A recent study using the Atacama Large Millimeter/submillimeter Array (ALMA) Telescope has uncovered new insights into galaxy evolution. The research, focused on the Southern Pinwheel Galaxy M83, identified 10 high-velocity clouds of molecular gas moving at velocities distinct from the galaxy's overall rotation. This suggests that these gases, which contribute to star formation, originate from outside the galaxy.
The survey was led by Jin Koda, a professor in the Department of Physics and Astronomy at Stony Brook University. He collaborated with Maki Nagata and Fumi Egusa from the University of Tokyo and an international team of astrophysicists. Their findings are published in The Astrophysical Journal.
Galaxies consist mainly of stars and gas, with gas serving as the raw material for star formation. Without external sources replenishing this gas, it is estimated that a galaxy's existing supply would be depleted within about one billion years, halting star formation. The study's insights into M83's molecular composition shed light on how galaxies might evolve over extensive periods.
Professor Koda’s team is utilizing ALMA data to conduct a comprehensive study of molecular gas in M83. "This galaxy resembles our own Milky Way," said Koda, "therefore findings there may also provide clues into star formation and galaxy evolution in the Milky Way."
Nagata explained their methodology: “We analyzed high-sensitivity molecular gas emission line data obtained by ALMA. This led to the discovery of the 10 high-velocity clouds composed, unusually, of molecular gas.” Koda added that "most of these clouds do not correspond to any known supernova remnants in M83."
Egusa proposed two scenarios for these molecular clouds' existence: they could be accreted from outside or ejected by supernova explosions within M83 before falling back due to gravity. However, Koda noted that "even if they were accelerated by supernova explosions, their kinetic energies are too high to be explained by a single event." Nagata concluded that "these features strongly suggest that many of the observed high-velocity clouds must be flowing into M83 from external sources."
The authors highlight this study as the first systematic investigation of high-velocity molecular clouds in nearby galaxies. They plan to continue researching how molecular gas forms outside galaxies.
The research received partial support from the National Science Foundation (NSF), under grant numbers 2006600 and 2406608.