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Title: Black holes in the formation and evolution of galaxies
Author: Cattaneo, A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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As a result of this research, it is now accepted that quasars and galaxies are not unrelated phenomena. Instead, there is now substantial evidence that most galaxies have passed through an active phase at an early evolutionary stage. In spite of this observational progress, the modelling of quasars is still in a preliminary state. In most of the articles published before the last year the luminosity function of quasars is computed by convolving the halo mass function with prescriptions to associate a light curve to a dark matter halo. This procedure has been useful in demonstrating that the activity of quasars can be related to structure formation through hierarchical clustering, but is inadequate to study the link between quasars and galaxy formation, because it does not contain any (realistic) treatment of cooling and star formation. Attempts at more detailed modelling have fallen into two categories depending on the mechanism postulated for fuelling quasars: quasars may accrete most of their mass from cold gas in major mergers (Cattaneo, Haehnelt and Rees 1999; Kauffmann and Haehnelt 2000; Cattaneo 2001a,b; and Haehnelt and Kauffmann 2001), or they may be fuelled with hot gas in cooling flows (Nulsen and Fabian 2000). This thesis is one of the first attempts to model quasars in Monte Carlo simulations of galaxy formation. The simulations begin with the construction of merger trees for a set of dark matter haloes representative of the universe at z = 0. Subsequently these trees are populated with galaxies and quasars. It is assumed that, whenever two galaxies of comparable mass merge, an elliptical forms, while a fraction of the gas in the discs of the merging galaxies goes into the formation or refuelling of a supermassive black hole according to a specified accretion law. My research find results that are in substantial agreement with those of Kauffman and Haehnelt: the consumption of gas by stars is the main reason for the decline of quasars at low redshift but that decline is insufficient without a decrease in the fraction of accreted mass; not all the accretion is optically visible; the merger scenario underpredicts counts of very bright objects (chapter 3). Kauffmann and Haehnelt have used a much more sophisticated code for simulating galaxy formation, which includes a model for the synthesis of stellar population, while I have made a more systematic study of how the accretion law affects the quasar luminosity function. Moreover, I have considered that quasars can be an additional source of feedback besides supernova explosions. I have then repeated the same analysis with GalICS (Hatton et al. 2002) a much more powerful software for simulating galaxy formation. GalICS uses merger trees extracted from N-body simulations and incorporates STARDUST (Devriendt, Guiderdoni and Sadat 1999), a routine for calculating stellar evolution, feedback and the reprocessing of light by dust. Calculations with GaIICS reconfirmed my previous results (with less need for radiatively inefficient accretion). Adding a quasar contribution to starbursts spectra can reproduce the broad variety in the observed spectral distribution of ULIRGs.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available