Astronomers witness the in situ spheroid formation in distant submillimetre-bright galaxies

Galaxies in the universe today come in all shapes and sizes and can be roughly divided into two categories: younger disk-shaped spiral galaxies, which like our Milky Way are still forming new stars; and older elliptical galaxies, which have mainly central cores. The sphere dominates, no longer forms stars, and is mostly devoid of gas. These globular galaxies contain very old stars, but how they formed remained a mystery—until now.

A paper published today announces the discovery of the birthplace of giant elliptical galaxies nature ——From the Atacama Large Millimeter/submillimeter Array (ALMA) data analysis of more than 100 submillimeter bright galaxies (SMG), its redshift can be traced back to the “cosmic noon” era, when the age of the universe was about 1.6 By 5.9 billion years ago, many galaxies were actively forming stars. This study, based on a new perspective at submillimeter wavelengths, provides the first reliable observational evidence that intense star formation in the cores of highly luminous starburst galaxies in the early universe can directly form spheroids. This breakthrough will greatly impact models of galaxy evolution and deepen our understanding of how galaxies form and evolve in the universe.

In this study, researchers led by Tan Qinghua, associate researcher at the Purple Mountain Observatory of the Chinese Academy of Sciences, and including Kavli IPMU Professor John Silverman, program researcher Boris Kalita, and graduate student Liu Zhaoxuan, conducted a statistical analysis of the surface brightness distribution of dust emissions. bands, combined with novel analysis techniques. They found that the submillimeter emission of most of the sample galaxies is very compact, with surface brightness distributions that differ significantly from that of exponential disks. This suggests that submillimeter emissions typically originate from structures that are already spheroidal. Further evidence for this ellipsoidal shape comes from detailed analysis of the 3D geometry of the galaxy. Modeling based on the high axial ratio distribution shows that the ratio of the shortest axis to the longest axis of the three axes is half on average and increases with increasing spatial compactness. This suggests that most of these highly star-forming galaxies are spherical in nature rather than disk-shaped. Supported by numerical simulations, this discovery shows us that the main mechanism for the formation of these three-dimensional galaxies (spheres) is the simultaneous action of cold gas accretion and galaxy interactions. This process is thought to be quite common in the early universe, the period when most spheres were formed. It could redefine how we understand galaxy formation.

This study was possible thanks to the A3COSMOS and A3GOODSS archive projects, which allowed the researchers to collect a large number of galaxies observed with a high enough signal-to-noise ratio for detailed analysis. Future exploration of the wealth of ALMA observations accumulated over the years, as well as new submillimeter and millimeter observations with higher resolution and sensitivity, will allow us to systematically study cold gas in galaxies. This will provide unprecedented insights into the distribution and kinematics of the raw materials required for star formation. With the powerful mapping capabilities of the Euclid, James Webb Space Telescope (JWST) and China Space Station Telescope (CSST), we will obtain a more complete picture of early galaxy formation. Together, these insights will deepen our understanding of how the entire universe evolves over time.