# Jet-driven bubbles in Fanaroff-Riley type I sources

## TL;DR

This paper investigates how choked relativistic jets in Fanaroff-Riley type I sources create bipolar bubbles, constraining jet properties and suggesting jet collimation mechanisms influence galaxy cluster radio morphology.

## Contribution

It provides new constraints on the jet quenching radius and collimation in FRI sources, linking jet properties to observed bubble structures and morphology.

## Key findings

- Jet quenching radius typically around 10 kpc.
- Jets must be tightly collimated with angles less than 2° to reach this radius.
- Degeneracy between initial jet opening angle and activity duration.

## Abstract

Observations of several Fanaroff-Riley (FR) type I sources reveal outflowing bipolar bubbles of hot gas surrounded by a weak forward shock. We consider the possibility that these bubbles were driven by choked relativistic jets which failed to penetrate the ambient intracluster medium (ICM). Using new results on choked jets linking the geometry of the forward shock to the jet properties, we infer robust limits on the radius $R_{ch}$ at which the jet was quenched in 5 well-studied FRI sources, finding typically $R_{ch}\sim 10$ kpc. We further show that, in order to reach this radius in less than the current age of the system, the jet must have been tightly collimated, with the jet head subtending an angle of $\theta_h < 2^\circ$. The ambient pressure is not high enough to explain this collimation, suggesting that the jet was collimated by interaction with its own cocoon. Although the choking radius is well-constrained, we find a degeneracy between the initial jet opening angle before collimation, $\theta_0$, and the duration of jet activity, $t_b$, with $(t_b/1\rm{Myr})(\theta_0/5^\circ)^{-2} \sim 0.1$. We speculate that the working time and/or opening angle of the jet may be important factors contributing to the FR type I/type II morphology in galaxy clusters, with short-lived or wide jets being choked to form bipolar bubbles filled with diffuse radio emission, and longer-lived or narrow jets successfully escaping the cluster core to produce cocoons with radio hotspots.