The shape of galaxy dark matter halos in massive galaxy clusters: Insights from strong gravitational lensing

TL;DR

This study utilizes strong gravitational lensing data from the Hubble Space Telescope and VLT/MUSE to analyze dark matter distribution in galaxy clusters, revealing potential alignments and misalignments between dark matter and stars, and improving mass models.

Contribution

It introduces a method to constrain dark matter distribution in galaxy clusters using detailed lensing data, enhancing mass modeling accuracy and providing insights into dark matter properties.

Findings

Tentative evidence of dark matter ellipticity similar to stars

Dark matter and baryonic halos often misaligned

Model improvement by 35% when allowing non-coincident halos

Abstract

We assess how much unused strong lensing information is available in the deep \emph{Hubble Space Telescope} imaging and VLT/MUSE spectroscopy of the \emph{Frontier Field} clusters. As a pilot study, we analyse galaxy cluster MACS\,J0416.1-2403 ($z$$=$$0.397$, $M(R<200\,{\rm kpc})$$=$$1.6$$\times$$10^{14}\msun$), which has 141 multiple images with spectroscopic redshifts. We find that many additional parameters in a cluster mass model can be constrained, and that adding even small amounts of extra freedom to a model can dramatically improve its figures of merit. We use this information to constrain the distribution of dark matter around cluster member galaxies, simultaneously with the cluster's large-scale mass distribution. We find tentative evidence that some galaxies' dark matter has surprisingly similar ellipticity to their stars (unlike in the field, where it is more spherical), but that its orientation is often misaligned. When non-coincident dark matter and baryonic halos are allowed, the model improves by 35\%. This technique may provide a new way to investigate the processes and timescales on which dark matter is stripped from galaxies as they fall into a massive cluster. Our preliminary conclusions will be made more robust by analysing the remaining five \emph{Frontier Field} clusters.