# Dark-ages Reionization and Galaxy Formation Simulation -- XVII. Sizes, angular momenta and morphologies of high redshift galaxies

## TL;DR

This study uses an updated semi-analytic model to explore high-redshift galaxy sizes, angular momenta, and morphologies, successfully matching observations from redshifts 0 to 10 and revealing how these properties evolve over cosmic time.

## Contribution

The paper introduces an improved model that accurately predicts galaxy sizes, angular momentum ratios, and morphologies across a wide redshift range, highlighting the evolution of these properties.

## Key findings

- Galaxy sizes scale with UV luminosity and stellar mass.
- Median galaxy size decreases with redshift approximately as (1+z)^{-2}.
- High-redshift galaxies are predominantly bulge-dominated.

## Abstract

We study the sizes, angular momenta and morphologies of high-redshift galaxies using an update of the Meraxes semi-analytic galaxy evolution model. Our model successfully reproduces a range of observations from redshifts $z=0$-$10$. We find that the effective radius of a galaxy disc scales with UV luminosity as $R_e\propto L_{\textrm{UV}}^{0.33}$ at $z=5$-$10$, and with stellar mass as $R_e\propto M_\ast^{0.24}$ at $z=5$ but with a slope that increases at higher redshifts. Our model predicts that the median galaxy size scales with redshift as $R_e \propto (1+z)^{-m}$, where $m=1.98\pm0.07$ for galaxies with $(0.3$-$1)L^\ast_{z=3}$ and $m=2.15\pm0.05$ for galaxies with $(0.12$-$0.3)L^\ast_{z=3}$. We find that the ratio between stellar and halo specific angular momentum is typically less than one and decreases with halo and stellar mass. This relation shows no redshift dependence, while the relation between specific angular momentum and stellar mass decreases by $\sim0.5$ dex from $z=7$ to $z=2$. Our model reproduces the distribution of local galaxy morphologies, with bulges formed predominantly through galaxy mergers for low-mass galaxies, disc-instabilities for galaxies with $M_\ast\simeq10^{10}$-$10^{11.5}M_\odot$, and major mergers for the most massive galaxies. At high redshifts, we find galaxy morphologies that are predominantly bulge-dominated.