The impact of baryons on the sensitivity of dark energy measurements

Baryonic effects on large-scale structure, if not accounted for, can significantly bias dark energy constraints. As the detailed physics of the baryons is not yet well understood, correcting for baryon effects introduces additional parameters which must be marginalized over, increasing the uncertainties on the inferred cosmological parameters. Forthcoming weak lensing surveys are aiming for percent-level precision on the dark energy equation of state, so the problem must be thoroughly examined. We use a halo model with analytic modifications which capture the impact of adiabatic contraction of baryons and feedback on the matter power spectrum, and generalize the Navarro-Frenk-White profile to account for a possible inner core. A Fisher analysis predicts degradations of 40 per cent in the w₀ - w_a Figure of Merit for a Euclidlike survey, and up to 80 per cent for other cosmological parameters. We forecast potential inner core constraints of a few kpc, while for a fixed inner core, adiabatic concentration and feedback parameters are constrained to a few per cent. We explore the scales where baryons and dark energy contribute most to the Fisher information, finding that probing to increasingly non-linear scales does little to reduce degradation. Including external baryon information improves our forecasts, but limiting degradation to 1 per cent requires strong priors. Adding Planck cosmic microwave background priors improves the Figure of Merit by a factor of 2.7 and almost completely recovers the individual marginalized errors on w₀ and w_a. We also quantify the calibration of baryon modelling required to reduce biases of dark energy forecasts to acceptable levels for forthcoming lensing surveys.