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AGN feedback from Mpc to pc scale: radio-mode, quasar-mode and backflows

Dr. Salvatore Cielo

October 18th, 2017


Mechanical feedback by jets from Active Galactic Nucei (AGN) is a key process in galaxies and galaxy clusters: the energy input from the jets (in literature often addressed as radio-mode feedback) is crucial in determining the properties of the hot gas (especially in cool-core galaxy clusters), as well as inflating the large cavities we observe in the X-ray gas. The interaction of AGN outflows (both jets and radiation) with cold gas in galactic environment  (quasar-mode feedback) can instead impact the cosmic star formation rate, as well as power galaxy-wide atomic and molecular outflows. Finally, AGN can affect its own proximity, regulating central gas accretion and giving rise to (sometimes) self-sustained feeding/feedback cycles.

I will follow the interaction of AGN with intergalactic and interstellar gas from large to small scales (radio-mode) with the use of numerical simulations. As radio-mode feedback, I will discuss the properties and the energetics​ of the hot gas bubbles inflated by multiple jet events in a galaxy ​cluster, with the aid of synthetic but realistic X-ray observations. On galactic scales, I will discuss the mechanical coupling of jets and radiation with a clumpy galactic disc, show how AGN can trigger dense and fast outflows, and briefly describe the impact on galactic star formation.

I will finally discuss "backflows" --- i.e. galaxy-wide gas circulation patterns that "flow back" to the circum-nuclear region --- as a mechanism for AGN self-regulation. I will show, complementing the simulations with a small-scale analytical model, how backflows are able to convey large amounts of cold gas to the central region, that can boost the AGN power by even a factor of ten.