The Impact of Baryons on Cosmological Inference from Weak Lensing Statistics

TL;DR

This study models baryonic effects in weak lensing to understand their impact on cosmological parameter inference, revealing that baryons significantly degrade constraints unless external information is used.

Contribution

It introduces a comprehensive baryonic correction model integrated into N-body simulations across multiple cosmologies, analyzing its effect on weak lensing statistics and parameter constraints.

Findings

Baryonic effects degrade cosmological constraints by a factor of 2-4.

Ejected gas distance (AGN feedback) most impacts parameter degeneracy.

External constraints on baryonic parameters can mitigate degradation.

Abstract

As weak lensing surveys are becoming deeper and cover larger areas, information will be available on small angular scales down to the arcmin level. To extract this extra information, accurate modelling of baryonic effects is necessary. In this work, we adopt a baryonic correction model, which includes gas both bound inside and ejected from dark matter (DM) haloes, a central galaxy, and changes in the DM profile induced by baryons. We use this model to incorporate baryons into a large suite of DM-only $N$-body simulations, covering a grid of 75 cosmologies in the $\Omega_\mathrm{m}-\sigma_8$ parameter space. We investigate how baryons affect Gaussian and non-Gaussian weak lensing statistics and the cosmological parameter inferences from these statistics. Our results show that marginalizing over baryonic parameters degrades the constraints in $\Omega_\mathrm{m}-\sigma_8$ space by a factor of $2-4$ compared to those with baryonic parameters fixed. We investigate the contribution of each baryonic component to this degradation, and find that the distance to which gas is ejected (from AGN feedback) has the largest impact due to its degeneracy with cosmological parameters. External constraints on this parameter, either from other datasets or from a better theoretical understanding of AGN feedback, can significantly mitigate the impact of baryons in an HSC-like survey.