The redshift-space galaxy two-point correlation function and baryon acoustic oscillations

Future galaxy surveys will measure baryon acoustic oscillations (BAOs) with high significance and a complete understanding of the anisotropies of BAOs in redshift space will be important to exploit the cosmological information in BAOs. Here we describe the anisotropies that arise in the redshift-space galaxy two-point correlation function (2PCF) and elucidate the origin of features that arise in the dependence of BAOs on the angle between the orientation of the galaxy pair and the line of sight. We do so with a derivation of the configuration-space 2PCF using the streaming model. We find that, contrary to common belief, the locations of BAO peaks in the redshift-space 2PCF are anisotropic even in linear theory. Anisotropies in BAO depend strongly on the method of extracting the peak, showing a maximum of 3 per cent angular variation. We also find that extracting the BAO peak of the radius-square-weighted 2PCF, r²ξ (r, μ), where μ is the cosine between the line of sight and separation, reduces the anisotropy significantly to sub-per-cent level angular variations. When subtracting the tilt due to the broad-band behaviour of the 2PCF, the BAO bump is enhanced along the line of sight because of local infall velocities towards the BAO bump. Moving beyond the BAOs, precise measurement of the angular dependence of the redshift-space 2PCF on large scales, where linear theory models the anisotropies accurately, will allow new geometrical tests of dark energy.