Oral Presentation

On the Importance of Internally-subsonic Jets in Radio-mode AGN Feedback

Author(s): Fulai Guo (SHAO)

Presenter: Fulai Guo (Shanghai Astronomical Observatory)

Black hole jets and feedback play a key role in the evolution of hot gas and massive elliptical galaxies in galaxy groups and clusters. However, little is known about the internal components and deceleration processes of AGN jets moving from black hole vicinities to kpc and larger scales. Large-scale jet simulations almost always initiate jets faster than their internal sound speeds. Here we argue for the first time for the importance of internally-subsonic jets on kpc scales in AGN feedback. They produce strong backflows at the working surface, resulting in bottom-wide young X-ray cavities in the ICM, while internally-supersonic jets produce center-wide or top-wide young X-ray cavities. Due to lower jet momentum, cavities produced by internally-subsonic jets move much slower than those by internally-supersonic jets, more consistent with buoyantly-rising X-ray cavities observed in many galaxy clusters. Internally-subsonic jets are thus expected to heat cool cores of galaxy clusters more efficiently than internally-supersonic jets. The internal Mach number corresponds to the energy content of AGN jets, and internally-subsonic jets are energetically dominated by non-kinetic energy, such as thermal energy, cosmic rays, or magnetic fields.