Unravelling the Mysteries of the Leo Ring: An Absorption Line Study of an Unusual Gas Cloud

TL;DR

This study uses HST/COS absorption line observations to measure the metallicity of the Leo Ring, providing insights into its origin and contributing to understanding galaxy evolution processes.

Contribution

First direct metallicity measurement of the Leo Ring using absorption lines, informing theories on its origin and role in galaxy evolution.

Findings

Metallicity of the Leo Ring is approximately 10% of solar.

The measured metallicity challenges primordial gas and interaction origin scenarios.

Results suggest a complex origin involving modified interaction or primordial gas processes.

Abstract

Since the 1980's discovery of the large (2x10^9 Msun) intergalactic cloud known as the Leo Ring, this object has been the center of a lively debate about its origin. Determining the origin of this object is still important as we develop a deeper understanding of the accretion and feedback processes that shape galaxy evolution. We present HST/COS observations of three sightlines near the Ring, two of which penetrate the high column density neutral hydrogen gas visible in 21 cm observations of the object. These observations provide the first direct measurement of the metallicity of the gas in the Ring, an important clue to its origins. Our best estimate of the metallicity of the ring is ~10% Zsun, higher than expected for primordial gas but lower than expected from an interaction. We discuss possible modifications to the interaction and primordial gas scenarios that would be consistent with this metallicity measurement.