Abell 2384: the galaxy population of a cluster post-merger^⋆

¹ Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria
e-mail: florian.pranger@uibk.ac.at
² Laboratoire Lagrange, UMR 7293, Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France

Received: 1 August 2014
Accepted: 29 August 2014

Abstract

Context. We present a spectrophotometric analysis of the galaxy population in the area of the merging cluster Abell 2384 at z = 0.094.

Aims. We investigate the impact of the complex cluster environment on galaxy properties, such as colour, morphology, and star formation rate.

Methods. We combined multi-object spectroscopy from the 2dF and EFOSC2 spectrographs with optical imaging of the inner 30 × 30 arcmin of A2384 taken with the ESO Wide Field Imager. We carried out a kinematical analysis using the EMMIX algorithm and biweight statistics. We address the possible presence of cluster substructures with the Dressler-Shectman test. Cluster galaxies are investigated with respect to [OII] and Hα equivalent width. Galaxies covered by our optical imaging observations are additionally analysed in terms of colour, star formation rate, and morphological descriptors, such as Gini coefficient and M₂₀ index. We study cluster galaxy properties as a function of clustercentric distance and investigate the distribution of various galaxy types in colour−magnitude and physical space.

Results. The Dressler-Shectman test reveals a substructure in the east of the 2dF field of view. We determine the mass ratio between the northern and southern subclusters to be ≲1.6:1. In accordance with other cluster studies, we find that a large number of the disk galaxies close to the cluster core show no detectable star formation (SF). Probably these are systems that are quenched by ram-pressure stripping. The sample of quenched disks populates the transition area between the blue cloud and the red sequence in colour−magnitude space. We also find a population of morphologically distorted galaxies in the central cluster region.

Conclusions. The substructure east of A2384 might be a group of galaxies falling onto the main cluster. We speculate that our sample of quenched spirals represents an intermediate phase in the ram-pressure-driven transformation of infalling field spirals into cluster S0s. This is justified by their position in colour−magnitude space. The occurrence of morphologically distorted galaxies in the cluster core complies with the hypothesis of Abell 2384 representing a post merger system.