# On the mass mismatch between simulations and weak-lensing measurements

## TL;DR

This study compares galaxy mass profiles from various cosmological simulations with weak lensing measurements, revealing a significant mismatch that persists across redshifts and is influenced by gas contributions, challenging current models of galaxy-halo connections.

## Contribution

It provides a detailed comparison of simulation-based and observational galaxy mass profiles, highlighting persistent discrepancies and the impact of gas contributions on weak lensing signals.

## Key findings

- Simulations produce higher mass profiles than observed, by about a factor of two.
- The mismatch remains consistent across different redshifts.
- Gas contributes 5-10% to the mass profiles in the one-halo regime.

## Abstract

The recently discovered discrepancy between galaxy mass measurements from weak lensing and predictions from abundance matching questions our understanding of cosmology, or of the galaxy-halo connection, or of both. We re-examined this tension by considering, as models, different cosmological simulations in the Illustris suite. We produced excess profiles $R\Delta\Sigma$ from subhalo snapshots at different redshifts in Illustris-1 and IllustrisTNG (TNG100 and TNG300) simulations, enabling a direct comparison with weak-lensing measurements. We separate the individual contributions of stars, dark matter and gas within $\approx1$ Mpc (comoving length), beyond which correlated two-halo terms dominate. The mismatch between measurements and predictions is more severe than in previous studies: $R\Delta\Sigma$ profiles from IllustrisTNG are $\approx2$ times higher than the measured ones. Contrary to abundance matching results, the mismatch is mostly unchanged with increasing redshifts. The contribution of gas to the $R\Delta\Sigma$ profiles is $5-10\%$ over the scales dominated by one-halo terms. Different procedures to link stellar and halo masses (abundance matching, cosmological simulations) are still significantly discrepant with weak lensing measurements, but their trends are different. Therefore, the change in cosmological parameters advocated through abundance-matching arguments may not resolve this tension. Also, current criteria to select isolated massive galaxies in simulations are susceptible to resolution issues and may not correspond to observational criteria. The (currently subdominant) contribution of gas is non-negligible, and even if the major discrepancy within stellar and halo masses is resolved, it will be an appreciable source of systematics in the LSST era, when uncertainties on the $R\Delta\Sigma$ profiles are expected to be $\approx10$ times smaller.