An HI study of the collisional ring galaxy NGC 922

TL;DR

This study provides detailed atomic hydrogen observations of the collisional ring galaxy NGC 922, revealing its complex interaction history, extensive HI disc, and high gas fraction, contributing to understanding galaxy collision effects.

Contribution

First detailed HI mapping of NGC 922 showing its complex gas morphology and kinematics, indicating a non-simple interaction history.

Findings

NGC 922 has an extensive HI disc with an HI mass of 1.1×10^{10} M_⊙.

Presence of an 8 kpc HI tail and gas warps in the velocity field.

NGC 922 exhibits a high gas fraction and specific star formation rate.

Abstract

We present new atomic hydrogen (HI) observations of the collisional ring galaxy NGC 922 obtained using the Australia Telescope Compact Array. Our observations reveal for the first time the vast extent of the HI disc of this galaxy. The HI morphology and kinematics of NGC 922 show that this galaxy is not the product of a simple drop-through interaction, but has a more complex interaction history. The integrated HI flux density of NGC 922 from our observations is 24.7 Jy km s$^{-1}$, which is within the error of the flux value obtained using the $64$-m Parkes radio telescope. This flux density translates to a total HI mass of $1.1*10^{10}$ M$_{\circ}$ and corresponds to an HI to total mass fraction (M$_{HI}$/M$_{tot}$) of approximately $0.11$. The gaseous structures of NGC 922 are more extended to the north and include an HI tail that has a projected physical length of $8$ kpc. Gas warps are also evident in the velocity field of NGC 922 and are more prominent on the approaching and the western side of the disc. In comparison with a large sample of star-forming galaxies in the local Universe, NGC 922 possesses a high gas fraction relative to galaxies with a similar stellar mass of ~$10^{10.4}$ M$_{\circ}$, and exhibits a high specific star formation rate.