Morphologically-Identified Merging Galaxies in the SWIRE Fields

TL;DR

This study analyzes over 400 morphologically identified merging galaxies from the SWIRE survey, revealing how their star formation efficiency varies with separation, luminosity contrast, and environment, highlighting environmental impacts on galaxy evolution.

Contribution

It provides new insights into the environmental and evolutionary effects on star formation efficiency in merging galaxies using a large, morphologically selected sample with IR data.

Findings

Anti-correlation between SSFR and galaxy separation.

Most mergers show enhanced star formation, but extremely high SFRs are rare.

Gas-rich mergers have reduced SSFR in cluster environments.

Abstract

We investigate the evolutional and environmental effects on star formation efficiency for more than 400 merging galaxies. The ~400 merging systems, with photometric redshifts smaller than 0.7, are obtained from a catalog of ~15000 morphologically identified merging galaxies derived from observations of the Canada-France-Hawaii Telescope. We also obtained the IR data of the merging galaxies from the Spitzer Wide-area InfraRed Extragalactic Survey (SWIRE). The redshift differences \Delta z between the member galaxies of these merging pairs show a large distribution with 0 < \Delta z < 0.4. We divide our merging pairs into two sub-samples with \Delta z < 0.05 and > 0.05 for further analyses. We find a statistically significant anti-correlation between the specific star formation rate (SSFR) and the separation of the merging galaxies for both sub-samples. Our analyses also show that although most of the merging systems do have enhanced star formation activity, only very rare ones display extremely high SFRs. Additionally, the SSFR of the merging galaxies also decreases when the magnitude difference between two member galaxies becomes large. However, we find that for the merging pairs with large luminosity contrast, the fainter components show higher SSFR than the brighter ones. Finally, there is a higher fraction of gas-poor mergers in galaxy clusters, and the SSFR of gas-rich mergers is reduced in cluster environments.