Cold HI ejected into the Magellanic Stream

TL;DR

This paper reports the first direct detection of cold HI gas in a cloud ejected from the Small Magellanic Cloud, suggesting super shells as a source of cold gas for the Magellanic Stream.

Contribution

It provides the second direct detection of cold HI in the Magellanic Stream using absorption, with detailed temperature measurements and implications for gas ejection mechanisms.

Findings

Detected cold HI with a temperature of 68 ± 20 K.

Identified a cloud ejected from the SMC as part of a fragmented shell.

Proposed super shells as a source of cold gas for the Magellanic Stream.

Abstract

We report the direct detection of cold HI gas in a cloud ejected from the Small Magellanic Cloud (SMC) towards the Magellanic Stream. The cloud is part of a fragmented shell of HI gas on the outskirts of the SMC. This is the second direct detection of cold HI associated with the Magellanic Stream using absorption. The cold gas was detected using 21-cm HI absorption-line observations with the Australia Telescope Compact Array (ATCA) towards the extra-galactic source PMN J0029$-$7228. We find a spin (excitation) temperature for the gas of $68 \pm 20$ K. We suggest that breaking super shells from the Magellanic Clouds may be a source of cold gas to supply the rest of the Magellanic Stream.