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

TL;DR

This paper investigates the complex substructures and environmental effects influencing the blue galaxy population in galaxy cluster Abell 85, revealing asymmetric distributions and the impact of ram pressure stripping on gas content.

Contribution

It provides a detailed analysis of substructures and blue galaxy distribution in Abell 85, integrating optical, X-ray, and HI data to understand environmental influences.

Findings

Multiple substructures identified within Abell 85.

Asymmetric distribution of blue, gas-rich galaxies, mainly on the eastern side.

Ram pressure stripping likely affects gas removal from infalling galaxies.

Abstract

This series of papers explores the evolution of late-type galaxies in the rich cluster Abell 85. Here, we revisit the complex dynamical state of A 85 by using independent methods. We analyze the redshift distribution towards the cluster out to 40,000 km/s, and determine the mean redshifts of the background clusters A 87 and A 89. We then search for substructures in A 85 by considering the 2-D galaxy distribution for its members and by applying the kinematical 3-D Delta-test to both projected positions and radial velocities. This clearly reveals several substructures that we describe. 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, and connect it with substructures revealed in the optical and X-rays. By matching our sample of bright blue member galaxies with HI detections reported in the literature, we identify gas-rich and gas-poor ones. HI-rich blue galaxies also turn out to be asymmetrically distributed, with most of them projected on the eastern side of the cluster. No blue objects have been detected in HI up to a projected radius of 2 Mpc in this zone. We estimate the ram pressure stripping exerted by the intra-cluster medium as a function of the projected distance from A 85, and quantify how important this mechanism may be in sweeping the gas out of the infalling spirals.