Using the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of astronomers has observed a giant spiral galaxy designated ADF22.A1. Results of the observational campaign, published October 29 on the pre-print server arXiv, provide more insights into its inner structure.
At a redshift of 3.09, ADF22.A1 is a giant barred spiral galaxy residing in a proto-cluster known as SSA22. Previous observations have found that it is a dusty star-forming galaxy (DSFG) hosting an intrinsically bright yet heavily obscured active galactic nucleus (AGN).
ADF22.A1 is perceived as a unique laboratory to explore how the most massive galaxies and supermassive black holes (SMBHs) accumulate their mass and evolve into the most massive elliptical galaxies. However, little is known about the structure and properties of this galaxy due to heavy dust extinction affecting its rest-frame ultraviolet appearance.
A group of astronomers led by Hideki Umehata of Nagoya University in Japan employed JWST and ALMA to investigate ADF22.A1, as these instruments can explore the structure and kinematics of this galaxy.
Observations revealed a spiral-like stellar structure of ADF22.A1 tracing rest-frame optical-to-near-infrared emissions. The galaxy has an effective radius of approximately 22,800 light years, comparable to that of local galaxies, suggesting accelerated size growth in the proto-cluster core.
Furthermore, a bright, compact dusty core at the center of ADF22.A1 indicates an active growth phase of a proto-bulge. The dust continuum is distributed across the disk, suggesting significant star formation and dust production.
By analyzing emission lines of ionized carbon, the researchers derived the rotation velocity of ADF22.A1, calculated to be about 530 km/s, along with a relatively high specific stellar angular momentum.
In conclusion, ADF22.A1 is an unusually fast-rotating, giant spiral galaxy, with cold accretion and mergers proposed as plausible mechanisms for its rapid disk spin-up within two billion years after the Big Bang.