A 2500 deg² CMB Lensing Map from Combined South Pole Telescope and Planck Data

We present a cosmic microwave background (CMB) lensing map produced from a linear combination of South Pole Telescope (SPT) and Planck temperature data. The 150 GHz temperature data from the 2500 deg² SPT-SZ survey is combined with the Planck 143 GHz data in harmonic space to obtain a temperature map that has a broader ℓ coverage and less noise than either individual map. Using a quadratic estimator technique on this combined temperature map, we produce a map of the gravitational lensing potential projected along the line of sight. We measure the auto-spectrum of the lensing potential C_L^φφ, and compare it to the theoretical prediction for a ΛCDM cosmology consistent with the Planck 2015 data set, finding a best-fit amplitude of 0.95_-0.06^+0.06(stat.)_0.01^+0.01(sys.). The null hypothesis of no lensing is rejected at a significance of 24σ. One important use of such a lensing potential map is in cross-correlations with other dark matter tracers. We demonstrate this cross-correlation in practice by calculating the cross-spectrum, C_L^φG, between the SPT+Planck lensing map and Wide-field Infrared Survey Explorer (WISE) galaxies. We fit C_L^φG to a power law of the form P_L = a(L/L₀)^-b with a, L ₀, and b fixed, and find η^φG = C_L^φG/P_L = 0.94_-0.04^+0.04, which is marginally lower, but in good agreement with η^φG = 1.00_-0.01^+0.02, the best-fit amplitude for the cross-correlation of Planck-2015 CMB lensing and WISE galaxies over ∼67% of the sky. The lensing potential map presented here will be used for cross-correlation studies with the Dark Energy Survey, whose footprint nearly completely covers the SPT 2500 deg² field.