MC2: Dynamical Analysis of the Merging Galaxy Cluster MACS J1149.5+2223

N. Golovich, W. A. Dawson, D. Wittman, G. A. Ogrean, R. J. van Weeren, A. Bonafede

Abstract
We present an analysis of the merging cluster MACS J1149.5+2223 using archival imaging from Subaru/Suprime-Cam and multi-object spectroscopy from Keck/DEIMOS and Gemini/GMOS. We employ two- and three-dimensional substructure tests and determine that MACS J1149.5+2223 is composed of two separate mergers among three subclusters occurring ̃1 Gyr apart. The primary merger gives rise to elongated X-ray morphology and a radio relic in the southeast. The brightest cluster galaxy is a member of the northern subcluster of the primary merger. This subcluster is very massive ({16.7}_-1.60^+1.25× {10}¹⁴ {M}_☉ ). The southern subcluster is also very massive ({10.8}_-3.54^+3.37× {10}¹⁴ {M}_☉ ), yet it lacks an associated X-ray surface brightness peak, and it has been unidentified previously despite the detailed study of this Frontier Field cluster. A secondary merger is occurring in the north along the line of sight (LOS) with a third, less massive subcluster ({1.20}_-0.34^+0.19× {10}¹⁴ {M}_☉ ). We perform a Monte Carlo dynamical analysis on the main merger and estimate a collision speed at pericenter of {2770}_-310⁺⁶¹⁰ km s^-1. We show the merger to be returning from apocenter with core passage occurring {1.16}_-0.25^+0.50 Gyr before the observed state. We identify the LOS merging subcluster in a strong lensing analysis in the literature and show that it is likely bound to MACS J1149 despite having reached an extreme collision velocity of ̃4000 km s^-1.

Keywords
galaxies: clusters: individual: MACS J1149.5+2223, galaxies: distances and redshifts, large-scale structure of universe

The Astrophysical Journal
October 2016

DOI: 10.3847/0004-637X/831/1/110
ADS Bibliographic code: 2016ApJ...831..110G