# Joining X-ray to lensing: an accurate combined analysis of MACS J0416.1$-$2403

## TL;DR

This paper introduces a new combined analysis method for X-ray and gravitational lensing data to improve dark matter distribution mapping in galaxy clusters, demonstrated on MACS J0416.1$-$2403.

## Contribution

The novel technique integrates X-ray gas data into lensing models, enabling separation of collisional and collisionless mass components for more accurate dark matter profiles.

## Key findings

- Projected gas to total mass fraction is about 10% at 350 kpc.
- Dark matter mass profile differs significantly from traditional models.
- Dark matter to total mass ratio remains nearly constant out to 350 kpc.

## Abstract

We present a novel approach for a combined analysis of X-ray and gravitational lensing data and apply this technique to the merging galaxy cluster MACS J0416.1$-$2403. The method exploits the information on the intracluster gas distribution that comes from a fit of the X-ray surface brightness, and then includes the hot gas as a fixed mass component in the strong lensing analysis. With our new technique, we can separate the collisional from the collision-less diffuse mass components, thus obtaining a more accurate reconstruction of the dark matter distribution in the core of a cluster. We introduce an analytical description of the X-ray emission coming from a set of dual Pseudo-Isothermal Elliptical (dPIE) mass distributions, which can be directly used in most lensing softwares. By combining \emph{Chandra} observations with Hubble Frontier Fields imaging and MUSE spectroscopy in MACS J0416.1$-$2403, we measure a projected gas over total mass fraction of approximately $10\%$ at $350$ kpc from the cluster center. Compared to the results of a more traditional cluster mass model (diffuse halos plus member galaxies), we find a significant difference in the cumulative projected mass profile of the dark matter component and that the dark matter to total mass fraction is almost constant, out to more than $350$ kpc. In the coming era of large surveys, these results show the need of multi-probe analyses for detailed dark matter studies in galaxy clusters.