# Dark Matter and HI in Ultra-Diffuse Galaxy UGC 2162

## TL;DR

This study presents GMRT HI observations of UGC 2162, revealing its extended HI disk, moderate rotation, and dark matter properties, providing insights into its nature and challenging some UDG formation theories.

## Contribution

First detailed HI and dark matter analysis of UGC 2162, linking its properties to dwarf galaxies and constraining formation scenarios.

## Key findings

- UGC 2162 has an extended HI disk with R_HI/R_25 ~ 3.3.
- The galaxy's rotation velocity is ~31 km/s, typical for dwarf galaxies.
- Dark matter halo properties are consistent with dwarf galaxy expectations.

## Abstract

Our GMRT HI observations of the ultra diffuse galaxy (UDG) UGC 2162, projected $\sim$ 300 kpc from the centre of the M77 group, reveal it to a have an extended HI disk (R$_{HI}$/R$_{25}$ $\sim$ 3.3) with a moderate rotational velocity (V$_{rot} \sim$ 31 km/s). This V$_{rot}$ is in line with that of dwarf galaxies with similar HI mass. We estimate an M$_{dyn}$ of $\sim$ 1.14 $\times$ 10$^{9}$ M$_\odot$ within the galaxy's R$_{HI}$ $\sim$ 5.2 kpc. Additionally, our estimates of M$_{200}$ for the galaxy from NFW models are in the range of 5.0 to 8.8 $\times$ 10$^{10}$ M$_\odot$. Comparing UGC 2162 to samples of UDGs with HI detections show it to have amongst the smallest R$_e$ with its M$_{HI}$/M$_{\star}$ being distinctly higher and g -- i colour slightly bluer than typical values in those samples. We also compared HI and dark matter (DM) halo properties of UGC 2162 with dwarf galaxies in the LITTLE THINGS sample and find its DM halo mass and profile are within the range expected for a dwarf galaxy. While we were unable to to determine the origin of the galaxy's present day optical form from our study, its normal HI rotation velocity in relation to its HI mass, HI morphology, environment and dwarf mass DM halo ruled out some of the proposed ultra diffuse galaxy formation scenarios for this galaxy.