Cool Gas in the Magellanic Stream

TL;DR

This study reports the first direct detection of cold atomic gas in the Magellanic Stream via 21 cm absorption, revealing its properties and suggesting it is not currently forming stars.

Contribution

First direct detection of cold gas in the Magellanic Stream using 21 cm absorption, providing insights into its temperature and composition.

Findings

Detected two absorption components at specific velocities

Inferred spin temperature of ~70 K for the gas

No associated CO emission or dust detected

Abstract

We present the first direct detection of cold atomic gas in the Magellanic Stream, through 21 cm line absorption toward a background radio source, J0119 - 6809, using the Australia Telescope Compact Array. Two absorption components were identified at heliocentric velocities 218.6 km/s and 227.0 km/s, with optical depths of tau ~ 0.02. The corresponding H I emission region has a column density in excess of 2 x 10^20 cm^{-2}. The inferred spin temperature of the emitting gas is ~70 K. We failed to find cool gas in observations of three other radio continuum sources. Although we have definitively detected cool gas in the Stream, its spin temperature is higher than similar components in the LMC, SMC and Bridge, and its contribution to the total H I density is probably lower. No corresponding 12CO(J = 1 -> 0) or dust appears to be associated with the cool gas, suggesting that the cloud is not forming stars.