Resolved HI in two ultra-diffuse galaxies from contrasting non-cluster environments

TL;DR

This study presents the first resolved HI observations of two ultra-diffuse galaxies in different environments, revealing their gas properties, signs of tidal interactions, and dark matter dominance, emphasizing the importance of high-resolution HI data.

Contribution

It provides new resolved HI data for two UDGs in contrasting environments, showing tidal features and dark matter dominance, which was previously limited in such studies.

Findings

Both galaxies show signs of recent tidal interactions.

SdI-2 has a very high MHI/M* ratio of 28.9.

Both galaxies are likely dark matter-dominated within their HI radii.

Abstract

We report on the first resolved HI observations of two blue ultra-diffuse galaxies (UDGs)using the Giant Metrewave Radio Telescope (GMRT). These observations add to the sofar limited number of UDGs with resolved HI data. The targets are from contrasting non-cluster environments: UDG-B1 is projected in the outskirts of Hickson Compact Group 25 and Secco-dI-2 (SdI-2) is an isolated UDG. These UDGs also have contrasting effective radii with Re of 3.7 kpc (similar to the Milky Way) and 1.3 kpc respectively. SdI-2 has an unusually large MHI/M* ratio =28.9, confirming a previous single dish HI observation. Both galaxies display HI morphological and kinematic signatures consistent with a recent tidal interaction, which is also supported by observations from other wavelengths, including optical spectroscopy. Within the limits of the observations' resolution, our analysis indicates that SdI-2 is dark matter-dominated within its HI radius and this is also likely to be the case for UDG-B1. Our study highlights the importance of high spatial and spectral resolution HI observations for the study of the dark matter properties of UDGs.