Speaker
Description
Cosmological neutral hydrogen (HI) surveys provide a powerful tomographic probe of the post-reionization universe to test the standard model of cosmology. Efficiently simulating the HI signal is essential for optimizing the design and analysis strategies of upcoming surveys. We present a fast simulation method for the cosmological HI distribution employing the halo model framework. Dark matter halos are generated on the past light cone using the approximate yet efficient PINOCCHIO code and populated with HI via an empirical HI–halo mass relation. To meet the large-volume and high mass resolution requirements of 21 cm intensity mapping, we simulate a 1 $\mathrm{h}^{−3}\mathrm{Gpc}^3$ box with 6700$^3$ simulation particles, replicated to cover a light cone spanning declinations from –15° to –45° and frequencies from 700–800 MHz, matching the HIRAX (Hydrogen Intensity and Real-time Analysis eXperiment) survey footprint. The simulation resolves halo masses down to 4.3$\times$10$^9$ M$_⊙$, capturing over 97 % of the cosmic HI. After validating the simulation against the analytical dark matter and HI halo model, we demonstrate its use as an HI sky model for HIRAX. By incorporating galactic and extragalactic foregrounds as well as instrumental noise, we can forward model realistic telescope observations. The availability of a consistent halo catalogue further enables robust cross-correlation forecasts with other cosmological surveys. These forecasts will be particularly important for evaluating strategies for making the first statistically significant detection of the post-reionization signal with HIRAX which will be coming online this year.