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

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 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 * ∝ M 0.53 ± 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 Q g , Hα star formation rate surface density Σ SFR ) and its parameterised restframe UV / optical morphology (e.g. Sérsic index, bulge to total ratio, Clumpiness, Asymmetry and Concentration). We establish that the position in the j * -M * plane is 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.

The MUSEHubbleUltra Deep Field Survey

“…Given the difficulties in measuring j(<r) in the outskirts of galaxies, a method that is commonly used in the literature (e.g., Burkert et al 2016;Swinbank et al 2017;Harrison et al 2017;Gillman et al 2020) for estimating j tot is the following formulae (Romanowsky & Fall 2012, hereafter RF12):…”

“…These surveys (and others, e.g. Alcorn et al 2018;Gillman et al 2020) are often limited to relatively massive SFGs with a typical limit of M > 10 9.5 M .…”

The KMOS galaxy evolution survey (KGES): the angular momentum of star-forming galaxies over the last ≈10 Gyr

“…The derivation of stellar masses for the KGES sample is described in detail in Gillman et al (2020). In summary, a stellar mass estimate for each KGES galaxy was obtained via the application, in Dudzevičiūtė et al (2020), of the Multi-wavelength Analysis of Galaxy Physical Properties (MAGPHYS; da Cunha, Charlot & Elbaz 2008) SED fitting routine to model its SED.…”

“…The stellar light structural parameters of the KGES galaxies, including their axial-ratio derived inclinations, their Sérsic indices, and the stellar half-light radii were measured by Gillman et al (2020) via the application of the GALFIT (Peng et al 2010) Sérsic modelling code to the highest resolution, deepest, and reddest-wavelength broad-band image available for each galaxy. The GALFIT routine accounts for the size of the image PSF in each case, providing an intrinsic best-fitting model of the 2D stellar light distribution.…”

“…that of an exponential disc. Gillman et al (2020) measured n S for each KGES galaxy, and a similar measurement is available for each SAMI galaxy via modelling of its r-band image (Kelvin et al 2012). However, since a measure of n S is only available for a subset of KROSS galaxies (see Harrison et al 2017 for further details), we avoid an extended comparison of n S for galaxies in our kinematics subsamples at each redshift.…”