Lensing is Low: Cosmology, Galaxy Formation, or New Physics?

TL;DR

This study measures galaxy-galaxy lensing in the BOSS CMASS sample, finding a lower signal than standard models predict, and discusses potential explanations including cosmological parameters and galaxy-halo physics.

Contribution

It provides high-precision lensing measurements and compares them with mock catalogs, highlighting discrepancies and exploring various physical effects that could explain them.

Findings

Lensing signal is 20-40% lower than model predictions.

Lowering S8 reconciles lensing with clustering data.

Multiple physical effects may influence the lensing signal.

Abstract

We present high signal-to-noise galaxy-galaxy lensing measurements of the BOSS CMASS sample using 250 square degrees of weak lensing data from CFHTLenS and CS82. We compare this signal with predictions from mock catalogs trained to match observables including the stellar mass function and the projected and two dimensional clustering of CMASS. We show that the clustering of CMASS, together with standard models of the galaxy-halo connection, robustly predicts a lensing signal that is 20-40% larger than observed. Detailed tests show that our results are robust to a variety of systematic effects. Lowering the value of $S_{\rm 8}=\sigma_{\rm 8} \sqrt{\Omega_{\rm m}/0.3}$ compared to Planck2015 reconciles the lensing with clustering. However, given the scale of our measurement ($r<10$ $h^{-1}$ Mpc), other effects may also be at play and need to be taken into consideration. We explore the impact of baryon physics, assembly bias, massive neutrinos, and modifications to general relativity on $\Delta\Sigma$ and show that several of these effects may be non-negligible given the precision of our measurement. Disentangling cosmological effects from the details of the galaxy-halo connection, the effects of baryons, and massive neutrinos, is the next challenge facing joint lensing and clustering analyses. This is especially true in the context of large galaxy samples from Baryon Acoustic Oscillation surveys with precise measurements but complex selection functions.