Environmental effects on galaxy evolution. II: quantifying the tidal features in NIR-images of the cluster Abell 85

TL;DR

This study uses deep NIR imaging to quantify tidal features in galaxies within Abell 85, revealing the impact of environmental mechanisms like tidal interactions and ram-pressure stripping on galaxy evolution.

Contribution

Introduces a new asymmetry index, alpha_An, to quantify tidal disruptions in NIR images of cluster galaxies, enhancing understanding of environmental effects.

Findings

Detected asymmetries in 10 galaxies, mostly in groups and pairs.

Confirmed tidal mechanisms are affecting some galaxies in Abell 85.

Disproved tidal interactions in highly disrupted jellyfish galaxies, suggesting ram-pressure stripping as the cause.

Abstract

This work is part of a series of papers devoted to investigate the evolution of cluster galaxies during their infall. In the present article we imaged in NIR a selected sample of galaxies through- out the massive cluster Abell 85 (z = 0.055). We obtained (JHK) photometry for 68 objects, reaching 1 mag/arcsec^2 deeper than 2MASS. We use these images to unveil asymmetries in the outskirts of a sample of bright galaxies and develop a new asymmetry index, alpha_An, which allows to quantify the degree of disruption by the relative area occupied by the tidal features on the plane of the sky. We measure the asymmetries for a subsample of 41 large area objects finding clear asymmetries in ten galaxies, most of them being in groups and pairs projected at different clustercentric distances, some of them located beyond R500 . Combining information on the Hi-gas content of blue galaxies and the distribution of sub-structures across Abell 85, with the present NIR asymmetry analysis, we obtain a very powerful tool to confirm that tidal mechanisms are indeed present and are currently affecting a fraction of galaxies in Abell 85. However, when comparing our deep NIR images with UV-blue images of two very disrupted (jellyfish) galaxies in this cluster, we discard the presence of tidal 1 interactions down to our detection limit. Our results suggest that ram-pressure stripping is at the origin of such spectacular disruptions. We conclude that across a complex cluster like Abell 85, environment mechanisms, both gravitational and hydrodynamical, are playing an active role in driving galaxy evolution.