Lensing reconstruction from line intensity maps: the impact of gravitational nonlinearity

Understand

We investigate the detection prospects for gravitational lensing of three-dimensional maps from upcoming line intensity surveys, focusing in particular on the impact of gravitational nonlinearities on standard quadratic lensing estimators.

• Using perturbation theory, we show that these nonlinearities can provide a significant contaminant to lensing reconstruction, even for observations at reionization-era redshifts.
• However, we show how this contamination can be mitigated with the use of a "bias-hardened" estimator.
• Along the way, we present an estimator for reconstructing long-wavelength density modes, in the spirit of the "tidal reconstruction" technique that has been proposed elsewhere, and discuss the dominant biases on this estimator.