Galaxy evolution in Abell 85

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.

A study of catalogued nearby galaxy clusters in the SDSS-DR4

“…Ramella et al (2007), using a different approach, detected three main structures in Abell 85. The two substructures (S 1 and S 2 ) detected by Ramella et al (2007) are close to the C2 and SB substructures reported by Bravo-Alfaro et al (2009). Figure 8 shows the substructure in Abell 85 obtained by our method.…”

“…Indeed, at the position of this group of galaxies there are no objects in our data (compare Fig. 4 from Bravo-Alfaro et al 2009;and our Fig. 7).…”

“…Their observations are ∼2 mag deeper than our data. Notice that we have not identified any galaxy from the substructure labeled F in Bravo-Alfaro et al (2009). Indeed, at the position of this group of galaxies there are no objects in our data (compare Fig.…”

“…The galaxies in substructure were selected using δ i,99 (asterisks) or δ g,99 (diamonds). (Ramella et al 2007;Bravo-Alfaro et al 2009), and there are also available X-ray data for this cluster (Durret et al 2003), making this cluster ideal for comparing the substructure obtained by us with other studies. Bravo-Alfaro et al (2009) used the DS test to detect the substructure in Abell 85 and found five prominent regions of substructure.…”

“…The situation is better when the galaxies in substructure are determined by δ i,99 . In this case, for the EC2 sample we obtain two groups of galaxies in substructures that correspond to the main groups of galaxies in substructure (C2 and SE) identified by Bravo-Alfaro et al (2009) in this cluster. That we have not identified the other groups proposed by these authors might be related to the different galaxy population studied.…”