A Hybrid Approach Toward Simulating Reionization: Coupling Ray Tracing with Excursion Sets

Abstract

Abstract This paper introduces a new method of generating 21 cm maps that is based on ideas from ray tracing and excursion sets. In this method, photons generated in each grid cell are computed using the excursion set ideas while their propagation is accounted for by ray tracing. The method requires the overdensity field over a grid as a starting point. Then the usual reionization parameters, minimum mass of collapsed halos (M min), number of ionizing photons deposited in the intergalactic medium per collapsed baryon (n ion), and ratio of ionization rate to recombination rate (represented through n rec) are used. Thus, this is a hybrid method that utilizes the results of theoretically motivated excursion sets and combines them with the computationally intensive procedure of ray tracing. As the method integrates simple principles of both the approaches, it is expected to yield precise and fast estimates of the power spectrum on the scales of interest (0.1 Mpc−1 ≲ k ≲ 1.0 Mpc−1).