Galaxy formation on the largest scales: the impact of astrophysics on the baryonic acoustic oscillation peak

We investigate the effects of galaxy formation on the baryonic acoustic oscillation (BAO) peak by applying semi-analytic modelling techniques to the Millennium-XXL, a 3 × 10¹¹ particle N-body simulation of similar volume to the future Euclid survey. Our approach explicitly incorporates the effects of tidal fields and stochasticity on halo formation, as well as the presence of velocity bias, spatially correlated merger histories, and the connection of all these with the observable and physical properties of galaxies. We measure significant deviations in the shape of the BAO peak from the expectations of a linear bias model built on top of the non-linear dark matter distribution. We find that the galaxy correlation function shows an excess close to the maximum of the BAO peak (r ∼ 110 h^-1 Mpc) and a deficit at r ∼ 90 h^-1 Mpc. Depending on the redshift, selection criteria and number density of the galaxy samples, these biased distortions can be up to 5 per cent in amplitude. They are, however, largely absorbed by marginalization over nuisance parameters in current analytical modelling of the BAO peak in configuration space, in particular into the parameter that controls the broadening due to non-linear evolution. As a result, the galaxy formation effects detected here are unlikely to bias the high-precision measurements planned by the upcoming generation of wide-field galaxy surveys.