Probing gravity with the DES-CMASS sample and BOSS spectroscopy

The DES-CMASS sample (DMASS) is designed to optimally combine the weak lensing measurements from the Dark Energy Survey (DES) and redshift-space distortions (RSD) probed by the CMASS galaxy sample from the Baryonic Oscillation Spectroscopic Survey. In this paper, we demonstrate the feasibility of adopting DMASS as the equivalent of CMASS for a joint analysis of DES and BOSS in the framework of modified gravity. We utilize the angular clustering of the DMASS galaxies, cosmic shear of the DES METACALIBRATION sources, and cross-correlation of the two as data vectors. By jointly fitting the combination of the data with the RSD measurements from the CMASS sample and Planck data, we obtain the constraints on modified gravity parameters mu(0) = -0.37(-0.45)(+0.47) and Sigma(0) = 0.078(-0.082)(+0.078). Our constraints of modified gravity with DMASS are tighter than those with the DES Year 1 REDMAGIC sample with the same external data sets by 29 per cent for mu(0) and 21 per cent for Sigma(0), and comparable to the published results of the DES Year 1 modified gravity analysis despite this work using fewer external data sets. This improvement is mainly because the galaxy bias parameter is shared and more tightly constrained by both CMASS and DMASS, effectively breaking the degeneracy between the galaxy bias and other cosmological parameters. Such an approach to optimally combine photometric and spectroscopic surveys using a photometric sample equivalent to a spectroscopic sample can be applied to combining future surveys having a limited overlap such as DESI and LSST.

Automated summary

This paper demonstrates the feasibility of using the DES-CMASS sample (DMASS) as the equivalent of CMASS for a joint analysis of DES and BOSS in the framework of modified gravity. By combining the data vectors of DMASS galaxies' angular clustering, DES METACALIBRATION sources' cosmic shear, and cross-correlation of the two, along with RSD measurements from the CMASS sample and Planck data, we obtain constraints on modified gravity parameters mu(0) and Sigma(0). The constraints obtained with DMASS are tighter than those with other samples using the same external data sets, indicating the effectiveness of this approach in breaking the degeneracy between galaxy bias and other cosmological parameters.