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Modeling AGN Feedback in Cool-Core Clusters: The Formation of Cold Clumps

We perform high-resolution (15-30 pc) adaptive mesh simulations to study the impact of momentum-driven AGN feedback in cool-core clusters, focusing in this paper on the formation of cold clumps. The feedback is jet-driven with an energy determined by the amount of cold gas within 500 pc of the SMBH. When the intra-cluster medium (ICM) in the core of the cluster becomes marginally stable to radiative cooling, with the thermal instability to the free-fall timescale ratio t_{TI}/t_{ff} < 3-10, cold clumps of gas start to form along the propagation direction of the AGN jets. By tracing the particles in the simulations, we find that these cold clumps originate from low entropy (but still hot) gas that is accelerated by the jet to outward radial velocities of a few hundred km/s. This gas is out of hydrostatic equilibrium and so can cool. The clumps then grow larger as they decelerate and fall towards the center of the cluster, eventually being accreted onto the super-massive black hole. The general morphology, spatial distribution and estimated Hα morphology of the clumps are in reasonable agreement with observations, although we do not fully replicate the filamentary morphology of the clumps seen in the observations, probably due to missing physics.