Galaxy-Galaxy Lensing in EAGLE: comparison with data from 180 square degrees of the KiDS and GAMA surveys

TL;DR

This study compares galaxy-galaxy lensing predictions from the EAGLE simulation with observational data from KiDS and GAMA surveys, finding broad agreement and highlighting the importance of survey selection effects.

Contribution

It provides a detailed comparison of EAGLE simulation predictions with observational lensing data, emphasizing the role of survey selection functions in interpreting galaxy-dark matter connections.

Findings

Broad agreement between EAGLE and observations for central and satellite galaxies.

Underestimation of lensing signal at certain scales for high stellar mass bins.

Importance of accounting for survey selection effects in lensing analyses.

Abstract

We present predictions for the galaxy-galaxy lensing profile from the EAGLE hydrodynamical cosmological simulation at redshift z=0.18, in the spatial range 0.02 < R/(Mpc/h) < 2, and for five logarithmically equi-spaced stellar mass bins in the range 10.3 < $\log_{10}$(Mstar/ $M_{\odot}$) < 11.8. We compare these excess surface density profiles to the observed signal from background galaxies imaged by the Kilo Degree Survey around spectroscopically confirmed foreground galaxies from the GAMA survey. Exploiting the GAMA galaxy group catalogue, the profiles of central and satellite galaxies are computed separately for groups with at least five members to minimise contamination. EAGLE predictions are in broad agreement with the observed profiles for both central and satellite galaxies, although the signal is underestimated at R$\approx$0.5-2 Mpc/h for the highest stellar mass bins. When central and satellite galaxies are considered simultaneously, agreement is found only when the selection function of lens galaxies is taken into account in detail. Specifically, in the case of GAMA galaxies, it is crucial to account for the variation of the fraction of satellite galaxies in bins of stellar mass induced by the flux-limited nature of the survey. We report the inferred stellar-to-halo mass relation and we find good agreement with recent published results. We note how the precision of the galaxy-galaxy lensing profiles in the simulation holds the potential to constrain fine-grained aspects of the galaxy-dark matter connection.