Galaxy cluster mergers are rich sources of information to test cluster astrophysics and cosmology. However, cluster mergers produce complex projected signals that are difficult to interpret physically from individual observational probes. Multi-probe constraints on the gas and dark matter (DM) cluster components are necessary to infer merger parameters that are otherwise degenerate. We present Improved Constraints on Mergers with SZ, Hydrodynamical simulations, Optical, and X-ray (ICM-SHOX), a systematic framework to jointly infer multiple merger parameters quantitatively via a pipeline that directly compares a novel combination of multi-probe observables to mock observables derived from hydrodynamical simulations. We report a first application of the ICM-SHOX pipeline to MACS J0018.5+1626, wherein we systematically examine simulated snapshots characterized by a wide range of initial parameters to constrain the MACS J0018.5+1626 merger geometry. We constrain the epoch of MACS J0018.5+1626 to the range 0–60 Myr post-pericenter passage, and the viewing angle is inclined ≈27°–40° from the merger axis. We obtain constraints for the impact parameter (≲250 kpc), mass ratio (≈1.5–3.0), and initial relative velocity when the clusters are separated by 3 Mpc (≈1700–3000 km s−1). The primary and secondary clusters initially (at 3 Mpc) have gas distributions that are moderately and strongly disturbed, respectively. We discover a velocity space decoupling of the DM and gas distributions in MACS J0018.5+1626, traced by cluster-member galaxy velocities and the kinematic Sunyaev–Zel'dovich effect, respectively. Our simulations indicate this decoupling is dependent on the different collisional properties of the two distributions for particular merger epochs, geometries, and viewing angles.
ICM-SHOX. I. Methodology Overview and Discovery of a Gas–Dark Matter Velocity Decoupling in the MACS J0018.5+1626 Merger
Abstract
Copyright and License
© 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology (Caltech), the University of California, and the National Aeronautics and Space Administration (NASA). The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
The X-ray observations in this analysis were obtained from the Chandra Data Archive. The hydrodynamical simulations were run on the Pleiades supercomputer at NASA/Ames Research Center. The simulation post-processing computations were conducted in the Resnick High Performance Computing Center, a facility supported by the Resnick Sustainability Institute at Caltech.
E.M.S. acknowledges support from a National Science Foundation Graduate Research Fellowship (NSF GRFP) under grant No. DGE-1745301, the Wallace L. W. Sargent Graduate Fellowship at Caltech, and NSF/AST-2206082. J.S. acknowledges support from NSF/AST-2206082. J.A.Z. and U.C. are funded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. E.B. acknowledges support from NSF/AST-2206083. A.Z. acknowledges support by grant No. 2020750 from the United States-Israel Binational Science Foundation (BSF) and grant No. 2109066 from the United States NSF, and by the Ministry of Science & Technology, Israel. T.M. acknowledges support from the AtLAST project, which has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 951815. A.M. thanks support from Consejo Nacional de Humanidades Ciencias y Technologías (CONAHCYT) project A1-S-45680. We thank the anonymous reviewer for the detailed comments, which helped improve this manuscript.
Facilities
Keck/DEIMOS - , CXO - Chandra X-ray Observatory satellite, CSO - Caltech Submillimeter Observatory, (installed on the 10 m Atacama Submillimeter Telescope Experiment) - Atacama Submillimeter Telescope Experiment, Planck - European Space Agency's Planck space observatory, HST - Hubble Space Telescope satellite
Software References
GAMER-2 (Schive et al. 2018), Xspec 12.12.0 (Arnaud 1996), yt (Turk et al. 2011), pyXSIM (ZuHone & Hallman 2016), SOXS (ZuHone et al. 2023), mpi4py (Dalcin & Fang 2021), CIAO (Fruscione et al. 2006), PypeIt (Prochaska et al. 2020), spec2d (Cooper et al. 2012; Newman et al. 2013), SpecPro (Masters & Capak 2011), Pumpkin (Rhea et al. 2020), Astropy (Astropy Collaboration et al. 2013, 2018), NumPy (van der Walt et al. 2011; Harris et al. 2020), Matplotlib (Hunter 2007), lmfit (Newville et al. 2014), Colossus (Diemer 2018), contbin (Sanders 2006), scikit-image; (van der Walt et al. 2014)
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Additional details
- ISSN
- 1538-4357
- W. M. Keck Foundation
- Resnick Sustainability Institute
- National Science Foundation
- NSF Graduate Research Fellowship DGE-1745301
- California Institute of Technology
- Wallace L. W. Sargent Graduate Fellowship
- National Science Foundation
- AST-2206082
- National Aeronautics and Space Administration
- NAS8-03060
- National Science Foundation
- AST-2206083
- United States-Israel Binational Science Foundation
- 2020750
- National Science Foundation
- AST-2109066
- Ministry of Science, Technology and Space
- European Research Council
- 951815
- Consejo Nacional de Humanidades, Ciencias y Tecnologías
- A1-S-45680
- Caltech groups
- Astronomy Department, Resnick Sustainability Institute