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Title: Probing the evolution of the most massive galaxies
Author: Buchan, Stewart William
ISNI:       0000 0004 7960 7357
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2018
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This thesis sets more stringent constraints on how the most massive (log Mstar ≥ 11.5[MΘ]) local, central galaxies have assembled their stellar mass, especially the relative roles of in-situ growth versus later accretion via mergers. To achieve this, I developed a series of semi-empirical/phenomenological models which, by construction, have few theoretical assumptions or free parameters. I firstly show that by comparing basic abundance matching predictions to observations of massive galaxies, the high-mass slope of the Mstar-Mhalo relation appears to be substantially steeper than the commonly used relations in the literature, and the scatter is small (∼ 0.15 dex). With the aid of the semi-empirical model I developed, which is based around this steeper abundance matching relation, I find that massive galaxies can grow by a factor two in stellar mass between z = 1 and z = 0 and a factor of four in size over the same redshift range, providing that mergers are efficient. Next, I populate a catalogue of massive dark matter haloes with galaxies through the above abundance matching relations, and compare the average stellar mass to total baryonic mass of their progenitors at their putative formation epoch, zform= 2 − 4. I find that the former is in fact equal to, if not greater than the latter. This would imply that if galaxies form in a strict monolithic collapse, the efficiency of converting baryons into stars needs to be extremely high, if not 100%. I also argue that this means they would need to be born extended, which may provide an observational test to discern between early versus late formation scenarios. I then outlined a promising framework to set constraints on the evolution of the slope and scatter of the high-mass end of the Mstar-Mhalo relation in a way designed to bypass observational systematics. I utilised the halo mass distribution of massive central and satellite galaxies at z = 0.5. The former is used to constrain the relation at z = 0.5 and the latter at their redshift of infall: 0.5 < z ≤ 1.2. By comparing the two relations, I find signs that individual massive galaxies have some stellar mass growth over this epoch. Finally, I show the results of two complementary projects involving numerical simulations that are designed to enhance and check the results presented in the above works. Using novel semi-empirical/phenomenological models, this thesis indicates that massive, central galaxies assemble a substantial amount of their stellar mass at later epochs ratherthan forming through extremely efficient star-bursts at high redshift.
Supervisor: Shankar, Francesco Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available