The study explores the circumgalactic medium (CGM), a vast halo of gas surrounding galaxies, which accounts for about 70% of a galaxy's mass, excluding dark matter. For a long time, scientists have had a limited view of this gas, as it was observed through light from distant objects like quasars, offering only narrow insights.
However, new deep imaging techniques have allowed researchers to detect the CGM of a star-bursting galaxy 270 million light years away, capturing an expansive cloud of gas extending 100,000 light years from the galaxy's center. For comparison, the galaxy's visible starlight disc spans just 7,800 light years.
"We found it everywhere we looked, which was really exciting and kind of surprising," said Associate Professor Nikole M. Nielsen, the lead author of the paper, who is affiliated with Swinburne University, ASTRO 3D, and the University of Oklahoma.
The study, involving researchers from institutions such as Swinburne, the University of Texas at Austin, the California Institute of Technology, and Durham University, uncovered that the CGM stretches far beyond the interstellar medium, transitioning into what becomes part of the larger cosmic web.
"We're now seeing where the galaxy's influence stops, the transition where it becomes part of what's surrounding the galaxy, and, eventually, where it joins the wider cosmic web and other galaxies," added Dr. Nielsen. "These are all usually fuzzy boundaries, but in this case, we seem to have found a fairly clear boundary in this galaxy between its interstellar medium and its circumgalactic medium."
The study also revealed changes in the gas composition as it extended from the center of the galaxy into space, with stars ionizing gas inside the galaxy, while other forces heated the CGM.
"In the CGM, the gas is being heated by something other than typical conditions inside galaxies," said Dr. Nielsen. "This likely includes heating from diffuse emissions from collective galaxies in the universe and possibly contributions from shocks."
The research was made possible using the Keck Cosmic Web Imager (KCWI) on the 10-meter Keck telescope in Hawaii, a cutting-edge instrument capable of capturing thousands of spectra simultaneously. This allows for an unprecedented look at the gas halo surrounding galaxies.
"These one-of-a-kind observations require the very dark sky that is only available at the Keck Observatory on Mauna Kea," said Associate Professor Deanne Fisher, one of the study's authors.
Associate Professor Glenn Kacprzak of Swinburne University added, "KCWI has really changed the game on how we can now measure and quantify the diffuse gas around galaxies."
Professor Emma Ryan-Weber, Director of ASTRO 3D, noted that this is the first time scientists have captured a photograph of a galaxy's halo, adding a crucial piece to the puzzle of galaxy evolution. The study sheds light on how galaxies acquire, process, and lose gas over time, as well as how changes in the CGM may influence the behavior of galaxies.
Dr. Nielsen emphasized the importance of understanding the CGM across different types of galaxies to unravel the mystery of galaxy evolution. "We can observe differences in this gas, which might drive the differences within the galaxies themselves, and changes in this reservoir may actually be driving the changes in the galaxy itself," she said.
The study aligns with the mission of ASTRO 3D, focusing on understanding how galaxies build mass over time. "It helps us understand how galaxies build mass over time," commented Professor Ryan-Weber.
The research may also have implications for the interaction between galaxies. "It's highly likely that the CGMs of our own Milky Way and Andromeda are already overlapping and interacting," said Dr. Nielsen.
Research Report:An emission map of the disk-circumgalactic medium transition in starburst IRAS 08339+6517
Related Links
ARC Centre of Excellence for All Sky Astrophysics
Stellar Chemistry, The Universe And All Within It
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