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

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.

19 pages, 19 figures, accepted for publication in MNRAS