2025PASJ...77..432U

In the present-day universe, the most massive galaxies are ellipticals located in the cores of galaxy clusters, harboring the heaviest super-massive 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 $V_{\rm rot}=530\pm 10$ km s$^{-1}$ and diameter $>$30 kpc. The high specific stellar angular momentum of this system, $j_*=3400\pm 600$ 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.