Impact of astrophysics on cosmology forecasts for 21 cm surveys

We use the results of previous work building a halo model formalism for the distribution of neutral hydrogen, along with experimental parameters of future radio facilities, to place forecasts on astrophysical and cosmological parameters from next-generation surveys. We consider 21 cm intensity mapping surveys conducted using the BINGO, CHIME, FAST, TianLai, MeerKAT, and SKA experimental configurations. We work with the five-parameter cosmological data set of {Ωm, σ8, h, ns, Ωb} assuming a flat ΛCDM model, and the astrophysical parameters {vc,0, β} which represent the cut-off and slope of the H I–halo mass (H IHM) relation. We explore (i) quantifying the effects of the astrophysics on the recovery of the cosmological parameters, (ii) the dependence of the cosmological forecasts on the details of the astrophysical parametrization, and (iii) the improvement of the constraints on probing smaller scales in the H I power spectrum. For an SKA I MID intensity mapping survey alone, probing scales up to ℓmax = 1000, we find a factor of 1.1–1.3 broadening in the constraints on Ωb and Ωm, and of 2.4–2.6 on h, ns and σ8, if we marginalize over astrophysical parameters without any priors. However, even the prior information coming from the present knowledge of the astrophysics largely alleviates this broadening. These findings do not change significantly on considering an extended H IHM relation, illustrating the robustness of the results to the choice of the astrophysical parametrization. Probing scales up to ℓmax = 2000 improves the constraints by factors of 1.5–1.8. The forecasts improve on increasing the number of tomographic redshift bins, saturating, in many cases, with 4–5 redshift bins. We also forecast constraints for intensity mapping with other experiments, and draw similar conclusions.