# The galaxy-subhalo connection in low-redshift galaxy clusters from weak gravitational lensing

## TL;DR

This study measures the connection between satellite galaxy subhalos and their stellar masses in low-redshift clusters using weak gravitational lensing, correcting for observational biases to reveal the subhalo-stellar mass relation.

## Contribution

It provides the first direct measurement of the subhalo-to-stellar-mass relation in galaxy clusters, accounting for shape measurement biases and defining subhalo mass based on bound mass.

## Key findings

- Subhalo-to-stellar-mass relation characterized with a power-law fit.
- Subhalo masses are about 50% of central galaxy masses at certain stellar masses.
- Evidence suggests tidal stripping effects near the cluster scale radius.

## Abstract

We measure the gravitational lensing signal around satellite galaxies in a sample of galaxy clusters at $z<0.15$ by combining high-quality imaging data from the Canada-France-Hawaii Telescope with a large sample of spectroscopically-confirmed cluster members. We use extensive image simulations to assess the accuracy of shape measurements of faint, background sources in the vicinity of bright satellite galaxies. We find a small but significant bias, as light from the lenses makes the shapes of background galaxies appear radially aligned with the lens. We account for this bias by applying a correction that depends on both lens size and magnitude. We also correct for contamination of the source sample by cluster members. We use a physically-motivated definition of subhalo mass, namely the mass bound to the subhalo, $m_\mathrm{bg}$, similar to definitions used by common subhalo finders in numerical simulations. Binning the satellites by stellar mass we provide a direct measurement of the subhalo-to-stellar-mass relation, $\log m_\mathrm{bg}/\mathrm{M}_\odot = (11.54\pm0.05) + (0.95\pm0.10)\log[m_\star/(2\times10^{10}\mathrm{M}_\odot)]$. This best-fitting relation implies that, at a stellar mass $m_\star\sim3\times10^{10}\,\mathrm{M}_\odot$, subhalo masses are roughly 50 per cent of those of central galaxies, and this fraction decreases at higher stellar masses. We find some evidence for a sharp change in the total-to-stellar mass ratio around the clusters' scale radius, which could be interpreted as galaxies within the scale radius having suffered more strongly from tidal stripping, but remain cautious regarding this interpretation.