The impact of active galactic nuclei and cooling mechanisms on the intra-cluster properties in the L-Galaxies semi-analytical model

Fournier, Benoit (2019) The impact of active galactic nuclei and cooling mechanisms on the intra-cluster properties in the L-Galaxies semi-analytical model. Doctoral thesis (PhD), University of Sussex.

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The intra-cluster medium (ICM) plays a key role in galaxy formation. The cooling of hot gas and its recycling due to feedback are key parameters in understanding the regulation of star formation. Semi-analytical models (SAMs) are quick simulations that allow us to test our understanding of galaxy formation processes. Most of them produce results agreeing fairly well with various galaxy observations, however they fail in reproducing the ICM properties.
In this work we focus on the active galactic nuclei (AGN) feedback and cooling mechanisms affecting the ICM, by developing new physically motivated methods that give a more accurate ICM description in the L-Galaxies SAM. We start by correcting the baryon content of each halos in the simulation. Due to halo mass fluctuations, halos ended up with an over density of baryons. This problem was resolved by introducing an extra phase for the baryons to keep track of the gas that would be considered leaving the halo (during contractions) or inflating (halo growth).
Although this solution solved the baryon problems, it did not answer the question of the excess of hot gas stored inside the virial radius. We investigated different feedback mechanisms, from SNR to black holes and found that ejecting the gas with powerful AGN jets is compulsory to reduce the hot gas content of the halos. In order to reduce the gas content, a new model of AGN feedback was implemented and tuned to reproduce the observational gas fractions available in the literature. The AGN can not only now reheat cold and cooling gas, but also eject it via powerful jets. In addition to this feedback, four new black hole accretion models were compared, based on different gas reservoir. The most accurate agreement with observations for most AGN and galaxy properties came from a model where the AGN was fed by accretion of cold clouds from the ISM of the host galaxy.
Finally we investigate the effect of our improved feedback on the ICM itself. In addition to the new AGN feedback, we developed a more physical cooling mechanism based on Bremsstrahlung radiation and a Beta profile of the gas. This change enabled us to give X-ray predictions for our model to compare with observational data, including the most recent XMM results. We found that the change in cooling only slightly affects the results (gas fractions, metallicities), as expected. However the X-ray luminosities of our groups and clusters of galaxies are now in agreement with observations, mainly due to the gas content reduction done by the new feedback mechanism.
This new version of L-Galaxies manages to reproduce both galaxies and ICM properties in fairly good agreement with observational data.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy > QB0495 Descriptive astronomy > QB0856 Galaxies
Depositing User: Library Cataloguing
Date Deposited: 12 Jul 2019 07:50
Last Modified: 12 Jul 2019 07:50

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