| 6th of February 2024 |
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| A Galactic Eclipse: The SMC is Forming Stars in Two, Superimposed Systems |
| by Murray et al. |
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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 from the Gaia and APOGEE
(Apache Point Observatory Galactic Evolution Experiment) surveys
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 figure above is a cartoon schematic of the differential extinction estimation process. In the top plot, the average extinction (determined from the optical/infrared Gaia and APOGEE data) towards stars with "low velocity" is less than the average extinction towards stars with "high velocity", therefore the "low velocity" gas component is in front of the high velocity component in this direction. In the bottom plot, the average extinction towards stars with "low velocity" is greater than the average extinction towards stars with "high velocity", therefore, the "low velocity" gas component is behind the high velocity component in this direction. |