From peculiar morphologies to Hubble-type spirals: the relation between galaxy dynamics and morphology in star-forming galaxies at z ∼ 1.5

We present an analysis of the gas dynamics of star–forming galaxies at z ∼ 1.5 using data from the KMOS Galaxy Evolution Survey (KGES). We quantify the morphology of the galaxies using HSTCANDELS imaging parametrically and non-parametrically. We combine the Hα dynamics from KMOS with the high–resolution imaging to derive the relation between stellar mass (M*) and stellar specific angular momentum (j*). We show that high–redshift star–forming galaxies at z ∼ 1.5 follow a power-law trend in specific stellar angular momentum with stellar mass similar to that of local late–type galaxies of the form j* ∝ M0.53±0.10∗⁠. The highest specific angular momentum galaxies are mostly disc–like, although generally, both peculiar morphologies and disc-like systems are found across the sequence of specific angular momentum at a fixed stellar mass. We explore the scatter within the j* – M* plane and its correlation with both the integrated dynamical properties of a galaxy (e.g. velocity dispersion, Toomre Qg, Hα star formation rate surface density ΣSFR) and its parameterised rest-frame UV / optical morphology (e.g. Sersic index, bulge to total ratio, Clumpiness, Asymmetry and Concentration). We establish that the position in the j* – M* plane is strongly correlated with the star-formation surface density and the Clumpiness of the stellar light distribution. Galaxies with peculiar rest-frame UV / optical morphologies have comparable specific angular momentum to disc – dominated galaxies of the same stellar mass, but are clumpier and have higher star-formation rate surface densities. We propose that the peculiar morphologies in high–redshift systems are driven by higher star formation rate surface densities and higher gas fractions leading to a more clumpy inter-stellar medium.