An international team of astronomers, using the advanced capabilities of the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), has made significant strides in understanding the structure and evolution of the distant galaxy ADF22.A1. This galaxy, located at a redshift of 3.09, offers unique insights into the processes that drive the formation of massive galaxies and their supermassive black holes (SMBHs), providing a rare opportunity to explore the universe only 2 billion years after the Big Bang.
The results of this observational campaign were published on October 29 on the pre-print server arXiv, revealing new insights into the galaxy’s inner structure. ADF22.A1 is a giant barred spiral galaxy residing in the SSA22 proto-cluster, a dense region filled with young galaxies. Previous observations identified it as a dusty star-forming galaxy (DSFG) with a bright but heavily obscured active galactic nucleus (AGN). However, the heavy dust extinction made it difficult to study the galaxy’s detailed structure, particularly its core. To overcome this challenge, Hideki Umehata and his team from Nagoya University, Japan, turned to JWST and ALMA, which allowed them to peer through the dust and reveal the galaxy’s physical properties.
The observations revealed a well-defined spiral-like structure, traced by emissions from the rest-frame optical-to-near-infrared wavelengths. ADF22.A1 was found to have an effective radius of approximately 22,800 light years, comparable to the sizes of galaxies in the local universe. This suggests that the galaxy is undergoing rapid growth within the dense proto-cluster environment, where interactions and mergers between galaxies likely accelerate its expansion.
At the center of ADF22.A1, the team detected a bright, compact dusty core, indicating an active growth phase of a proto-bulge. Unlike some other DSFGs where dust is concentrated in the central regions, ADF22.A1’s dust is distributed throughout the disk. This suggests that the galaxy is not only forming stars in its core but also undergoing active star formation across its entire disk. This widespread star formation is accompanied by significant dust production, pointing to a highly dynamic and evolving system.
By analyzing emission lines of ionized carbon, the astronomers were able to derive the galaxy’s rotation velocity, which they calculated to be about 530 km/s. This is a remarkable finding, as such high rotation speeds are uncommon for galaxies at this early stage of evolution. Additionally, the galaxy exhibits a high specific stellar angular momentum, supporting the idea that ADF22.A1 is a rapidly rotating galaxy.
The fast rotation presents an intriguing puzzle: how did ADF22.A1’s disk spin up so quickly? The researchers suggest that a combination of cold accretion, where gas falls directly into the galaxy, and mergers with other galaxies is the most plausible explanation. These processes would have provided the necessary mass and angular momentum to accelerate the galaxy’s rotation within a relatively short period, just 2 billion years after the Big Bang.
These findings challenge traditional models of galaxy evolution, suggesting that some galaxies in dense proto-cluster regions may evolve more rapidly than previously believed. The discovery that ADF22.A1’s dust is spread across its disk also has important implications for our understanding of star formation and the role of dust in galaxy evolution. The study of galaxies like ADF22.A1 helps astronomers build a more nuanced picture of how massive galaxies and their supermassive black holes evolve over time.