ADF22-WEB: A giant barred spiral starburst galaxy in the z = 3.1 SSA22 protocluster core

In the present-day universe, the most massive galaxies are ellipticals located in the cores of galaxy clusters, harboring the heaviest supermassive black holes (SMBHs). However, the mechanisms that drive the early growth phase and subsequent transformation of the morphology and kinematics of galaxies remain elusive. Here we report (sub)kiloparsec-scale observations of stars, gas, and dust in ADF22.A1, a bright dusty starburst galaxy at z = 3.1, hosting a heavily obscured active galactic nucleus and residing in a proto-cluster core. ADF22.A1 is a giant spiral galaxy with the kinematics of a rotating disk with rotation velocity V_rot = 530 ± 10 km s⁻¹ and diameter >30 kpc. The high specific stellar angular momentum of this system, j_∗ = 3400 ± 600 kpc km s⁻¹, requires a mechanism to effectively spin-up ADF22.A1, indicating the importance of accretion from the cosmic web to supply both gas and angular momentum to galaxies in their early gas-rich starburst phase. In its inner region, gas flows along dust lanes in a bar connected with the bright dusty core and the estimated mass ratio of the bulge to the SMBH matches the local relation, suggesting that bars are a key mechanism to shape the early co-evolution of these components. Comparison with cosmological simulations shows that ADF22.A1 will likely evolve into a massive elliptical, experiencing a significant reduction in angular momentum associated with subsequent galaxy mergers.