2018ApJ...854L..24U

We present deep observations of a z = 1.4 massive, star-forming galaxy (SFG) in molecular and ionized gas at comparable spatial resolution (CO 3-2, NOrthern Extended Millimeter Array (NOEMA); Hα, Large Binocular Telescope (LBT)). The kinematic tracers agree well, indicating that both gas phases are subject to the same gravitational potential and physical processes affecting the gas dynamics. We combine the one-dimensional velocity and velocity dispersion profiles in CO and Hα to forward-model the galaxy in a Bayesian framework, combining a thick exponential disk, a bulge, and a dark matter halo. We determine the dynamical support due to baryons and dark matter, and find a dark matter fraction within one effective radius of f_DM(≤ R_e)=0.18_–0.04^+0.06. Our result strengthens the evidence for strong baryon-dominance on galactic scales of massive z ∼ 1-3 SFGs recently found based on ionized gas kinematics alone.