Dark Energy from Large-Scale Structure Lensing Information

TL;DR

This paper demonstrates that gravitational lensing distortions in large-scale structure surveys can be reconstructed to map dark matter distribution, providing valuable insights for dark energy and modified gravity studies.

Contribution

The authors develop an optimal quadratic lensing estimator for non-Gaussian large-scale structure sources, enabling effective dark matter mapping at high redshifts.

Findings

Lensing distortions can be reconstructed to map dark matter.

Reconstruction is effective on large scales (l <~ 100) at high redshifts.

Lensing information saturates at mildly non-linear scales due to information saturation.

Abstract

Wide area Large-Scale Structure (LSS) surveys are planning to map a substantial fraction of the visible universe to quantify dark energy through Baryon Acoustic Oscillations (BAO). At increasing redshift, for example that probed by proposed 21-cm intensity mapping surveys, gravitational lensing potentially limits the fidelity (Hui et al., 2007) because it distorts the apparent matter distribution. In this paper we show that these distortions can be reconstructed, and actually used to map the distribution of intervening dark matter. The lensing information for sources at z=1-3 allows accurate reconstruction of the gravitational potential on large scales, l <~ 100, which is well matched for Integrated Sachs-Wolfe (ISW) effect measurements of dark energy and its sound speed, and a strong constraint for modified gravity models of dark energy. We built an optimal quadratic lensing estimator for non-Gaussian sources, which is necessary for LSS. The phenomenon of "information saturation" (Rimes & Hamilton, 2005) saturates reconstruction at mildly non-linear scales, where the linear source power spectrum Delta^2 ~ 0.2-0.5. We find that steeper power spectra, saturate more quickly. We compute the effective number densities of independent lensing sources for LSS lensing, and find that they increase rapidly with redshifts. For LSS/21-cm sources at z ~ 2-4, the lensing reconstruction is limited by cosmic variance at l<~ 100.