The Bullet cluster at its best: weighing stars, gas and dark matter

TL;DR

This study provides a highly precise strong lensing mass reconstruction of the Bullet cluster, explicitly modeling gas, stars, and dark matter, confirming spatial offsets and quantifying mass fractions with improved accuracy.

Contribution

It introduces a revised mass model incorporating intra-cluster gas, cluster galaxies, and dark matter, with enhanced constraints and Bayesian evidence favoring the gas-inclusive model.

Findings

The mass model has an RMS of 0.158" matching HST resolution.

Confirms spatial offset between X-ray gas and dark matter peaks.

Galaxy halos contribute approximately 11% to total mass.

Abstract

We present a new strong lensing mass reconstruction of the Bullet cluster (1E 0657-56) at z=0.296, based on WFC3 and ACS HST imaging and VLT/FORS2 spectroscopy. The strong lensing constraints underwent substantial revision compared to previously published analysis, there are now 14 (six new and eight previously known) multiply-imaged systems, of which three have spectroscopically confirmed redshifts (including one newly measured from this work). The reconstructed mass distribution explicitly included the combination of three mass components: i) the intra-cluster gas mass derived from X-ray observation, ii) the cluster galaxies modeled by their fundamental plane scaling relations and iii) dark matter. The model that includes the intra-cluster gas is the one with the best Bayesian evidence. This model has a total RMS value of 0.158" between the predicted and measured image positions for the 14 multiple images considered. The proximity of the total RMS to resolution of HST/WFC3 and ACS (0.07-0.15" FWHM) demonstrates the excellent precision of our mass model. The derived mass model confirms the spatial offset between the X-ray gas and dark matter peaks. The fraction of the galaxy halos mass to total mass is found to be f_s=11+/-5% for a total mass of 2.5+/-0.1 x 10^14 solar mass within a 250 kpc radial aperture.