Recovering the coupled treatment of redshift-space distortions and the light-cone effect after diffuse foreground removal

ABSTRACT The 21 cm brightness temperature during the Epoch of Reionization is widely modelled using seminumeric simulations, used for their computational speed and flexibility in testing astrophysical and cosmological parameters. However, it is common practice to simulate coeval brightness temperature boxes, and then apply post-processing algorithms that treat the light-cone effect and redshift-space distortions separately, assuming they can be added in sequence. We instead model them together, allowing for partial coeval cell contributions, and ensuring that velocity-induced frequency shifts are computed at the correct cosmic time for every position along the line of sight. We show that considering these effects simultaneously creates a difference in the shape of the power spectrum over all Fourier scales, and remains recoverable after semiblind foreground removal. We show that our light-cones consist of an average of 8 per cent and maximum of 120 per cent of a coeval cell length. These contributions to a 21 cm brightness temperature light-cone voxel are shifted from within a $\pm 0.5$ MHz range of the emitted frequency. The boost in the power spectrum seen over small scales ($k>1.5$ Mpc) of our robust 21 cm light-cone method compared to basic methods is recoverable after the addition and removal of diffuse radio foregrounds. The largest differences during the Epoch of Reionization lie in the k-space, where the noise sensitivity for a 1000-h SKAO-low observation is greater than the signal. However, in the cosmic dawn, we have shown that the major differences lie outside of this noise-dominated region.