Simulating the jet-ISM interaction in GPS & CSS galaxies

Relativistic jets from AGNs are an important driver of feedback in galaxies. Interaction of such jets with an inhomogeneous ISM significantly affect the evolution of the galaxy. A class of galaxies where such interactions are thought to be occurring are the Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) galaxies. Such galaxies are characterised by a distinct turnover in the radio spectrum, which is often attributed to free-free absorption from a turbulent ISM surrounding the jet. I shall present the results of our recent 3D relativistic hydrodynamic simulations probing the interaction of such AGN jets with a turbulent ISM. We find that the jet couples strongly with the ISM launching fast lateral outflows of shocked ionised gas. The increased turbulence and densities in the immediate vicinity of the jet result in sharp turnover in the simulated radio spectrum, corresponding to the GPS phase of the galaxy's evolution, eventually becoming a CSS type. Our simulations show that relativistic jets can be an important driver of "AGN feedback" affecting the ISM over scales of several kilo-parsecs during the early phase of its evolution. Such interactions are expected to have unique observational signatures which can be verified with observational studies. I will discuss the implication of our results for the evolutionary history of galaxies, how they correlate with previously observed results and more recent observational results of jet-ISM interaction in some galaxies, which were carried out prompted by the theoretical simulations.