  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 arcsec ALMA CO(3-2) and 0.1-0.5 arcsec SINFONI/VLT H-alpha observations.
J0901 is a rare, strongly-lensed but otherwise normal massive
(log(M_star/M_sun)~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 H-alpha
kinematics in the image plane out to about one disk effective radius (R_e ~ 4
kpc) at a ~600pc delensed physical resolution along the kinematic major axis.
Our results show high intrinsic dispersions of the cold molecular and warm
ionized gas (sig0_mol ~ 40 km/s and sig0_ion ~ 66 km/s) that remain constant
out to R_e; a moderately low dark matter fraction (f_DM(R_e) ~ 0.3-0.4) within
R_e; and a centrally-peaked Toomre Q-parameter -- agreeing well with the
previously established sig0 vs. z, f_DM vs. Sig_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 Myrs before its observed cosmic
time, and 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.
