Browsing Doctoral Dissertations by Author "Smole, Majda"
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Smole, Majda (Beograd , 2017)[more][less]
Abstract: Formation mechanism of supermassive black holes (SMBHs) observed in the early Universe is still not fully understood. The goal of this thesis is to nd under what conditions black hole (BH) remnants of Population III stars can form SMBH with mass 109 M by redshift z = 7. We use Millennium and Millennium-II N-body cosmological simulations to investigate BH growth on cosmological scales. In order to exploit both high mass resolution in the Millennium-II simulation and large box size in the Millennium simulation, we develop a method to combine these two simulations together. BHs can grow through mergers with other BHs and through episodes of gas accretion triggered by major mergers of dark matter haloes. As a constraint in our model, we use observed BH mass function at redshift z = 6. We nd that BH seeds with masses 100 M could grow to SMBHs in distant quasars if e ective Eddington ratio is xed at fEdd = 3:7 and each accretion episode is limited to 50 Myr. During a BH merger asymmetric emission of gravitational radiation can lead to BH kick. Gravitational wave recoil can completely eject BH from it's host if the kick velocity is larger than the escape velocity from the galaxy. Since gravitational wave recoil could a ect SMBH growth through mergers, recoiling BHs are investigated in di erent models of host galaxies. BH trajectories are investigated in static and evolving dark matter halo potential described by NFW and Einasto density distributions. We nd that evolution of dark matter haloes clearly impact their capability to retain recoiling BHs since escape velocities are lower for smaller haloes at high redshifts. If the Einasto pro le is considered, then a larger number of complete BHs ejections is expected compared to NFW potential. Further, we construct analytical and numerical host galaxy models whose components are dark matter halo, bulge and disc. If baryonic component of a galaxy is included escape velocity is higher compared to a purely dark matter halo potential. Major (1:1) and minor (1:10) galaxy remnants are modeled separately. In numerical models BHs are ejected from their host centre before galaxy merger is completed, so escape velocities are generally lower in numerical models compared to analytical models where galaxy potential is unperturbed. Even though BHs could occasionally escape the most massive hosts, our model is not considerably sensitive to the gravitational wave recoil except for mergers of equal mass BHs in the least massive haloes at high redshifts where kick velocities of Vk . 100 km=s could permanently eject BHs from their hosts. URI: http://hdl.handle.net/123456789/4502 Files in this item: 1
Majda_Smole_disertacija.pdf ( 4.149Mb )
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