Feeding the AGN with backflows

TL;DR

This paper models and simulates the internal backflows within AGN jet cocoons, revealing how density and entropy gradients drive inflows that match theoretical predictions across various AGN parameters.

Contribution

It develops a new model for AGN cocoon backflows and validates it with extensive 2D simulations, linking flow dynamics to jet power and black hole mass.

Findings

Flow gradients cause significant backflows near hot spots.

Predicted mass inflows agree with simulation results.

Simple streamline solutions effectively describe the flow patterns.

Abstract

We study the internal circulation within the cocoon carved out by a relativistic jet emanating from an AGN, first developing model and then validating it using a series of numerical simulations. We notice that a significant increase of in this flow arises because gradients in the density and entropy develop near the hot spot, as a consequence of Crocco vorticity theorem. We find simple solutions for the streamlines, and we use them to predict the mass inflow rates towards the central regions. The 2D simulations we perform span a rather wide range of mechanical jet's input power and Black Hole masses, and we show that the predicted nuclear mass inflows are in good agreement with the theoretical model.