From peculiar morphologies to Hubble-type spirals: the relation between galaxy dynamics and morphology in star-forming galaxies at z similar to 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. We quantify the morphology of the galaxies using HST CANDELS imaging parametrically and non-parametrically. We combine the H α 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, H α star formation rate surface density SFR) and its parametrized 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 interstellar medium.This work was supported by the Science and Technology Facilities Council (ST/L00075X/1). SG acknowledges the support of the Science and Technology Facilities Council through grant ST/N50404X/1 for support. EI acknowledges partial support from FONDECYT through grant N◦ 1171710. We thank the FMOSCOSMOS team for their invaluable contributions to the KGES target selection. ALT acknowledges support from STFC (ST/L00075X/1 and ST/P000541/1), ERC Advanced Grant DUSTYGAL (321334), and a Forrest Research Foundation Fellowship. LC is the recipient of an Australian Research Council Future Fellowship (FT180100066) funded by the Australian Government. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013