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5th of February 2024
Neutral hydrogen brightness temperature spectra profiles from a grid of spatial bins placed over the Small Magellanic Cloud, typically showing two dominant components.
A Galactic Eclipse: The SMC is Forming Stars in Two, Superimposed Systems
by Murray et al.
The Small Magellanic Cloud (SMC) is an irregular galaxy that is one of the closest neighbours to our Milky Way galaxy. But despite its closeness, the structure and dynamics of the star-forming disk of the SMC have long confounded us. Murray et al. present a new model for the SMC by comparing the kinematics of young, massive stars with the structure of the Inter-Stellar Medium (ISM) traced by high-resolution observations of neutral atomic hydrogen (HI) from the Galactic Australian Square Kilometer Array Pathfinder survey (GASKAP-HI). They identify thousands of young, massive stars with precise radial velocity constraints and match these stars to the ISM structures in which they likely formed. By comparing the average dust extinction towards these stars, they find evidence that the SMC is composed of two structures with distinct stellar and gaseous chemical compositions. In their model the ISM of the SMC is arranged into two, superimposed, star-forming systems with similar gas mass separated by ~5 kilo-parsecs (~16,000 light years) along the line of sight.

The plot above shows the average HI brightness temperature spectra profiles from a grid of spatial bins placed over the SMC. Each panel includes shaded grey envelopes denoting the 16th through 84th percentile of the brightness temperature within each spatial bin. It is apparent that the radial velocity structure of HI emission features multiple, distinct velocity peaks (and typically two dominant components).

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