The galaxy–halo size relation of low-mass galaxies in FIRE

Galaxy sizes correlate closely with the of their parent dark matter haloes, suggesting a link between halo formation and galaxy growth. However, precise nature this relation its scatter remains to be understood fully, especially for low-mass galaxies. We analyse galaxy-halo size ($M_\star \sim 10^{7-9} {\rm M_\odot}$) central galaxies over past 12.5 billion years help cosmological volume simulations (FIREbox) from Feedback in Realistic Environments (FIRE) project. find nearly linear relationship half-stellar mass $R_{1/2}$ virial radius $R_{\rm vir}$. This evolves only weakly since redshift $z = 5$: $R_{1/2} kpc} (0.053\pm0.002)(R_{\rm vir}/35 kpc})^{0.934\pm0.054}$, constant $\langle \sigma \rangle 0.084 [{\rm dex}]$. Whilst ratio is similar what expected models where disc are set by angular momentum, our sample not momentum supported, stellar rotational circular velocity ratios $v_{\rm rot} / v_{\rm circ} 0.15$. Introducing as another parameter GHSR does decrease scatter. Furthermore, any properties we investigate -- including spin concentration that baryonic processes feedback physics instead critical setting relation. Given relatively small weak dependence on these galaxies, propose using an independent method masses infer masses.