From Peculiar Morphologies to Hubble-type Spirals: The relation between galaxy dynamics and morphology in star-forming galaxies at z~1.5

TL;DR

This study investigates the relationship between galaxy morphology and dynamics at z~1.5, revealing that high-redshift star-forming galaxies follow a similar angular momentum-mass relation as local galaxies, with morphology linked to star formation and clumpiness.

Contribution

It provides new insights into how galaxy morphology and angular momentum relate at high redshift, highlighting the role of star formation surface density and clumpiness in galaxy evolution.

Findings

High-redshift galaxies follow a j* ∝ M*^0.53 relation similar to local galaxies.

Peculiar morphologies are associated with higher star formation surface densities and clumpiness.

Galaxies with peculiar morphologies have comparable angular momentum to disc galaxies of the same mass.

Abstract

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 $HST$ CANDELS imaging parametrically and non-parametrically. We combine the H$\alpha$ 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$_*$$\propto$M$_*^{0.53 \pm 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 Q$_{\rm g}$, H$\alpha$ star formation rate surface density $\Sigma_{\rm SFR}$) and its parameterised rest-frame UV/optical morphology (e.g. S\'ersic 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.