# Neutral hydrogen gas within and around NGC 1316

## TL;DR

This study uses MeerKAT observations to reveal extensive neutral hydrogen gas in NGC 1316, showing large-scale HI tails from a past gas-rich merger that influenced its current structure and star formation activity.

## Contribution

First detection of large-scale HI tails in NGC 1316, linking them to a past gas-rich merger and providing insights into galaxy evolution post-merger.

## Key findings

- HI tails extend 70-150 kpc from the galaxy
- HI mass in tails exceeds previous measurements
- Merger likely occurred 1-3 Gyr ago with a 10:1 mass ratio

## Abstract

We present MeerKAT observations of neutral hydrogen gas (HI) in the nearby merger remnant NGC 1316 (Fornax A), the brightest member of a galaxy group which is falling into the Fornax cluster. We find HI on a variety of scales, from the galaxy centre to its large-scale environment. For the first time we detect HI at large radii (70 - 150 kpc in projection), mostly distributed on two long tails associated with the galaxy. Gas in the tails dominates the HI mass of NGC 1316: 7e+8 Msun -- 14 times more than in previous observations. The total HI mass is comparable to the amount of neutral gas found inside the stellar body, mostly in molecular form. The HI tails are associated with faint optical tidal features thought to be the remnant of a galaxy merger occurred a few billion years ago. They demonstrate that the merger was gas-rich. During the merger, tidal forces pulled some gas and stars out to large radii, where we now detect them in the form of optical tails and, thanks to our new data, HI tails; while torques caused the remaining gas to flow towards the centre of the remnant, where it was converted into molecular gas and fuelled the starburst revealed by the galaxy's stellar populations. Several of the observed properties of NGC 1316 can be reproduced by a ~ 10:1 merger between a dominant, gas-poor early-type galaxy and a smaller, gas-rich spiral occurred 1 - 3 Gyr ago, likely followed by subsequent accretion of satellite galaxies.