An 600 pc View of the Strongly Lensed, Massive Main-sequence Galaxy J0901: A Baryon-dominated, Thick Turbulent Rotating Disk with a Clumpy Cold Gas Ring at z = 2.259

We present a high-resolution kinematic study of the massive main-sequence star-forming galaxy (SFG) SDSS J090122.37+181432.3 (J0901) at z = 2.259, using ~0.″36 Atacama Large Millimeter/submillimeter Array CO(3-2) and ~0.″1-0.″5 SINFONI/VLT Hα observations. J0901 is a rare, strongly lensed but otherwise normal massive ( $\mathrm{log}({M}_{\star }/{M}_{\odot })\sim 11$ ) main-sequence SFG, offering a unique opportunity to study a typical massive SFG under the microscope of lensing. Through forward dynamical modeling incorporating lensing deflection, we fit the CO and Hα kinematics in the image plane out to about one disk effective radius (R _e ~ 4 kpc) at an ~600 pc delensed physical resolution along the kinematic major axis. Our results show high intrinsic dispersions of the cold molecular and warm ionized gas (σ _0,mol. ~ 40 km s^-1 and σ _0,ion. ~ 66 km s^-1) that remain constant out to R _e; a moderately low dark matter fraction (f _DM ~ 0.3-0.4) within R _e; and a centrally peaked Toomre Q parameter-agreeing well with the previously established σ ₀ versus z, f _DM versus Σ_baryon, and Q's radial trends using large-sample non-lensed main-sequence SFGs. Our data further reveal a high stellar mass concentration within ~1-2 kpc with little molecular gas, and a clumpy molecular gas ring-like structure at R ~ 2-4 kpc, in line with the inside-out quenching scenario. Our further analysis indicates that J0901 had assembled half of its stellar mass only ~400 Myr before its observed cosmic time, and the cold gas ring and dense central stellar component are consistent with signposts of a recent wet compaction event of a highly turbulent disk found in recent simulations.