Weak Lensing by Photometric Density Ridges

TL;DR

This paper reports the detection of weak gravitational lensing caused by cosmic web filaments identified as density ridges in galaxy surveys, using improved algorithms on DES data, and explores its dependence on cosmological parameters.

Contribution

It introduces enhanced algorithms for locating density ridges in galaxy surveys and demonstrates their use in detecting lensing effects related to cosmic filaments in DES data.

Findings

Detected lensing signal at high significance in DES Year 3 data.

Lensing signal primarily depends on the parameter S8.

Methodological improvements needed for precision cosmology.

Abstract

Ridges in galaxy density fields measured by photometric surveys are 2D projections of filaments in the cosmic web, and so should lens light from background galaxies. We report on a detection of this effect in Dark Energy Survey Year 3 data at high significance, though not independently of galaxy-galaxy lensing. We describe improvements to the existing subspace-constrained mean shift algorithm to locate these ridges efficiently at scale, and examine the dependence of the signal in simulations on cosmological and algorithmic parameters. We find that it depends primarily on $S_8=\sigma_8 \left( \Omega_m / 0.3 \right)^{1/2}$, and discuss improvements to our methodology that would be needed to allow precision parameter estimation.