By Amit Malewar 5 Dec, 2024
Collected at: https://www.techexplorist.com/direct-observation-spheroid-formation-submillimetre-bright-galaxies/94086/
Galaxies in the present-day Universe are generally classified into two main types: younger, star-forming spiral galaxies (such as the Milky Way) and older elliptical galaxies, which have a central bulge, no longer form stars, and lack significant gas. Despite being composed of ancient stars, the formation of spheroidal galaxies has remained a puzzle for astronomers. However, recent discoveries are beginning to unravel this mystery.
An international team of researchers, including scientists from The University of Tokyo’s Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), has found evidence suggesting that old elliptical galaxies may form through intense star formation in the cores of early galaxies. This groundbreaking discovery provides new insights into the evolution of galaxies from the early Universe and enhances our understanding of their formation processes.
The discovery of the birth sites of giant, elliptical galaxies comes from analyzing data from the Atacama Large Millimeter/Submillimeter Array (ALMA) on over 100 Submillimeter Bright Galaxies (SMGs) from the “Cosmic noon” era when the Universe was between 1.6 and 5.9 billion years old—a period marked by intense star formation.
This study provides the first solid observational evidence that spheroidal galaxies can form directly through intense star formation in the cores of highly luminous starburst galaxies in the early Universe. This breakthrough, made possible by new insights from the submillimeter band, will significantly impact models of galaxy evolution, deepening our understanding of how galaxies form and evolve across the cosmos.
In this study, the team employed a novel technique to statistically analyze the surface brightness distribution of dust emission in the submillimeter band. Their findings revealed that the submillimeter emission in most of the sample galaxies was highly compact, with surface brightness profiles that deviated significantly from those of exponential disks.
This suggests that the submillimeter emission originates from structures that are already spheroid-like. A detailed galaxies’ 3D geometry analysis revealed additional evidence for this spheroidal shape. The modeling showed that the ratio of the shortest to the longest of their three axes was, on average, half, and this ratio increased with spatial compactness.
This indicates that most highly star-forming galaxies are intrinsically spherical rather than disk-shaped. Supported by numerical simulations, the study suggests that the formation of these spheroidal galaxies is driven by the combined effects of cold gas accretion and galaxy interactions—a process likely standard in the early Universe during the formation of many spheroids. This discovery has the potential to redefine our understanding of galaxy formation.
The A3COSMOS and A3GOODSS archival projects made the research possible, which provided a large dataset of galaxies observed with high signal-to-noise ratios, enabling detailed analysis. Future studies, utilizing the wealth of ALMA observations alongside new submillimeter and millimeter observations with higher resolution and sensitivity, will facilitate systematic exploration of cold gas in galaxies, providing deeper insights into galaxy formation processes.
This will provide unprecedented insights into the distribution and kinematics of the materials that fuel star formation. With the powerful capabilities of instruments like Euclid, the James Webb Space Telescope (JWST), and the China Space Station Telescope (CSST), which can map the stellar components of galaxies, a more complete picture of early galaxy formation will emerge. Together, these efforts will deepen our understanding of the Universe’s evolution over time.
Journal Reference:
- Tan, QH., Daddi, E., Magnelli, B. et al. In situ spheroid formation in distant submillimetre-bright galaxies. Nature 636, 69–74 (2024). DOI: 10.1038/s41586-024-08201-6
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