Combining Weak Lensing Tomography with Halo Clustering to Probe Dark Energy

TL;DR

This paper investigates whether combining weak lensing tomography with halo clustering in a single survey enhances dark energy constraints, finding that their correlation does not weaken and can slightly improve results, simplifying analysis.

Contribution

The study demonstrates that in a DES-like survey, the correlation between weak lensing and halo clustering does not reduce the effectiveness of combined dark energy constraints, allowing for simplified, nearly independent analyses.

Findings

Correlations between weak lensing and halo clustering are high but do not degrade constraints.

Combining the two methods yields constraints that are as good as or slightly better than separate analyses.

Treating weak lensing and halo clustering as independent is justified for DES-like surveys.

Abstract

Two methods of constraining the properties of dark energy are weak lensing tomography and cluster counting. Uncertainties in mass calibration of clusters can be reduced by using the properties of halo clustering (the clustering of clusters). However, within a single survey, weak lensing and halo clustering probe the same density fluctuations. We explore the question of whether this information can be used twice -- once in weak lensing and then again in halo clustering to calibrate cluster masses -- or whether the combined dark energy constraints are weaker than the sum of the individual constraints. For a survey like the Dark Energy Survey (DES), we find that the cosmic shearing of source galaxies at high redshifts is indeed highly correlated with halo clustering at lower redshifts. Surprisingly, this correlation does not degrade cosmological constraints for a DES-like survey, and in fact, constraints are marginally improved since the correlations themselves act as additional observables. This considerably simplifies the analysis for a DES-like survey: when weak lensing and halo clustering are treated as independent experiments, the combined dark energy constraints (cluster counts included) are accurate if not slightly conservative. Our findings mirror those of Takada and Bridle, who investigated correlations between the cosmic shear and cluster counts.