AGN Jet-induced Feedback in Galaxies. I. Suppression of Star Formation

Abstract

(Abridged) We study the interaction of relativistic jets from AGNs with the ISM in their host galaxy, using a series of Adaptive Mesh Refinement simulations of the evolution of the interaction between the cocoon produced by the jet with a dense cloud, placed very near the cocoon's path. We vary only the jet's input power between P_{jet} = 10^{41}-10^{47} {\rm erg/sec}. The density Probability Distribution Function (PDF) within the cocoon can be described in terms of two distinct components, which are also spatially distinct: a low- and a high-density component. The PDF of the post-shocked region is well approximated by a modified lognormal distribution, for all values of $P_{jet}$. During the active phase, when the jet is fed by the AGN, the cloud is subject both to compression and stripping, which tend to increase its density and diminish its total mass. When the jet is switched off (i.e. during the passive phase) the shocked cloud cools further and tends to become more filamentary, under the action of a back-flow which develops within the cocoon. We study the evolution of the star formation rate within the cloud, assuming that is determined by a Schmidt-Kennicutt law, and we analyze the different physical factors which have an impact on the star formation rate. We show that, although the star formation rate can occasionally increase, on time scales of the order of $10^{5}-10^{6}$ yrs, star formation will be inhibited and the cloud fragments. The cooling time of the environment within which the cloud is embedded is however very long: thus, star formation from the fragmented cloud remains strongly inhibited.