A large-scale shock surrounding a powerful radio galaxy

TL;DR

This study reports the detection of a large-scale shock around a powerful radio galaxy using Chandra X-ray observations, revealing insights into the shock dynamics, energy transfer, and pressure balance in the galaxy's environment.

Contribution

First detection of a large-scale spheroidal shock around an FRII radio galaxy with detailed measurements of shock properties and energy transfer.

Findings

Shock Mach number ~1.7 indicating a mildly supersonic shock

Detection of cavities aligned with radio lobes, second such case for an FRII

Estimated energy transfer to environment at least 8.2 x 10^60 ergs

Abstract

We report the Chandra detection of a large-scale shock, on scales of 200 kpc, in the cluster surrounding the powerful radio galaxy 3C 444 (PKS 2211-17). Our 20-ks Chandra observation allows us to identify a clear surface brightness drop around the outer edge of the radio galaxy, which is likely to correspond to a spheroidal shock propagating into the intracluster medium. We measure a temperature jump across the surface brightness drop of a factor ~1.7, which corresponds to a Mach number of ~1.7. This is likely to be an underestimate due to the need to average over a fairly large region when measuring the temperature of the post-shock gas. We also detect clear cavities corresponding to the positions of the radio lobes, which is only the second such detection associated with an FRII radio galaxy. We estimate that the total energy transferred to the environment is at least 8.2 x 10^60 ergs, corresponding to a jet power of >2.2 x 10^45 ergs s^-1 (assuming a timescale based on the measured shock speed). We also compare the external pressure acting on the lobes with the internal pressure under various assumptions, and conclude that a significant contribution from protons is required.