WALLABY pilot survey: Blinded by the light -- discovery of a fourth member in the ESO 179-013 system

TL;DR

This paper reports the discovery of a new member in the ESO 179-013 dwarf galaxy system using ASKAP/WALLABY HI observations, revealing complex gas dynamics and interactions in a nearby collisional ring galaxy.

Contribution

It presents the first detection of an extended HI envelope and a new galaxy member in the ESO 179-013 system, highlighting the effectiveness of blind HI surveys in studying low-mass galaxy groups.

Findings

Discovery of a fourth galaxy member via HI and radio continuum.

Detection of an extended HI envelope around the system.

Identification of complex gas bridges indicating dynamic interactions.

Abstract

We present new ASKAP/WALLABY HI observations of the nearby dwarf galaxy system ESO 179-013 (Kathryn's Wheel), the nearest known collisional ring galaxy, located 10 Mpc away in the Local Void. The system is composed of three previously known dwarf galaxies embedded in a large HI envelope, with a newly discovered fourth member identified through HI and radio continuum emission behind a bright foreground binary. Galaxy D exhibits the highest star formation rate in the group and deviates from the HI mass-diameter relation, suggesting it is a compact, gas-rich dwarf missed due to stellar foreground contamination. The HI data reveal for the first time an extended HI envelope around the whole system, the neutral gas counterpart of the star-forming ring and gas bridges among members, suggesting a more complex interaction history than the previously proposed collisional ring scenario. ESO 179-013 thus provides a rare opportunity to study hierarchical assembly and gas dynamics in underdense environments and demonstrates the power of blind HI surveys in identifying faint members of low-mass compact groups.