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Black Hole Feedback in New Regimes: Modelling Dwarf Galaxies with Active Galactic Nuclei


Type

Thesis

Change log

Authors

Koudmani, Sophie 

Abstract

Contrary to the standard lore, there is mounting observational evidence that feedback from active galactic nuclei (AGN) may also play a role at the low-mass end of the galaxy population. In this thesis, I explore that possibility employing both isolated and cosmological simulations of dwarf galaxies.

Firstly, I perform high-resolution simulations of isolated dwarf galaxies. In these simulations, the AGN has only a limited direct effect on star formation rates. There is, however, a significant effect on outflows, which are notably enhanced by the AGN to much higher temperatures and velocities. This indicates that AGN may play an indirect role in quenching dwarf galaxies by hindering cosmic gas inflows.

I further investigate this quenching scenario using the cosmological simulation suite FABLE. While in the local Universe the majority of AGN in dwarfs are much dimmer than the stellar component, for z ≥ 2 there is a significant population of AGN that outshine their hosts. These high-redshift overmassive black holes contribute to the quenching of dwarfs, whereas at late cosmic times supernova (SN) feedback is more efficient. However, the lack of high-luminosity X-ray AGN in FABLE at low redshifts highlights an interesting possibility that SN feedback could be too strong in FABLE's dwarfs, curtailing AGN growth and feedback.

To examine the interplay between SNe and AGN accretion in more detail, I run a series of cosmological zoom-in simulations. I find that AGN feedback in tandem with more realistic SN feedback can be a successful alternative quenching mechanism to strong SN feedback in dwarfs, provided that the AGN is able to enter the high-accretion regime for at least part of its history. However, the Bondi rate generally prevents low-mass black holes from accreting efficiently, even though sufficient amounts of gas are available in these dwarfs.

Finally, I present a more robust AGN accretion model based on a unified accretion disc, which combines the ADIOS flow and standard thin disc schemes. This model will allow for the self-consistent exploration of the high-accretion regime in dwarf galaxies and detailed modelling of multimessenger signatures, in preparation for the next-generation electromagnetic and gravitational-wave observatories.

Description

Date

2021-04-01

Advisors

Sijacki, Debora
Haehnelt, Martin

Keywords

Computational astrophysics, Galaxy formation and evolution, Dwarf galaxies, Astrophysical black holes, Accretion discs

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Sponsorship
STFC (1951902)
STFC Studentship 1951902