Star-forming galaxies in low-redshift clusters: Effects of environment on the concentration of star formation

TL;DR

This study investigates how the cluster environment influences star formation in disk galaxies by analyzing radial distributions and developing new diagnostic tools to identify different environmental effects.

Contribution

It introduces novel indicators and diagnostic diagrams to differentiate between processes like gas stripping, depletion, and starburst activity in cluster galaxies.

Findings

Cluster environment affects star formation distribution.

Early-type disk galaxies show enhanced and concentrated star formation.

Evidence of outer disk star formation truncation in some cluster galaxies.

Abstract

We attempt to determine the dominant processes acting on star-forming disk galaxies as a result of the cluster environment by studying the normalised rates and radial distributions of star formation in galaxies within low-redshift clusters. We develop indicators of different processes based on the radial concentrations of R-band and H alpha light within each of the galaxies studied. The tests are applied to galaxies in each of 3 environments - cluster, supercluster (outside the cluster virial radius) and field. We develop new diagnostic diagrams combining star-formation rate and spatial distribution information to differentiate between stripping of outer disk gas, general gas depletion, nuclear starbursts and galaxy-wide enhancement of star formation. Hubble type classifications of cluster galaxies are found to correlate only weakly with their concentration indices, whereas this correlation is strong for non-cluster populations of disk galaxies. We identify a population of early-type disk galaxies in the cluster population with both enhanced and centrally-concentrated star formation compared to their field counterparts. The enhanced cluster galaxies frequently show evidence of disturbance. A small but non-negligible population of cluster galaxies with truncation of star formation in their outer disks is also found.