Accounting for baryonic effects in cosmic shear tomography: Determining a minimal set of nuisance parameters using PCA

TL;DR

This paper introduces PCA marginalization as a method to incorporate and reduce the impact of baryonic uncertainties in cosmic shear analyses, enabling unbiased and precise cosmological constraints.

Contribution

The paper presents a novel PCA marginalization framework to efficiently account for baryonic effects as nuisance parameters in cosmic shear tomography.

Findings

PCA marginalization effectively removes biases caused by baryonic physics.

Using 3-4 nuisance parameters suffices to capture baryonic uncertainties.

The method yields robust dark energy constraints despite systematic uncertainties.

Abstract

Systematic uncertainties that have been subdominant in past large-scale structure (LSS) surveys are likely to exceed statistical uncertainties of current and future LSS data sets, potentially limiting the extraction of cosmological information. Here we present a general framework (PCA marginalization) to consistently incorporate systematic effects into a likelihood analysis. This technique naturally accounts for degeneracies between nuisance parameters and can substantially reduce the dimension of the parameter space that needs to be sampled. As a practical application, we apply PCA marginalization to account for baryonic physics as an uncertainty in cosmic shear tomography. Specifically, we use CosmoLike to run simulated likelihood analyses on three independent sets of numerical simulations, each covering a wide range of baryonic scenarios differing in cooling, star formation, and feedback mechanisms. We simulate a Stage III (Dark Energy Survey) and Stage IV (Large Synoptic Survey Telescope/Euclid) survey and find a substantial bias in cosmological constraints if baryonic physics is not accounted for. We then show that PCA marginalization (employing at most 3 to 4 nuisance parameters) removes this bias. Our study demonstrates that it is possible to obtain robust, precise constraints on the dark energy equation of state even in the presence of large levels of systematic uncertainty in astrophysical processes. We conclude that the PCA marginalization technique is a powerful, general tool for addressing many of the challenges facing the precision cosmology program.