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 5-parameter cosmological dataset
of {$\Omega_m, \sigma_8, h, n_s, \Omega_b$} assuming a flat $\Lambda$CDM model,
and the astrophysical parameters {$v_{c,0}, \beta$} which represent the cutoff
and slope of the HI- halo mass 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 HI power spectrum. For an SKA I MID intensity mapping
survey alone, probing scales up to $\ell_{\rm max} = 1000$, we find a factor of
$1.1 - 1.3$ broadening in the constraints on $\Omega_b$ and $\Omega_m$, and of
$2.4 - 2.6$ on $h$, $n_s$ and $\sigma_8$, 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 HIHM
relation, illustrating the robustness of the results to the choice of the
astrophysical parametrization. Probing scales up to $\ell_{\rm max} = 2000$
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.
