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

¹ Laboratoire d’Astrophysique École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
e-mail: danuta.paraficz@epfl.ch
² Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
³ Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, UMR 5574, 69230 Saint-Genis-Laval, France
⁴ Physics Department, University of Alabama in Huntsville, Huntsville, AL 35899, USA

Received: 14 December 2015
Accepted: 11 August 2016

Abstract

Aims. 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).

Methods. 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.

Results. 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 × 10¹⁴M_⊙ within a 250 kpc radial aperture.