Creation of the X‐Ray Cavity Jet and Its Radio Lobe in M87/Virgo with Cosmic Rays: Relevance to Relic Radio Sources

Abstract

Young cavities in the X-ray emitting hot gas in galaxy clusters are often filled with radio synchrotron emission and it is widely thought that the cavities are inflated by these cosmic rays. At a later stage of its evolution, when the cavity becomes buoyant, the converging flow of gas beneath the cavity results in a filament of thermal gas, a cavity jet, that moves radially outward at large subsonic velocities. As the cavity jet forms, the cosmic ray electrons may diffuse through the cavity walls, filling a large volume surrounding the cavity jet, as observed in M87/Virgo and elsewhere, sometimes referred to as relic radio sources. We compute the combined evolution of cosmic rays, cavities and cavity jets. The observed pattern in M87/Virgo can be reached in 100 Myrs, matching the synchrotron age of the extended radio source. A 20-30 kpc long cavity jet is surrounded by a quasi-spherical radio lobe 40 kpc in diameter, but the initial cavity has disappeared. At later times the cavity jet will fall back to the origin, leaving only the extended radio source. The combined jet-lobe evolution in M87/Virgo requires a total cosmic ray energy that is more than 10 times larger than that usually assumed, 4PV.