The Atacama Cosmology Telescope: A CMB lensing mass map over 2100 square degrees of sky and its cross-correlation with BOSS-CMASS galaxies

We construct cosmic microwave background lensing mass maps using data from
the 2014 and 2015 seasons of observations with the Atacama Cosmology Telescope
(ACT). These maps cover 2100 square degrees of sky and overlap with a wide variety
of optical surveys. The maps are signal dominated on large scales and have fidelity
such that their correlation with the cosmic infrared background is clearly visible by
eye. We also create lensing maps with thermal Sunyaev-Zel’dovich contamination
removed using a novel cleaning procedure that only slightly degrades the lensing
signal-to-noise ratio. The cross-spectrum between the cleaned lensing map and the
BOSS CMASS galaxy sample is detected at 10-σ significance, with an amplitude of
A = 1.02±0.10 relative to the Planck best-fit LCDM cosmological model with fiducial
linear galaxy bias. Our measurement lays the foundation for lensing cross-correlation
science with current ACT data and beyond.