Effect of baryonic feedback on two- and three-point shear statistics: Prospects for detection and improved modelling

Abstract

Accurate knowledge of the effect of feedback from galaxy formation on the matter distribution is a key requirement for future weak lensing experiments. Recent studies using hydrodynamic simulations have shown that different baryonic feedback scenarios lead to significantly different two-point shear statistics. In this paper we extend earlier work to three-point shear statistics. We show that, relative to the predictions of dark matter only models, the amplitude of the signal can be reduced by as much as 30-40 per cent on scales of a few arcminutes. As is the case for two-point shear tomography, the interpretation of three-point shear statistics with dark matter only models is therefore plagued by a strong bias. However, we find that baryonic feedback may affect two- and three-point shear statistics differently and demonstrate that this can be used to assess the fidelity of various feedback models. In particular, upcoming surveys such as Euclid might be able to discriminate between different feedback models by measuring both second- and third-order shear statistics. Because it will likely remain impossible to predict baryonic feedback with high accuracy from first principles, we argue in favour of phenomenological models that can capture the relevant effects of baryonic feedback processes in addition to changes in cosmology. We construct such a model by modifying the standard (dark matter only) halo model to characterize the generic effects of energetic feedback using a small number of parameters. We use this model to perform a likelihood analysis in a simplified case in which two- and three-point shear statistics are measured over the range 0.5 < < 20 arcmin and in which the amplitude of fluctuations, σ8, the matter density parameter, Ωm, and the dark energy parameter,ω0, are the only unknown free parameters. We demonstrate that for weak lensing surveys such as Euclid, marginalizing over the feedback parameters describing the effects of baryonic processes, such as outflows driven by feedback from star formation and active galactic nuclei, may be able to mitigate the bias affecting Ωm, σ8 and ω0. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.