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Monsters in the Deep: Using simulations to understand the excess baryonic mass in the centres of high-mass, early-type galaxies

  • C.R. Barber
20 november 2018
Rapenburg 73
2311 GJ Leiden


This thesis aims to enhance the understanding of galaxies by testing theoretical models of galaxy formation against observations, particularly in the cases of extreme systems. To this end we performed state-of-the-art cosmological, hydrodynamical simulations of a model universe which has been calibrated such that the numbers and sizes of galaxies agree with our own Universe. We found that the model naturally produces some galaxies with "monstrous" central supermassive black holes similar to those recently found observationally, which form due to early formation times and the loss of stars via tidal forces exerted by more massive galaxies, giving us clues about how such systems may form in the real Universe.

Some massive elliptical galaxies have been found to have larger than expected stellar mass in their central regions given their luminosity, implying that the distribution of masses of stars at birth (the stellar initial mass function, or IMF) may be different than expected in such systems. To test the consequences of these findings we performed new simulations with a modified IMF calibrated to reproduce the excess mass in these galaxies. We test two models, in which the mass in enhanced either by increasing the fraction of (dim, long-lived) dwarf stars or the fraction of high-mass (short-lived) stars that leave behind (invisible) black holes. We find that such models are able to produce realistic galaxy populations, but that assumptions made about the functional form of the IMF variations can have important consequences for the predictions of galaxy formation models.


  • Prof.dr. J. Schaye


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