Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) CO(J = 2-1) observations of two main-sequence star-forming galaxies at z similar to 1.47 taken from the High-Z Emission Line Survey (HiZELS). These two systems have been previously reported to be molecular gas-rich . We carried out a follow-up study to resolve, at similar to 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 alpha-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 alpha. 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 similar to sigma(v) similar to 100kms(-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 tau(dep) = 2.3 +/- 1.2Gyr for the galaxy as a whole. This value is in agreement with the average tau(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 10(11)M(circle dot) within approximate to 6kpc. This suggests a dark matter fraction (f(DM) equivalent to 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.