Active galactic nuclei jets simulated with smoothed particle hydrodynamics

Abstract

Active galactic nuclei (AGN) jets play an important role as a feedback mechanism that quenches the growth of massive galaxies. These jets have so far been simulated almost exclusively with grid-based codes. In this work we present results from hydrodynamical tests of AGN jets simulated with the SWIFT code and its implementation of smoothed particle hydrodynamics (SPH). We reach numerical resolutions of more than a million particles per jet, unprecedented for an SPH code. In all cases we find broad agreement between our jets and theoretical predictions for the jet and lobe lengths and widths. At very low resolutions, typical of lowresolution cosmological simulations (𝑚 gas ≈ 10 7 M ), the shape of the lobes is close to selfsimilar ones at a level of 15% accuracy. This indicates that the basics of jet lobe physics can be captured even at such resolutions (≈ 500 particles per jet). The jets first evolve ballistically, and then transition to a self-similar phase, during which the kinetic and thermal energies in the lobes and the shocked ambient medium are constant fractions of the total injected energy. In our standard simulation, two thirds of the initially injected energy is transferred to the ambient medium by the point the jets are turned off, mainly through a bow shock. Of that, three quarters is in thermal form, indicating that the bow shock thermalizes efficiently. We find that jet launching velocity and power, in addition to determining the temperature, mass and overall length of the jets, also play an important role in the resolution of the jets.

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