ALMA and JWST investigate giant disk galaxy’s formation and evolution

European astronomers have used the Atacama Large Millimeter Array (ALMA) and the James Webb Space Telescope (JWST) to observe a recently discovered giant disk galaxy known as ADF22.1. Results of the new observations, published April 8 on the arXiv preprint server, shed more light on the formation and evolution of this galaxy.

A unique laboratory

ADF22.1, also known as ADF22.A1, is a giant disk barred spiral galaxy residing in a proto-cluster known as SSA22 at a redshift of 3.09. It has an effective radius of some 22,800 light years and a stellar mass of about 100 billion solar masses. Previous observations have found that it is a dusty star-forming galaxy (DSFG) hosting an intrinsically bright yet heavily obscured active galactic nucleus (AGN).

Giant disk galaxies with high stellar masses, like ADF22.1, are generally expected to be quiescent, bulge-dominated systems. Given that ADF22.1 is a starburst galaxy, it is perceived by astronomers as a unique laboratory to explore how early universe galaxies and supermassive black holes (SMBHs) accumulate their mass and ultimately evolve into the most massive elliptical galaxies.

Through ALMA/JWST’s eyes

That is why a team of astronomers led by Francesca Rizzo of the University of Groningen in the Netherlands, decided to utilize ALMA and JWST to explore how it assembled and to determine its fate.

“We exploit ALMA and JWST observations to characterize its [ADF22.1’s] dynamics, compare it to local counterparts, and use this information to understand its formation and subsequent evolution,” the researchers wrote in the paper.

Data acquired with ALMA and JWST allowed the team to measure the galaxy’s rotation velocity and velocity dispersion, perform a rotation-curve decomposition, and constrain the mass of the dark-matter halo.

Extreme properties of ADF22.1

The study confirmed that ADF22.1 reaches an exceptionally high outer rotation velocity of about 530 km/s, which was suggested by previous observations, with a flat rotation curve extending from a radius of about 16,000 out to 49,000 light-years.

Performing for the first time a rotation-curve decomposition for a galaxy of this type, the astronomers found that it has a halo mass of 7.94 trillion solar masses, a stellar mass of 270 billion solar masses and a baryonic mass at a level of 520 billion solar masses. Therefore, the galaxy has a stellar-to-halo mass ratio of 0.2, and a baryon-to-halo mass ratio of 0.4 in units of the cosmological baryon fraction, while the stellar and baryonic-to-halo specific angular momentum ratios were determined to be 0.9 and 1.0, respectively.

Formation and fate

According to the authors of the study, all these results indicate that ADF22.1 is structurally indistinguishable from local giant disk galaxies. It suggests that this galaxy was insufficient in early epochs to expel enough gas to halt the growth of the disk. Based on these findings, the researchers assume that the formation of ADF22.1 could be explained by a scenario in which cold gas condenses out of the hot circumgalactic medium, either spontaneously or through a fountain-like cycle driven by supernova (or AGN) feedback, naturally building a massive, extended, high-angular-momentum disk.

Trying to determine the fate of ADF22.1, astronomers suppose that it is likely destined to become an extreme early-type galaxy: either with an unusually high angular momentum or one of the most massive and extended galaxies in the local universe.

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