Title: The return of the merging galaxy subclusters of El Gordo?

Abstract

Merging galaxy clusters with radio relics provide rare insights to the merger dynamics as the relics are created by the violent merger process. We demonstrate one of the first uses of the properties of the radio relic to reduce the uncertainties of the dynamical variables and determine the three-dimensional (3D) configuration of a cluster merger, ACT-CL J0102-4915, nicknamed El Gordo. From the double radio relic observation and the X-ray observation of a comet-like gas morphology induced by motion of the cool core, it is widely believed that El Gordo is observed shortly after the first core passage of the subclusters. Here, we employ a Monte Carlo simulation to investigate the 3D configuration and dynamics of El Gordo. Using the polarization fraction of the radio relic, we constrain the estimate of the angle between the plane of the sky and the merger axis to be α=21°± $$9\atop{11}$$. We find the relative 3D merger speed of El Gordo to be 2400 ± $$400\atop{200}$$ km s^-1 at pericentre. The two possible estimates of the time since pericentre (TSP) are 0.46 ± $$0.09\atop{0.16}$$ and 0.91± $$0.22\atop{0.39}$$ Gyr for the outgoing and returning scenario, respectively. We put our estimates of the TSP into context by showing that if the time-averaged shock velocity is approximately equal to or smaller than the pericentre velocity of the corresponding subcluster in the centre-of-mass frame, the two subclusters are more likely to be moving towards, rather than away, from each other, post apocentre. Finally, we compare and contrast the merger scenario of El Gordo with that of the Bullet Cluster, and show that this late-stage merging scenario explains why the south-east (SE) dark matter lensing peak of El Gordo is closer to the merger centre than the SE cool core.

Authors:

Ng, Karen Y. ^[1]; Dawson, William A. ^[2]; Wittman, D. ^[1]; Jee, M. James ^[1]; Hughes, John P. ^[3]; Menanteau, Felipe ^[4]; Sifon, Cristobal ^[5]

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+ Show Author Affiliations

1. Univ. of California, Davis, CA (United States). Dept. of Physics
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
3. Rutgers Univ., Piscataway, NJ (United States). Dept. of Physics & Astronomy
4. Univ. of Illinois, Urbana-Champaign, IL (United States). National Center for Supercomputing Applications (NCSA), Dept. of Astronomy
5. Leiden Univ. (Netherlands). Leiden Observatory

Publication Date:

Tue Aug 25 00:00:00 EDT 2015

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1430968

Report Number(s):

LLNL-JRNL-737795
Journal ID: ISSN 0035-8711; TRN: US1803007

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Monthly Notices of the Royal Astronomical Society

Additional Journal Information:

Journal Volume: 453; Journal Issue: 2; Journal ID: ISSN 0035-8711

Publisher:

Royal Astronomical Society

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; methods: statistical, galaxies: clusters: individual (ACT-CL J0102-4915), galaxies: high-redshift, cosmology: observations, dark matter