Paper detail

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

We combine multi-object spectroscopy from the 2dF and EFOSC2 spectrographs with optical imaging of the inner 30'x30' of A2384 taken with the ESO Wide Field Imager. We carry 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. 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 subcluster to be 1.6:1. In accordance with other cluster studies, we find that a large fraction of the disk galaxies close to the cluster core show no detectable star formation. Probably these are systems which are quenched due to 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. The substructure in the 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 motivated by their position in colour-magnitude space. The occurrence of morphologically distorted galaxies in the cluster core complies with the hypothesis of A2384 representing a post merger system.