The Nature of Star Formation at 24 microns in the Group Environment at 0.3 < z < 0.55

TL;DR

This study investigates star formation in intermediate-redshift galaxy groups and finds that, despite differences in morphology and mass, group galaxies exhibit star-forming properties similar to field galaxies, with environment influencing specific star formation rates.

Contribution

It provides new insights into how galaxy properties in groups compare to those in the field and clusters at 0.3 < z < 0.55, highlighting the role of environment in galaxy evolution.

Findings

Group and field galaxies have different morphology and mass distributions.

Group galaxies show similar star-forming properties to field galaxies of comparable mass and morphology.

Groups contain a significant number of massive, star-forming early-type galaxies.

Abstract

Galaxy star formation rates (SFRs) are sensitive to the local environment; for example, the high-density regions at the cores of dense clusters are known to suppress star formation. It has been suggested that galaxy transformation occurs largely in groups, which are the intermediate step in density between field and cluster environments. In this paper, we use deep MIPS 24 micron observations of intermediate-redshift (0.3 < z < 0.55) group and field galaxies from the Group Environment and Evolution Collaboration (GEEC) subset of the Second Canadian Network for Observational Cosmology (CNOC2) survey to probe the moderate-density environment of groups, wherein the majority of galaxies are found. The completeness limit of our study is log(L_TIR (L_sun)) > 10.5, corresponding to SFR > 2.7 M_sun/yr. We find that the group and field galaxies have different distributions of morphologies and mass. However, individual group galaxies have star-forming properties comparable to those of field galaxies of similar mass and morphology; that is, the group environment does not appear to modify the properties of these galaxies directly. There is a relatively large number of massive early-type group spirals, along with E/S0 galaxies, that are forming stars above our detection limit. These galaxies account for the nearly comparable level of star-forming activity in groups as compared with the field, despite the differences in mass and morphology distributions between the two environments. The distribution of specific SFRs (SFR/M_*) is shifted to lower values in the groups, reflecting the fact that groups contain a higher proportion of massive and less active galaxies. Considering the distributions of morphology, mass, and SFR, the group members appear to lie between field and cluster galaxies in overall properties.