Description
The redshift range 3 < z < 6 is an important transitionary period in our Universe’s history, wherein reionization concludes, leaving behind a completely ionized intergalactic medium. Neutral hydrogen (HI) remains only in small islands located towards the centre of halos, where the medium is sufficiently dense to self-shield from ionizing photons.
Consequently, during this time, the HI brightness temperature field goes from being a measure of the astrophysics of reionization to a tracer of the cosmic web. Therefore, the post-reionization HI power spectrum presents itself as not only a rich source of information on cosmic structure at high redshift, but also an additional constraint on reionization end.
To examine the detectability of this transition, we have been working on a semi-analytic simulation of the post-reionization HI signal. We build off of the reionization code 21cmFAST, utilising its capacity for 2nd-order Lagrangian perturbation theory to evolve the overdensity field to late times. From here, we apply a post-processing pipeline to obtain the post-reionization HI brightness temperature field, involving a watershed-based algorithm to identify halos, a HI-halo mass relation to determine the total HI mass associated with each halo, and a radial density profile to distribute the HI about each halo.
We will present our simulation pipeline, alongside predictions of the signal-to-noise for a range of planned SKA-LOW surveys. We will also present preliminary findings on the detectability of this transition period, and the potential for this data to contribute to constraints on key cosmological parameters and the astrophysics of reionization.
