Project Details
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The impact of AGN-radiation on the evolution of galaxies and their circumgalactic medium

Applicant Dr. Aura Obreja
Subject Area Astrophysics and Astronomy
Term from 2020 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 443044596
 
Final Report Year 2024

Final Report Abstract

Active galactic nuclei (AGNs) are powerful sources of radiation that can modify the structure of the gas phase around galaxies over large distances. In simulations, their effects are typically modelled as either thermal energy and/or momentum transfer to the surrounding gas, giving rise to so-called thermal and/or kinetic AGN feedback. Massive galaxies simulated without AGN feedback end up with too many stars for their dynamical mass at low redshifts, which is inconsistent with observations. While these implementations lead to similar statistical properties of galaxies, they lead to different properties of the Circumgalactic Medium (CGM), a difficult-to-measure multi-phase gas component that permeates the dark matter halo regions around galaxies. This project has shown that taking into account the direct photoionisation effect of AGNs on the gas, also known as AGN electromagnetic feedback, can halt the catastrophic cooling of the CGM in simulated quasar host halos, with the fraction of gas removed from this phase being a strong function of the ionisation cone opening angle. Furthermore, the CGM line emission and the covering fraction of optically thick absorbers in high redshift simulations can be brought into agreement with observations for specific combinations of supermassive black hole mass, accretion rate, and ionisation cone opening angle. AGN electromagnetic feedback provides a more natural way of coupling the supermassive black holes to their environment in simulations than the widely used isotropic thermal feedback. Importantly, this project provided the proof of concept of how CGM observations can be used to infer properties of the central AGN engine. This project also made a significant contribution to the goal of measuring CGM budgets in quasar host galaxies at high redshift, and linking the CGM emission line Lya nebulae sometimes observed around quasars to the larger Mpc scale environment of massive galaxies. In particular, we found that the orientations of the Lya emission nebulae on tens of kpc scales lie roughly along the projected long axis of their surrounding galaxy distributions on Mpc scales, as traced with submillimeter observations.

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