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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× 1014 M). The southern subcluster is also very massive (10.8-3.54+3.37× 1014 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× 1014 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
Volume 831, Number 1
2016 November

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia