Heating the intra-cluster medium perpendicular to the jets axis

TL;DR

Simulations show that mixing of shocked jet material with the intra-cluster medium efficiently heats the gas perpendicular to the jets' axis, sustaining heating long after jet activity ceases and impacting magnetic fields and galaxy evolution.

Contribution

This study demonstrates that mixing, rather than shock heating, is the dominant process heating the intra-cluster medium perpendicular to jets in galaxy clusters.

Findings

Mixing heats the ICM efficiently up to ~10 kpc and beyond.

Heating persists for over 10^8 years after jet activity ends.

Mixing influences magnetic fields and supports cold feedback mechanisms.

Abstract

By simulating jet-inflated bubbles in cooling flows with the PLUTO hydrodynamic code we show that mixing of high entropy shocked jet's material with the intra-cluster medium (ICM) is the major heating process perpendicular to the jets' axis. Heating by the forward shock is not significant. The mixing is very efficient in heating the ICM in all directions, to distances of ~10kpc and more. Although the jets are active for a time period of only 20 Myr, the mixing and heating near the equatorial plane, as well as along the symmetry axis, continues to counter radiative cooling for times of >10^8 yr after the jets have ceased to exist. We discuss some possible implications of the results. (i) The vigorous mixing is expected to entangle magnetic field lines, hence to suppress any global heat conduction in the ICM near the center. (ii) The vigorous mixing forms multi-phase ICM in the inner cluster regions, where the coolest parcels of gas will eventually cool first, flow inward, and feed the active galactic nucleus to set the next jet-activity episode. This further supports the cold feedback mechanism. (iii) In cases where the medium outside the region of r~10kpc is not as dense as in groups and clusters of galaxies, like during the process of galaxy formation, the forward shock and the high pressure of the shocked jets' material might expel gas from the system.