The Structure of Halo Gas Around M33

TL;DR

This study maps the neutral hydrogen gas around galaxy M33, revealing numerous unseen gas clouds and a large hydrogen cloud similar to a galaxy disk, challenging existing galaxy formation models.

Contribution

It provides deeper HI observations of M33, discovering new gas clouds and analyzing their properties to better understand galaxy environment and formation.

Findings

22 discrete HI clouds observed, 11 previously undetected

No optically detected counterparts for the clouds

Discovery of a large hydrogen cloud with galaxy-like characteristics

Abstract

Understanding the distribution of gas in and around galaxies is vital for our interpretation of galaxy formation and evolution. As part of the Arecibo Galaxy Environment Survey (AGES) we have observed the neutral hydrogen (HI) gas in and around the nearby Local Group galaxy M33 to a greater depth than previous observations. As part of this project we investigated the absence of optically detected dwarf galaxies in its neighbourhood, which is contrary to predictions of galaxy formation models. We observed 22 discrete clouds, 11 of which were previously undetected and none of which have optically detected counterparts. We find one particularly interesting hydrogen cloud, which has many similar characteristics to hydrogen distributed in the disk of a galaxy. This cloud, if it is at the distance of M33, has a HI mass of around 10^7 Msun and a diameter of 18 kpc, making it larger in size than M33 itself.