WALLABY Pre-Pilot Survey: The effects of angular momentum and environment on the HI gas and star formation properties of galaxies in the Eridanus supergroup

TL;DR

This study uses ASKAP observations to analyze how environment and angular momentum influence the HI gas and star formation in galaxies within the Eridanus supergroup, revealing environmental effects on gas content and star formation.

Contribution

It provides new insights into the $j_b - M_b$ relation and environmental impacts on HI gas and star formation in a merging galaxy supergroup.

Findings

The $j_b - M_b$ relation follows a power law consistent with previous studies.

Galaxies show significant HI deficiency due to environmental processes.

Star formation may be suppressed by environmental effects before cluster entry.

Abstract

We use high-resolution ASKAP observations of galaxies in the Eridanus supergroup to study their HI, angular momentum and star formation properties, as part of the WALLABY pre-pilot survey efforts. The Eridanus supergroup is composed of three sub-groups in the process of merging to form a cluster. The main focus of this study is the Eridanus (or NGC 1395) sub-group. The baryonic specific angular momentum - baryonic mass ($j_{\mathrm{b}} - M_{\mathrm{b}}$) relation for the Eridanus galaxies is observed to be an unbroken power law of the form $j_{\mathrm{b}} \propto M_{\mathrm{b}}^{0.57 \pm 0.05}$, with a scatter of $\sim 0.10 \pm 0.01$ dex, consistent with previous works. We examine the relation between the atomic gas fraction, $f_{\mathrm{atm}}$, and the integrated atomic disc stability parameter $q$ (the $f_{\mathrm{atm}} - q$ relation), and find that the Eridanus galaxies deviate significantly from the relation owing to environmental processes such as tidal interactions and ram-pressure affecting their HI gas. We find that a majority of the Eridanus galaxies are HI deficient compared to normal star-forming galaxies in the field. We also find that the star formation among the Eridanus galaxies may be suppressed owing to their environment, thus hinting at significant levels of pre-processing within the Eridanus sub-group, even before the galaxies have entered a cluster-like environment.