A hybrid multi resolution scheme to efficiently model the structure of reionization on the largest scales

Redshifted 21cm measurements of the structure of ionised regions that grow during reionization promise to provide a new probe of early galaxy and structure formation. One of the challenges of modelling reionization is to account both for the sub-halo scale physics of galaxy formation and the regions of ionization on scales that are many orders of magnitude larger. To bridge this gap we first calculate the statistical relationship between ionizing luminosity and Mpc-scale overdensity using detailed models of galaxy formation computed using relatively small volume - ($\sim$100Mpc/$h$)$^{3}$, high resolution dark matter simulations. We then use a Monte-Carlo technique to apply this relationship to reionization of the intergalactic medium within large volume dark matter simulations - ($>$1Gpc/$h$)$^{3}$. The resulting simulations can be used to address the contribution of very large scale clustering of galaxies to the structure of reionization, and show that volumes larger than 500Mpc/$h$ are required to probe the largest reionization features mid-way through reionization. As an example application of our technique, we demonstrate that the predicted 21cm power spectrum amplitude and gradient could be used to determine the importance of supernovae feedback for early galaxy formation.