Quantifying galactic morphological transformations in the cluster environment

TL;DR

This study quantifies how galaxy shapes change in clusters using a physical parameter, revealing that environment influences galaxy morphology differently based on cluster size and galaxy mass.

Contribution

It introduces a dimensionless angular momentum parameter to objectively measure galaxy morphology and analyzes its variation across different cluster environments.

Findings

Median angular momentum decreases towards cluster centers.

Massive galaxies maintain low angular momentum regardless of position.

Cluster environment significantly influences galaxy morphological transformations.

Abstract

We study the effects of the cluster environment on galactic morphology by defining a dimensionless angular momentum parameter $\lambda_{d}$, to obtain a quantitative and objective measure of galaxy type. The use of this physical parameter allows us to take the study of morphological transformations in clusters beyond the measurements of merely qualitative parameters, e.g. S/E ratios, to a more physical footing. To this end, we employ an extensive Sloan Digital Sky Survey sample (Data Release 7), with galaxies associated with Abell galaxy clusters. The sample contains 121 relaxed Abell clusters and over 51,000 individual galaxies, which guarantees a thorough statistical coverage over a wide range of physical parameters. We find that the median $\lambda_{d}$ value tends to decrease as we approach the cluster center, with different dependences according to the mass of the galaxies and the hosting cluster; low and intermediate mass galaxies showing a strong dependence, while massive galaxies seems to show, at all radii, low $\lambda_{d}$ values. By analysing trends in $\lambda_{d}$ as functions of the nearest neighbour environment, clustercentric radius and velocity dispersion of clusters, we can identify clearly the leading physical processes at work. We find that in massive clusters ($\sigma>700$ km/s), the interaction with the cluster central region dominates, whilst in smaller clusters galaxy-galaxy interactions are chiefly responsible for driving galactic morphological transformations.