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The diffuse plasma inside clusters of galaxies has X-ray emittingtemperatures of a few keV. The physical mechanisms that heat this intraclustermedium (ICM) to such temperatures include the accretion shock at the peripheryof a galaxy cluster, the shocks driven by merger events, as well as a somewhatoverlooked mechanism -- the dissipation of intracluster turbulent motions. Westudy the relative role of these heating mechanisms using galaxy clusters inLagrangian tracer particle re-simulations of the Omega500 cosmologicalsimulation. We adopt a novel analysis method of decomposing the temperatureincrease at each time step into the contribution from dissipative heating andthat from adiabatic heating. In the high-resolution spatial-temporal map ofthese heating rates, merger tracks are clearly visible, demonstrating thedominant role of merger events in heating the ICM. The dissipative heatingcontributed by each merger event is extended in time and also occurs in therarefaction regions, suggesting the importance of heating by the dissipation ofmerger-induced turbulence. Quantitative analysis shows that turbulence heating,rather than direct heating at merger shocks, dominates the temperature increaseof the ICM, especially at inner radii $r < r_{\rm 500c}$. In addition, we findthat many merger shocks can propagate with almost constant velocity to verylarge radii $r \gg r_{\rm 500c}$, some even reach and join with the accretionshock and becoming the outer boundary of the ICM. Altogether, these resultssuggest that the ICM is heated more in an `inside-out' fashion rather than`outside-in' as depicted in the classical smooth accretion picture.

Dynamical heating of the X-ray emitting intracluster medium: the roles of merger shocks and turbulence dissipation