A new estimator for gravitational lensing using galaxy and intensity mapping surveys

We propose a new tomographic estimator for the gravitational lensing potential, based on a combination of intensity mapping (IM) and galaxy counts. The estimator can be written schematically as IM×galaxy − galaxy×IM; this combination allows to greatly reduce the contamination by density-density correlations, thus isolating the lensing signal. We show that the new estimator improves the signal-to-noise ratio for the detection of lensing especially on linear scales and intermediate redshifts. This makes it particularly valuable for future studies of dark energy and modified gravity. For cosmic variance dominated surveys the signal-to-noise ratio is improved by a factor of around 20-30 on linear scales (ℓmax=200), with a lower improvement of around 5-10 if one includes smaller scales (ℓmax=1000). Shot noise and interferometer noise reduce the relative improvement to about 1.5-2 for the specific examples of DES and Euclid cross-correlated with HIRAX. Our estimator is additionally less susceptible to systematic effects as it only involves cross-correlations.