An Estimator for the lensing potential from galaxy number counts

TL;DR

This paper introduces a new estimator for the lensing potential using galaxy number counts, which significantly improves signal-to-noise ratio over intensity mapping, especially at high redshifts, enabling effective tomographic lensing measurements.

Contribution

The paper presents a novel estimator for the lensing potential from galaxy number counts that includes linear and quadratic terms, enhancing measurement accuracy.

Findings

Estimator has higher signal-to-noise ratio than intensity mapping.

Signal-to-noise ratio can reach around 30 at redshifts above 1.5.

Number counts in photometric surveys are effective for tomographic lensing spectra.

Abstract

We derive an estimator for the lensing potential from galaxy number counts which contains a linear and a quadratic term. We show that this estimator has a much larger signal-to-noise ratio than the corresponding estimator from intensity mapping. We show that this is due to the additional lensing term in the number count angular power spectrum which is present already at linear order. We estimate the signal-to-noise ratio for future photometric surveys. We find that particularly at high redshifts, $z\gtrsim 1.5$, the signal to noise ratio can become of order 30. We therefore claim that number counts in photometric surveys are an excellent means to measure tomographic lensing spectra.