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 Surv e y (DES) and redshift-space distortions (RSD) probed by the CMASS galaxy sample from the Baryonic Oscillation Spectroscopic Surv e y. In this paper, we demonstrate the feasibility of adopting DMASS as the equi v alent 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 μ0 = −0 . 37 + 0 . 47 −0 . 45 and 0 = 0 . 078 + 0 . 078 −0 . 082 . 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 μ0 and 21 per cent for 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, ef fecti vely breaking the de generac y between the galaxy bias and other cosmological parameters. Such an approach to optimally combine photometric and spectroscopic surv e ys using a photometric sample equi v alent to a spectroscopic sample can be applied to combining future surv e ys having a limited o v erlap such as DESI and LSST.