Interaction of Hydra A Jets with the Intracluster Medium

Abstract

The physics of jets from Active Galactic Nuclei (AGN) and their interaction with the interstellar medium (ISM) and intracluster medium (ICM) is an important research area of modern astronomy. Over the last few decades theoreticians have studied AGN jets both analytically and numerically. However, to date, a complete understanding on the jet energetics and composition, jet velocity, complex jet morphology and jet-ICM interaction is lacking. This thesis aims to understand the energetics and composition of the jet near its origin, its interaction with the galaxy and cluster, focussing on detailed models of the inner structure of the Hydra A radio source. Analysing radio observations of the inner lobes of Hydra A by Taylor et al. (1990), I confirm jet power estimates 1045 ergs s􀀀1 derived byWise et al. (2007) from dynamical analysis of the X-ray cavities. With this result and a model for the galaxy atmosphere, I explore the jet-ICM interactions occurring on a scale of 20 kpc using relativistic hydrodynamic simulations. The key features of my modelling are that i) I identify the four bright knots in the northern jet at approximately 4, 7, 11 and 16 kpc (deprojected) from the radio core as biconical reconfinement shocks, which result when an over pressured jet starts to come into equilibrium with the galactic atmosphere ii) the curved morphology of the source and the turbulent transition of the jet to a plume are produced by the dynamical interaction of a precessing jet with the ICM. I study the inner 10 kpc of the northern jet utilising two dimensional axisymmetric simulations. Through an extensive parameter space study I deduce that the jet velocity is approximately 0:8 c at a distance 0:5 kpc from the black hole. The combined constraints of jet power, the observed jet radius profile along the jet, and the estimated jet pressure and jet velocity imply a value of the jet density parameter 13 for the northern jet. To study the complex source morphology within 20 kpc (on the northern side) I generalise my axisymmetric model to a three dimensional jet-ICM interaction model incorporating jet precession. Utilising the jet parameters obtained from the best fit axisymmetric model, a range of precession periods and two values of the precession angle I produce a set of 3D models. With the precessing jet model I successfully reproduce key features of the inner 20 kpc of the Hydra A northern jet: i) Four bright knots along the jet trajectory at approximately correct locations ii) The curvature of the jet within 10 kpc iii) Turbulent transition of the jet to a plume iv) A misaligned bright knot in the turbulent flaring zone. The best matching model for the Hydra A northern jet gives a precession period 1 Myr and a precession angle 20 . A low Mach number 1:85 of the forward shock indicates a gentle heating of the ICM by the source in its early stages. Show more