The Three Hundred: Cluster Dynamical States and Relaxation Time Scale

Bowei Zhang*, Weiguang Cui*, Yuhuan Wang, Romeel Dave, Marco De Petris

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We introduce a new parameter λDS to quantify the dynamical state of galaxy clusters and test it using simulations from The Three Hundred cluster zoom suite. λDS is a combination of three previously used dynamical state measures, namely virial ratio, centre of mass offset, and substructure mass fraction, crafted to assume a double-Gaussian distribution, thereby yielding a natural division between relaxed and unrelaxed clusters where the Gaussians cross. Using dark matter-only simulations, we identify the optimal separator to be λDS = 3.424. We test this same criterion on two sets of fully hydrodynamical The Three Hundred runs (Gadget-X and GIZMO-SIMBA), and find only a weak dependence on the input baryonic physics. We correlate the evolution of λDS with the mass accretion history and find that halo mass changes of ΔM200M200≲0.12 do not typically alter the dynamical state. We examine the relaxation period, defined as the time taken to return to relaxation after becoming disturbed, and find a correlation between this relaxation period and the strength of halo mass change ΔM200M200⁠. By fitting this correlation, we show that the relaxation period can be estimated from ΔM200M200 (even for multiple mass accretion events) with good accuracy.
Original languageEnglish
Pages (from-to)26-38
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date1 Aug 2022
Publication statusPublished - 1 Oct 2022

Keywords / Materials (for Non-textual outputs)

  • astro-ph.CO
  • astro-ph.GA


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