# Constraints on the HI Mass of NGC 1052-DF2

## TL;DR

Deep 21 cm observations of NGC 1052-DF2 reveal an extremely low neutral hydrogen gas content, supporting its classification as a gas-poor galaxy possibly affected by environmental factors or distance uncertainties.

## Contribution

First deep single-dish HI observations of NGC 1052-DF2 providing stringent upper limits on its neutral gas mass and gas fraction.

## Key findings

- NGC 1052-DF2 has an HI mass less than 5.5 x 10^5 M_sun at 19 Mpc
- The galaxy's gas fraction is less than 0.0027, indicating extreme gas deficiency
- If at 13 Mpc, the HI mass limit is even lower, less than 2.5 x 10^5 M_sun

## Abstract

We report deep, single-dish 21 cm observations of NGC 1052-DF2, taken with the Green Bank Telescope. NGC 1052-DF2, proposed to be lacking in dark matter, is currently classified as an ultra-diffuse galaxy in the NGC 1052 group. We do not detect the galaxy, and derive an upper limit on the HI, mass. The galaxy is extremely gas-poor, and we find that a $3\sigma \, M_{HI}$ detection at a distance of 19 Mpc and using a line width of 3.2 km $\rm s^{-1}$ would have an upper limit of $M_{HI,lim} < 5.5 \times 10^5$ M$_{\odot}$. At this mass limit, the gas fraction of neutral gas mass to stellar mass is extremely low, at $M_{HI}$/M$_{*}$ $\, < \, 0.0027$. This extremely low gas fraction, comparable to Galactic dwarf spheroidals and gas-poor dwarf ellipticals, implies that either the galaxy is within the virial radius of NGC1052, where its gas has been stripped due to its proximity to the central galaxy, or that NGC 1052-DF2 is at distance large enough to inhibit detection of its gas. We also estimated the upper limit of the HI mass of NGC 1052-DF2 resided at 13 Mpc. This would give an HI mass of $M_{HI,lim} < 2.5 \times 10^5$ M$_{\odot}$, and an HI gas fraction of $M_{HI}$/M$_{*}$r $\, < \, 0.0012$, becoming even more extreme. While the dark matter fraction would be less extreme at this distance, the neutral gas fraction would be unprecedented for an object in a low density environment.