Astraeus IV: quantifying the star formation histories of galaxies in the Epoch of Reionization

We use the \textsc{astraeus} framework, that couples an N-body simulation with a semi-analytic model for galaxy formation and semi-numerical reionization, to quantify star histories (SFHs) of galaxies in first billion years. Exploring four models radiative feedback, we fit SFH each at $z>5$ as $\mathrm{log}(\mathrm{SFR}(z))=-\alpha(1 + z)+\beta$; is deemed stochastic if it deviates from this by more than $\Delta_\mathrm{SFR}=0.6\,$dex. Our key findings are: (i) The fraction stellar mass formed time spent phase decrease increasing redshift $z$. While masses $M_\star\sim10^7M_\odot$ $z\sim5~(10)$ form $\sim70\%~(20\%)$ their phase, reduces $<10\%$ all redshifts $M_\star > 10^{10}M_\odot$; (ii) fractional assembled lifetime do not significantly change feedback used; (iii) redshifts, $\alpha$ increases (decreases strongest model) $M_\star\lesssim 10^{8.5}M_\odot$ converges $\sim0.18$ massive galaxies; $\beta$ always mass. proposed fits can reliably recover mass-to-light ratios $M_\star\sim10^{8-10.5}M_\odot$ $M_{UV}\sim-17~{\rm to}~-23$ $z\sim 5-9$. This physical therefore be used derive SFHs observed number forthcoming instruments.