According to researchers mapping the complex gas dynamics of Stephan’s Quintet, turbulent gas motions in interacting galaxies can actively suppress star formation despite an abundance of raw material. Led by Misaki Yamamoto from the Graduate School of Science at Osaka Metropolitan University, a team published a study in The Astrophysical Journal detailing the first large-scale, spatially resolved molecular gas map of the compact galaxy group using the Atacama Compact Array.
Mapping Molecular Gas in Stephan’s Quintet With the Atacama Compact Array
The research team used the Atacama Compact Array—a subset of the Atacama Large Millimeter/submillimeter Array utilizing a smaller set of radio antennae—to observe carbon monoxide across a 137 kpc by 119 kpc area. Carbon monoxide serves as a reliable proxy for molecular hydrogen, which is notoriously difficult to observe directly despite being the most abundant molecule in star-forming clouds. According to the authors, the resulting map provides a spatially resolved view of the system at roughly 5.5 kpc resolution.
Did you know? Although Stephan’s Quintet appears to be a grouping of five galaxies, only four of them actually form a bound compact group. The fifth member, NGC 7320, is a foreground galaxy situated about seven times closer to Earth than the rest of the system.
How Galactic Collisions Drive Gas Turbulence and Star Formation Diversity
Galaxy interactions subject molecular hydrogen to extreme forces, stretching it into intergalactic streams and compressing it in shock fronts. The study shows that while most molecular gas concentrates in the disk of NGC 7319 and in regions between the galaxies—including a shocked filament and a tidal tail—star formation efficiency varies wildly based on local motion. Regions featuring a small velocity dispersion exhibit star formation efficiencies comparable to nearby disk galaxies, according to the data.
Conversely, regions around the shocked filament with large velocity dispersions between 50 and 150 km per second show strongly suppressed star formation. “Interactions between galaxies can both compress and disperse molecular gas, creating dramatic differences in star formation activity,” lead author Misaki Yamamoto stated in a press release. The findings indicate that violent gas motions prevent clouds from settling and collapsing under their own gravity, choking off new star production even where raw fuel is plentiful.
Tracing Cosmic Evolution Across Time
The distribution of neutral hydrogen and carbon monoxide across Stephan’s Quintet points to an evolved system where gas has been stripped from individual galaxy disks and pushed outward. Along the tidal tail, researchers identified four discrete clumps of carbon monoxide with velocity dispersions of 10 to 30 km per second and masses on the order of 107 to 108 solar masses. Co-author Kazuyuki Muraoka noted that understanding how these collisions enhance or suppress star formation gives astronomers a better tool to trace galaxy evolution across cosmic time.
Frequently Asked Questions
What is Stephan’s Quintet?
Stephan’s Quintet is a well-known visual grouping of five galaxies in the sky, though only four form an interacting compact group while the fifth is a foreground galaxy.
Why do astronomers map carbon monoxide instead of hydrogen?
Molecular hydrogen is difficult to observe directly, so astronomers map carbon monoxide as a trace proxy that responds readily to energy changes in star-forming clouds.
How does turbulence affect star formation in interacting galaxies?
According to researchers at Osaka Metropolitan University, high turbulence prevents molecular gas from settling and collapsing under its own gravity, which suppresses star formation despite abundant gas supplies.
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