we analyze the galaxy redshift distribution towards  A85 in the whole range 0–40,000 km s−1, and determine the mean redshifts of the  background clusters A87 and A89, very close in projection to A85. Then we search for  substructures in A85 by considering the 2-D galaxy distribution of its members  (13,000–20,000 km s−1) and by applying the kinematical 3-D 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 A85 to its farthest substructure in this direction - dubbed  the SE clump. By matching our sample of bright blue member galaxies with HI  detections reported in the literature, we identify gas-rich and gas-poor ones. As  expected, the HI-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 HI up to a projected radius of 2Mpc in this zone. We finally estimate the ram pressure stripping exerted by the intra-cluster medium as a  function of the projected distance from A85, in order to quantify how important this mechanism might be in sweeping the gas out of the infalling spirals.

Keywords
galaxies: evolution – galaxies: clusters: individual: Abell 85, Abell 87

Astronomy and Astrophysics
Volume 495, Page 379
February 2009

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