Speaker
Description
We present predictions for the non-thermal pressure (NTP) induced in galaxy clusters undergoing energetic jet outbursts from an active galactic nucleus (AGN). Our model simulates a population of jets from power-law distributions in their power and age, which are analytically modelled as they propagate through the intracluster medium. We model the energy coupling between the jet and the surrounding gas as a function of cluster radius based on thermodynamic arguments, inferring the fraction of input energy dissipated as bulk fluid motion. This allows us to compute the fraction of NTP to total pressure, $\mathcal{F}\equiv p_\mathrm{nt}/p$, induced in the system as kinetic feedback. For this jet population, we predict the mean profile of the NTP fraction in the cluster’s core, for a range of cluster environments and AGN duty cycles, $\delta\equiv t_\mathrm{on}/(t_\mathrm{on}+t_\mathrm{off})$. In the cluster environments considered, we find that the NTP fraction is $\left<\mathcal{F}\right>\lesssim8\%$ when $\delta=0.1$; $\left<\mathcal{F}\right>\lesssim11\%$ when $\delta=0.2$; and $\left<\mathcal{F}\right>\lesssim12\%$ when $\delta=0.3$. These predictions are in good agreement with observational constraints, suggesting that AGN feedback imparts only small non-thermal contributions to the cores of galaxy clusters. Furthermore, we find a relationship between the peak of the mean NTP fraction and the AGN duty cycle, in a range of cluster environments, which is driven by a $\sqrt{\delta}$ dependence. Using this relationship, we predict the value of Perseus’ AGN duty cycle by using the Hitomi observations of Perseus’ central NTP fraction. This gives us a median AGN duty cycle of $\delta\simeq0.27$, which is in excellent agreement with observational evidence of Perseus' AGN activity over the past few outbursts. We plan to investigate this relationship between a cluster’s central NTP and its AGN activity further by utilising state-of-the-art numerical simulations. This will allow us to determine the feasibility of inferring the AGN activity of real clusters from their central NTP fraction, such as those currently being observed by XRISM.
