The Ultraviolet and Infrared Star Formation Rates of Compact Group Galaxies: An Expanded Sample

TL;DR

This study expands the understanding of star formation in compact galaxy groups by analyzing UV and infrared data, revealing a bimodal distribution of specific star formation rates and correlations with group properties.

Contribution

It provides a larger sample analysis of star formation rates in compact groups using UV and IR data, highlighting the bimodal nature of specific star formation rates.

Findings

MIR-active galaxies have higher star formation rates and bluer UV colors.

Star formation rates peak around 1 solar mass per year.

Specific star formation rate distribution is bimodal, distinguishing star-forming and quiescent galaxies.

Abstract

Compact groups of galaxies provide insight into the role of low-mass, dense environments in galaxy evolution because the low velocity dispersions and close proximity of galaxy members result in frequent interactions that take place over extended timescales. We expand the census of star formation in compact group galaxies by \citet{tzanavaris10} and collaborators with Swift UVOT, Spitzer IRAC and MIPS 24 \micron\ photometry of a sample of 183 galaxies in 46 compact groups. After correcting luminosities for the contribution from old stellar populations, we estimate the dust-unobscured star formation rate (SFR$_{\mathrm{UV}}$) using the UVOT uvw2photometry. Similarly, we use the MIPS 24 \micron\ photometry to estimate the component of the SFR that is obscured by dust (SFR$_{\mathrm{IR}}$). We find that galaxies which are MIR-active (MIR-"red"), also have bluer UV colours, higher specific star formation rates, and tend to lie in H~{\sc i}-rich groups, while galaxies that are MIR-inactive (MIR-"blue") have redder UV colours, lower specific star formation rates, and tend to lie in H~{\sc i}-poor groups. We find the SFRs to be continuously distributed with a peak at about 1 M$_{\odot}$ yr$^{-1}$, indicating this might be the most common value in compact groups. In contrast, the specific star formation rate distribution is bimodal, and there is a clear distinction between star-forming and quiescent galaxies. Overall, our results suggest that the specific star formation rate is the best tracer of gas depletion and galaxy evolution in compact groups.