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A Brush with Turbulence: Probing the ICM Dynamics in the Merging Toothbrush Cluster using XRISM

Anjali MadangarliLorentz Institute for Theoretical Physics , Leiden University , PO Box 9506 , NL-2300 RA Leiden , The NetherlandsAurora SimionescuHuub RöttgeringLeiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The NetherlandsAnwesh MajumderSRON , Space Research Organisation Netherlands , Niels Bohrweg 4 , 2333 CA Leiden , The NetherlandsSoeda HaruseDepartment of Physics , Nagoya University , Aichi 464-8602 , JapanKazuhiro NakazawaKMI , Nagoya University , Aichi 464-8602 , JapanYuusuke UchidaInstitute of Space and Astronautical Science (ISAS) , Japan Aerospace Exploration Agency (JAXA) , Kanagawa 252-5210 , JapanDaisuke ItoDepartment of Physics , Nagoya University , Aichi 464-8602 , JapanGianfranco BrunettiNational Institute for AstrophysicsReinout van WeerenLeiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The NetherlandsCongyao ZhangDepartment of Theoretical Physics and Astrophysics , Faculty of Science , Masaryk University , Brno 61137 , CzechiaK. RajpurohitCenter for Astrophysics Harvard & Smithsonian , 60 Garden Street , Cambridge , MA 02138 , USAPriyanka ChakrabortyDepartment of Physics , University of Arkansas Main Campus , 825 W Dickson Street Fayetteville , AR 72701 , USAHiroki AkamatsuQUP , KEK , 1-1 Oho , Tsukuba , Ibaraki 300-3256 , Japan

2026

Ochiq kirishYashil

ABI

Annotatsiya

The Toothbrush Cluster (1RXS J0603.3+4214) is known for its northern radio relic, radio halo, and highly disturbed X-ray morphology. It shows features of both shock-driven and turbulent reacceleration, the latter of which is invoked to explain its radio halo. However, how kinetic energy from the merger is distributed into gas motions across spatial scales remains unclear. We probe the intracluster medium (ICM) dynamics in the southern, X-ray-brightest region of the cluster using a 167 ks XRISM/Resolve observation. We conduct both full-array and quadrant sub-array analyses by fitting the spectra with single and multi-component thermal models in the 3-8 keV band. The full-array spectrum favours two ICM components with a transonic line-of-sight (LOS) velocity difference of $Δv_{\mathrm{bulk}}=1635^{+165}_{-110}$ km s$^{-1}$, while the velocity dispersions are much lower, at $σ_{v,1\mathrm{D}}\sim$245-310 km s$^{-1}$. The sub-array analysis likewise reveals multiple components in at least three quadrants, with LOS bulk velocities ranging from $-2520^{+295}_{-230}$ to $+930^{+70}_{-110}$ km s$^{-1}$. The velocity dispersions remain modest at $\sim$215 km s$^{-1}$, corresponding to a turbulent pressure support of about 3-6% on scales dominating the observed line broadening. Cooler gas is detected in the NE and SW, with $kT_{\mathrm{NE}}=3.13^{+0.33}_{-0.30}$ keV and $kT_{\mathrm{SW}}=2.32^{+0.43}_{-0.37}$ keV, likely associated with a third, northern subcluster identified in weak-lensing and optical studies. Our results indicate a complex ICM kinematic structure, with evidence for at least three subclusters exhibiting supersonic bulk velocity offsets and much smaller velocity dispersions. This shows that the merger geometry has a significant line-of-sight component and may indicate that the cluster collision is relatively young, with the turbulent cascade not yet fully established.

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DOI: 10.48550/arxiv.2610.05351

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