Baryon oscillations

Abstract

The coupling of photons and baryons by Thomson scattering in the early universe imprints features in both the cosmic microwave background (CMB) and matter power spectra. The former have been used to constrain a host of cosmological parameters, the latter have the potential to strongly constrain the expansion history of the universe and dark energy. Key to this program is the means to localize the primordial features in observations of galaxy spectra which necessarily involve galaxy bias, non-linear evolution and redshift space distortions. We present calculations, based on mock catalogues produced from particle-mesh simulations, which show the range of behaviors we might expect of galaxies in the real universe. We find that non-linearity, galaxy bias and redshift space distortions all introduce important modifications to the basic picture. Both the galaxy bias and the (isotropic) redshift space distortions lead to relatively smooth modulations in power on the scales of interest to baryon oscillations. The halo and galaxy power spectra exhibit low order structure beyond the acoustic oscillations over the range of scales of relevance. Fitting a cubic polynomial to the ratio of galaxy to dark matter power reduces any remaining structure in the range 0.03 ⩽ k ⩽ 0.3 h Mpc −1 below the 2% level, which is close to the error in our calculations.