Cosmic Shear Cosmology Beyond 2-Point Statistics: A Combined Peak Count and Correlation Function Analysis of DES-Y1

TL;DR

This paper presents a joint analysis of peak counts and two-point shear correlation functions from DES-Y1 data, providing a precise constraint on the structure growth parameter $S_8$ and demonstrating the potential of combining non-Gaussian and Gaussian statistics for cosmology.

Contribution

The study introduces a simulation-based method for joint peak-count and correlation function analysis, improving constraints on cosmological parameters from weak lensing data.

Findings

Measured $S_8$ with 4.8% precision from DES-Y1 data.

Demonstrated that combined analysis can reach 3% $S_8$ precision with calibration.

Showed robustness of constraints against simulation mass resolution and baryon feedback uncertainties.

Abstract

We constrain cosmological parameters from a joint cosmic shear analysis of peak-counts and the two-point shear correlation functions, as measured from the Dark Energy Survey (DES-Y1). We find the structure growth parameter $S_8\equiv \sigma_8\sqrt{\Omega_{\rm m}/0.3} = 0.766^{+0.033}_{-0.038}$, which at 4.8% precision, provides one of the tightest constraints on $S_8$ from the DES-Y1 weak lensing data. In our simulation-based method we determine the expected DES-Y1 peak-count signal for a range of cosmologies sampled in four $w$CDM parameters ($\Omega_{\rm m}$, $\sigma_8$, $h$, $w_0$). We also determine the joint covariance matrix with over 1000 realisations at our fiducial cosmology. With mock DES-Y1 data we calibrate the impact of photometric redshift and shear calibration uncertainty on the peak-count, marginalising over these uncertainties in our cosmological analysis. Using dedicated training samples we show that our measurements are unaffected by mass resolution limits in the simulation, and that our constraints are robust against uncertainty in the effect of baryon feedback. Accurate modelling for the impact of intrinsic alignments on the tomographic peak-count remains a challenge, currently limiting our exploitation of cross-correlated peak counts between high and low redshift bins. We demonstrate that once calibrated, a fully tomographic joint peak-count and correlation functions analysis has the potential to reach a 3% precision on $S_8$ for DES-Y1. Our methodology can be adopted to model any statistic that is sensitive to the non-Gaussian information encoded in the shear field. In order to accelerate the development of these beyond-two-point cosmic shear studies, our simulations are made available to the community upon request.