MIGHTEE-HI: Discovery of an HI-rich galaxy group at z = 0.044 with MeerKAT

TL;DR

This paper reports the discovery of a previously unidentified, gas-rich galaxy group at z=0.044 using MeerKAT, highlighting the importance of spatially-resolved HI mapping in understanding galaxy group assembly.

Contribution

First detection of an HI-rich galaxy group at low redshift with detailed spatial and velocity maps, demonstrating MeerKAT's capabilities in environmental studies.

Findings

The group has a dynamical mass of 10^12.32 solar masses.

It exhibits an unusually high HI-to-stellar mass ratio, 0.7 dex above expectations.

The group shows disturbed HI morphologies indicating early assembly stages.

Abstract

We present the serendipitous discovery of a galaxy group in the XMM-LSS field with MIGHTEE Early Science observations. Twenty galaxies are detected in HI in this $z\sim0.044$ group, with a $3\sigma$ column density sensitivity of $N_\mathrm{HI} = 1.6\times10^{20}\,\mathrm{cm}^{-2}$. This group has not been previously identified, despite residing in a well-studied extragalactic legacy field. We present spatially-resolved HI total intensity and velocity maps for each of the objects, which reveal environmental influence through disturbed morphologies. The group has a dynamical mass of $\log_{10}(M_\mathrm{dyn}/\mathrm{M}_\odot) = 12.32$, and is unusually gas-rich, with an HI-to-stellar mass ratio of $\log_{10}(f_\mathrm{HI}^\mathrm{*}) = -0.2$, which is 0.7 dex greater than expected. The group's high HI content, spatial, velocity, and identified galaxy type distributions strongly suggest that it is in the early stages of its assembly. The discovery of this galaxy group is an example of the importance of mapping spatially-resolved HI in a wide range of environments, including galaxy groups. This scientific goal has been dramatically enhanced by the high sensitivity, large field-of-view, and wide instantaneous bandwidth of the MeerKAT telescope.