Recent research utilizing advanced deep imaging techniques has unveiled groundbreaking discoveries about the circumgalactic medium (CGM) of a distant galaxy. This medium, a massive gas halo surrounding galaxies, extends far beyond the visible starlight and plays a vital role in galactic evolution. Scientists now believe that the circumgalactic mediums of the Milky Way and its nearest neighbor, Andromeda, are already overlapping, hinting at complex intergalactic interactions that could reshape our understanding of galaxy dynamics.
The study, published in Nature Astronomy, suggests that this interaction between galaxies begins long before they physically collide. This raises a fundamental question: Where does a galaxy truly end, and where does deep space begin? For decades, this question was challenging to answer due to the limitations of observing gas halos. Researchers could only study the CGM by measuring the light absorbed by background objects like quasars, which provided a narrow, pencil-like beam of data. Now, advanced techniques have allowed scientists to observe these vast halos directly.
In a remarkable leap forward, researchers were able to observe the CGM of a star-bursting galaxy located 270 million light years away. Using deep imaging, they detected glowing gas extending over 100,000 light years into space—far beyond the galaxy’s visible starlight, which stretches just 7,800 light years from its center. These observations revealed significant physical connections of hydrogen and oxygen from the galaxy’s core to its outer reaches. According to lead author Dr. Nikole M. Nielsen, the discovery was surprising as the gas halo was found consistently across every area studied.
This study sheds light on the boundary between a galaxy and the vast cosmos. Dr. Nielsen described this boundary as typically fuzzy, but in the case of the observed galaxy, researchers identified a relatively clear separation between its interstellar medium (the gas within the galaxy) and the circumgalactic medium. In this outer halo, the gas is heated by mechanisms that differ from those within the galaxy, possibly influenced by emissions from other galaxies or cosmic shocks.
This discovery was made possible through the use of the Keck Cosmic Web Imager (KCWI) on the 10-meter Keck telescope in Hawaii. The KCWI allowed researchers to capture thousands of spectra in a single image, offering a detailed view of the gas surrounding galaxies for the first time. With this technology, scientists can now study how galaxies acquire, process, and expel gas, providing key insights into the mysteries of galactic evolution.
The circumgalactic medium plays a crucial role in the cycling of gas, which influences whether a galaxy continues to form stars or transitions into a more dormant state. By understanding the CGM around different types of galaxies, scientists can begin to unravel the processes driving these transitions. Additionally, the study suggests that our Milky Way and Andromeda galaxies are already interacting through their overlapping gas halos, a precursor to a more direct galactic merger in the future. This interaction could offer further clues about how galaxies evolve and impact each other over time.
Source: “An emission map of the disk–circumgalactic medium transition in starburst IRAS 08339+6517” 6 September 2024, Nature Astronomy.
DOI: 10.1038/s41550-024-02365-x
