Galaxy sizes in the early Universe

We present preliminary results of a study of galaxy sizes at redshift $z\gtrsim 5$ using the high-resolution, zoom-in $\text{textsc}FirstLight$ simulations. We obtain a redshift-independent, chevron-shaped stellar mass–size relation with a peak at $M^{\star }\approx {10}^{8.5}{\mathrm{M}}_{\odot }$. This relation is shaped by the individual evolution of galaxies, which undergo a phase of contraction at this mass scale triggered by a strong central starburst.