A comparison of the excess mass around CFHTLenS galaxy-pairs to predictions from a semi-analytic model using galaxy-galaxy-galaxy lensing

TL;DR

This study maps the distribution of matter around galaxy pairs using galaxy-galaxy-galaxy lensing in CFHTLenS and compares it to semi-analytic model predictions, finding overall good agreement but some localized discrepancies.

Contribution

First comparison of excess mass maps from galaxy-galaxy-galaxy lensing with semi-analytic model predictions within the Millennium Simulation.

Findings

Detected excess mass with 3-6 sigma significance.

Observed general agreement with model predictions.

Identified localized discrepancies possibly due to systematic effects or physical processes.

Abstract

The matter environment of galaxies is connected to the physics of galaxy formation and evolution. Utilising galaxy-galaxy-galaxy lensing as a direct probe, we map out the distribution of correlated surface mass-density around galaxy pairs for different lens separations in the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). We compare, for the first time, these so-called excess mass maps to predictions provided by a recent semi-analytic model, which is implanted within the dark-matter Millennium Simulation. We analyse galaxies with stellar masses between $10^9-10^{11}\,{\rm M}_\odot$ in two photometric redshift bins, for lens redshifts $z\lesssim0.6$, focusing on pairs inside groups and clusters. To allow us a better interpretation of the maps, we discuss the impact of chance pairs, i.e., galaxy pairs that appear close to each other in projection only. Our tests with synthetic data demonstrate that the patterns observed in the maps are essentially produced by correlated pairs that are close in redshift ($\Delta z\lesssim5\times10^{-3}$). We also verify the excellent accuracy of the map estimators. In an application to the galaxy samples in the CFHTLenS, we obtain a $3\sigma-6\sigma$ significant detection of the excess mass and an overall good agreement with the galaxy model predictions. There are, however, a few localised spots in the maps where the observational data disagrees with the model predictions on a $\approx3.5\sigma$ confidence level. Although we have no strong indications for systematic errors in the maps, this disagreement may be related to the residual B-mode pattern observed in the average of all maps. Alternatively, misaligned galaxy pairs inside dark matter halos or lensing by a misaligned distribution of the intra-cluster gas might also cause the unanticipated bulge in the distribution of the excess mass between lens pairs.