Joint analysis of Dark Energy Survey Year 3 data and CMB lensing from SPT and <i>Planck</i> . I. Construction of CMB lensing maps and modeling choices

Joint analyses of cross-correlations between measurements galaxy positions, lensing, and lensing the cosmic microwave background (CMB) offer powerful constraints on large-scale structure Universe. In a forthcoming analysis, we will present cosmological from analysis such measured using Year 3 data Dark Energy Survey (DES), CMB South Pole Telescope (SPT) Planck. Here two key ingredients this analysis: (1) an improved map in SPT-SZ survey footprint, (2) methodology that be used to extract information cross-correlation measurements. Relative previous maps made same observations, have implemented techniques remove contamination thermal Sunyaev Zel'dovich effect, enabling extraction smaller angular scales than with DES 1 data. We describe our model for these data, validate modeling choices demonstrate robustness analysis. then forecast expected survey-CMB auto cross-correlations. find galaxy-CMB shear-CMB correlations their own provide constraint $S_8=\sigma_8 \sqrt{\Omega_{\rm m}/0.3}$ at few percent level, providing consistency check DES-only constraints. explore scenarios where external priors shear calibration are removed, finding joint can amplitude 5 10% level.