2019MNRAS.487.4856M

We present Atacama Large Millimeter/submillimeter Array (ALMA) CO(J = 2-1) observations of two main-sequence star-forming galaxies at z ∼ 1.47 taken from the High-Z Emission Line Survey (HiZELS). These two systems have been previously reported to be molecular gas-rich f_ H₂ ≡M_ H₂/(M_ H₂ + M_*)∼_0.8. We carried out a follow-up study to resolve, at ∼kpc-scales, the CO emission. These new observations are combined with our earlier ALMA observations (sensitive to diffuse CO emission) and compared with our previous H α-based study at matched spatial resolution. One target is marginally resolved in CO(2-1), showing complex dynamics with respect to the ionized gas traced by H α. While the other source is spatially resolved, enabling a detailed exploration of its internal dynamical properties. In this system, both gaseous phases show similar spatial extension, rotation velocities, and velocity dispersions (V_rot ∼ σ_v ∼ 100 km s^–1) suggesting a rotational velocity to velocity dispersion ratio consistent with unity. By comparing the ionized and molecular gas tracers through the use of a two-dimensional kinematic model, we estimate a median depletion time τ_dep = 2.3 ± 1.2 Gyr for the galaxy as a whole. This value is in agreement with the average τ_dep value observed in local star-forming galaxies at similar spatial scales. Using a thick-disc dynamical modelling, we derive a dynamical mass M_dyn = (1.59 ± 0.19) x 10¹¹ M_☉ within ≃6 kpc. This suggests a dark matter fraction (f_DM ≡ M_DM/M_dyn of 0.59 ± 0.10), in agreement with the average f_DM value derived from stacked rotation curve analysis of galaxies at similar redshift range.