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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

Effects of Viscosity on Sloshing Cold Fronts in Galaxy Clusters

  • Ming-Hsueh Hsieh1
  • H-Y Karen Yang1,2,3
  • John ZuHone4
4 affiliations
  1. 1Institute of Astronomy, National Tsing Hua University , Hsinchu 30013, Taiwan
  2. 2Center for Informatics and Computation in Astronomy, National Tsing Hua University , Hsinchu 30013, Taiwan
  3. 3Physics Division, National Center for Theoretical Sciences , Taipei 106017, Taiwan
  4. 4Center for Astrophysics | Harvard, and Smithsonian , 60 Garden Street, Cambridge, MA 02138 ,
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Abstract

The viscous properties of the intracluster medium (ICM) remain poorly constrained. Cold fronts—sharp discontinuities formed during cluster mergers—offer a potential avenue to probe the effective viscosity of the ICM. Velocity shear across these fronts should generate Kelvin–Helmholtz instabilities (KHI), unless viscosity or magnetic tension suppresses them. We perform cluster merger simulations incorporating four ICM viscosity models: (A) inviscid, (B) isotropic Spitzer viscosity, (C) anisotropic Braginskii viscosity, and (D) Braginskii viscosity limited by microinstabilities. The isotropic Spitzer viscosity (case B) strongly suppresses KHI, producing smooth cold front surfaces, while the inviscid (A) and microinstability-limited (D) cases show prominent ripples. The Braginskii case (C) yields intermediate suppression. We also vary the plasma β parameter (β ≈ 100 and 1600) to examine how a changing magnetic field strength affects the results. Stronger magnetic fields further suppress KHI, leading to smoother fronts and reduced differences between different viscosity models, while also widening the range of permitted pressure anisotropies when microinstability-based limiters are present. These results indicate that both viscosity and magnetic fields play crucial roles in stabilising sloshing cold fronts in galaxy clusters.

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Cite

BibTeXRIS
BibTeX
@article{hsieh2026effects,
  title = {{Effects of Viscosity on Sloshing Cold Fronts in Galaxy Clusters}},
  author = {Ming-Hsueh Hsieh and H-Y Karen Yang and John ZuHone},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag1937},
  url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1937/8914599},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Effects of Viscosity on Sloshing Cold Fronts in Galaxy Clusters
AU  - Ming-Hsueh Hsieh
AU  - H-Y Karen Yang
AU  - John ZuHone
PY  - 2026
DA  - 2026/10/13
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1937
UR  - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1937/8914599
AB  - The viscous properties of the intracluster medium (ICM) remain poorly constrained. Cold fronts—sharp discontinuities formed during cluster mergers—offer a potential avenue to probe the effective viscosity of the ICM. Velocity shear across these fronts should generate Kelvin–Helmholtz instabilities (KHI), unless viscosity or magnetic tension suppresses them. We perform cluster merger simulations incorporating four ICM viscosity models: (A) inviscid, (B) isotropic Spitzer viscosity, (C) anisotropic Braginskii viscosity, and (D) Braginskii viscosity limited by microinstabilities. The isotropic Spitzer viscosity (case B) strongly suppresses KHI, producing smooth cold front surfaces, while the inviscid (A) and microinstability-limited (D) cases show prominent ripples. The Braginskii case (C) yields intermediate suppression. We also vary the plasma β parameter (β ≈ 100 and 1600) to examine how a changing magnetic field strength affects the results. Stronger magnetic fields further suppress KHI, leading to smoother fronts and reduced differences between different viscosity models, while also widening the range of permitted pressure anisotropies when microinstability-based limiters are present. These results indicate that both viscosity and magnetic fields play crucial roles in stabilising sloshing cold fronts in galaxy clusters.
SN  - 0035-8711
SN  - 1365-2966
ER  -