ALMA/ACA CO Survey of the IC 1459 and NGC 4636 Groups: Environmental Effects on the Molecular Gas of Group Galaxies

TL;DR

This study uses ACA CO imaging to examine how the environment in galaxy groups affects the cold gas and star formation in member galaxies, revealing disturbed gas morphologies and suppressed star formation compared to isolated galaxies.

Contribution

First CO imaging survey of loose galaxy groups, providing high-resolution data on molecular and atomic gas distributions in group galaxies.

Findings

Group galaxies show disturbed CO and HI morphologies.

Group galaxies have lower star formation rates than isolated counterparts.

Environmental effects influence cold gas distribution and galaxy evolution.

Abstract

We present new results of a 12CO(J=1-0) imaging survey using the Atacama Compact Array (ACA) for 31 HI detected galaxies in the IC 1459 and NGC 4636 groups. This is the first CO imaging survey for loose galaxy groups. We obtained well-resolved CO data (~0.7-1.5 kpc) for a total of 16 galaxies in two environments. By comparing our ACA CO data with the HI and UV data, we probe the impacts of the group environment on the cold gas components (CO and HI gas) and star formation activity. We find that CO and/or HI morphologies are disturbed in our group members, some of which show highly asymmetric CO distributions (e.g., IC 5264, NGC 7421, and NGC 7418). In comparison with isolated galaxies in the xCOLD GASS sample, our group galaxies tend to have low star formation rates and low H2 gas fractions. Our findings suggest that the group environment can change the distribution of cold gas components, including the molecular gas, and star formation properties of galaxies. This is supporting evidence that preprocessing in the group-like environment can play an important role in galaxy evolution.