Dark-ages reionization and galaxy formation simulation--VII. The sizes of high-redshift galaxies

TL;DR

This study uses a semi-analytic model to explore the sizes of high-redshift galaxies, confirming the importance of supernova feedback in shaping galaxy size evolution during reionization.

Contribution

The paper presents a semi-analytic model that accurately reproduces galaxy size-luminosity relations and their evolution, emphasizing the role of supernova feedback.

Findings

Galaxy sizes scale with luminosity as R_e ∝ L^0.25 at z~5-9.

Predicted size-luminosity relations match observed luminous galaxies at z~7 and z~11.

Supernova feedback is crucial; models without it produce smaller, inconsistent galaxy sizes.

Abstract

We investigate high-redshift galaxy sizes using a semi-analytic model constructed for the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulation project. Our fiducial model, including strong feedback from supernovae and photoionization background, accurately reproduces the evolution of the stellar mass function and UV luminosity function. Using this model, we study the size--luminosity relation of galaxies and find that the effective radius scales with UV luminosity as $R_\mathrm{e}\propto L^{0.25}$ at $z{\sim}5$--$9$. We show that recently discovered very luminous galaxies at $z{\sim}7$ (Bowler et al. 2016) and $z{\sim}11$ (Oesch et al. 2016) lie on our predicted size--luminosity relations. We find that a significant fraction of galaxies at $z>8$ will not be resolved by JWST, but GMT will have the ability to resolve all galaxies in haloes above the atomic cooling limit. We show that our fiducial model successfully reproduces the redshift evolution of average galaxy sizes at $z>5$. We also explore galaxy sizes in models without supernova feedback. The no-supernova feedback models produce galaxy sizes that are smaller than observations. We therefore confirm that supernova feedback plays an important role in determining the size--luminosity relation of galaxies and its redshift evolution during reionization.