The return of the merging galaxy subclusters of El Gordo?

Karen Y. Ng, William A. Dawson, D. Wittman, M. James Jee, John P. Hughes, Felipe Menanteau, Cristóbal Sifón

Research output: Contribution to journalArticlepeer-review

30 Citations (Scopus)


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. 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°±911. We find the relative 3D merger speed of El Gordo to be 2400 ±400200 km s-1 at pericentre. The two possible estimates of the time since pericentre (TSP) are 0.46±0.090.16 and 0.91±0.220.39 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. 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.

Original languageEnglish
Pages (from-to)1531-1549
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 2015 Aug 6

Bibliographical note

Publisher Copyright:
© 2015 The Authors.

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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