Non-linear Redshift-Space Power Spectra

Distances in cosmology are usually inferred from observed redshifts—an estimate that is dependent on the local peculiar motion—giving a distorted view of the three-dimensional structure and affecting basic observables such as the correlation function and power spectrum. We calculate the full nonlinear redshiftspace power spectrum for Gaussian fields, giving results for both the standard flat-sky approximation and the directly observable angular correlation function and angular power spectrum Clðz; z0Þ. Coupling between large and small-scale modes boosts the power on small scales when the perturbations are small. On larger scales power is slightly suppressed by the velocities perturbations on smaller scales. The analysis is general, but we comment specifically on the implications for future high-redshift observations and show that the nonlinear spectrum has significantly more complicated angular structure than in linear theory. We comment on the implications for using the angular structure to separate cosmological and astrophysical components of 21 cm observations.