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No description available.

No description available.

No description available.

No description available.

No description available.

We incorporate a model for black hole growth during galaxy mergers into the semi-analytical galaxy formation model based on ACDM proposed by Baugh et al. (2005). Our black hole model has one free parameter, which we set by matching the observed zeropoint of the local correlation between black hole mass and bulge luminosity. We present predictions for the evolution with redshift of the relationships between black hole mass and bulge properties. Our simulations reproduce the evolution of the optical luminosity function of quasars. We study the demographics of the black hole population and address the issue of how black holes acquire their mass. We find that the direct accretion of cold gas during starbursts is an important growth mechanism for lower mass black holes and at high redshift. The reassembly of pre-existing black hole mass into larger units via merging dominates the growth of more massive black holes at low redshift. As redshift decreases, progressively less massive black holes have the highest fractional growth rates, in line with recent claims of 'downsizing’ in quasar activity. We are able to reproduce the observed population of rare, highly luminous quasars at z ~ 6 in the ACDM model, although we struggle when the model parameters are refined to those in the current best fit of Sanchez et al. (2006). which has been hinted at by recent observations. We find that the most massive black holes and the most luminous quasars at z ~ 6 are not hosted exclusively by the most massive dark matter haloes, as is often assumed. Finally, we repeat our study of the assembly histories of black holes using the new galaxy and black hole formation model of Bower et al. (2006), which includes AGN feedback. Black hole growth in this model is dominated by the accretion required to fuel AGN feedback at low redshifts and by the accretion during starbursts triggered by disc instabilities at high redshifts. At no redshift is growth by BH-BH mergers dominant, although we still predict a high BH-BH merger rate. The Bower et al. model gives a somewhat better match to the M(_BH) - bulge relations, while the Baugh et al. model gives a better match to the quasar luminosity function. We suggest future directions to explore with these models.

The main driver of the work in this thesis is the idea of chaotic accretion in galaxy centres. Most research in this area focuses on orderly or coherent accretion where supermassive black holes or supermassive black hole binaries are fed with gas always possessing the same sense of angular momentum. If instead gas flows in galaxies are chaotic, feeding occurs through randomly oriented depositions of gas. Previous works show that this chaotic mode of feeding can explain some astrophysical phenomena, such as the lack of correlation between host galaxy structure and the direction of jets. It has also been shown that by keeping the black hole spin low this feeding mechanism can grow supermassive black holes from stellar mass seeds. In this thesis I show that it also alleviates the ‘final parsec problem’ by facilitating the merger of two supermassive black holes, and the growth of supermassive black holes through rapid accretion. I also develop the intriguing possibility of breaking a warped disc into two or more distinct planes.

Supermassive black holes (SMBHs) have been gradually recognised as important elements of galaxy and cosmic structure evolution. Their connection with the large-scale environment is maintained via feedback processes – communication of a fraction of the accretion luminosity to the host galaxy. Feedback is conjectured to expel gas from galaxies, quench star formation and establish the observed correlations between SMBH mass and host galaxy properties. Efficient feedback requires rapid gas accretion and is therefore usually investigated within the context of quasar activity phases in SMBH evolution. In this Thesis, I investigate several implications of an SMBH wind feedback model, advancing our understanding of feedback processes and the immediate environment of SMBHs. I consider analytically the large-scale outflows and their observable properties. I find that rapidly accreting SMBHs may sweep galaxies clear of gas, turning them into red-and-dead spheroids. I apply the same feedback model to our Galaxy. Its SMBH, Sgr A∗, is currently exceptionally quiescent, although it must have been more active in the past in order to have grown to its present size. I investigate, both analytically and numerically, a short burst of activity which may have occurred ∼ 6 million years ago, producing an outflow which formed two large γ-ray emitting bubbles perpendicular to the Galactic plane. The results show that dynamical footprints of outflows may persist for a long time and provide evidence of past AGN activity in quiescent galaxies. I also present a model for the short-timescale flares observed daily in Sgr A∗, based on tidal disruption and evaporation of asteroids in the vicinity of the SMBH. The model explains some observed flare properties, and thus improves our understanding of the processes occurring close to the SMBH. It also provides predictions for observable effects as the quiescent luminosity of Sgr A∗ varies on long timescales.

We present a study into the existence of the broad Fe Ka line, the hot nature of the ionised gas surrounding Active Galactic Nuclei, most commonly referred to as 'warm absorbers', and the AGN environment. We begin with an investigation of the Seyfert 1.5 galaxy NGC 3516. In our analysis, we use the Chandra telescope to explore the environment around the black hole, utilising the high resolution of the spectrometer to constrain the physical parameters. In conjunction with this we use the large effective area of Suzaku in order to detect subtle features such as the broad KO' feature. In this work we come to the conclusion that the effects of partial covering are insufficient to explain the existence of a broad Fe Ka feature. Interestingly enough however, they are required in order to provide an understanding of the soft X-ray region; although other models may provide an adequate explanation without the requirement for invoking partial covering. We go 011 to perform an analysis of 18 different Seyfert galaxies observed with the Chandra HETG, using an in-house pipeline. The purpose of the pipeline is to enable the automised fitting of phenomenological models to AGN, to aid with the diagnosis and study of warm absorbers. From this, we have determined that Seyfert 1 galaxies have negligible effect on the hard X-ray band, and that no correlation exists between the other Seyfert classifications and possible effects on the hard X-ray. We further identify a number of emission lines features throughout these AGN. Finally we investigate numerous possible relationships among the parameters of the warm absorbers in an attempt to understand the mechanism by which they are created. While this is inconclusive, we demonstrate that the mass ejection rate of the warm absorbers is low in comparison to the mass accretion rate and bolometric luminosity of the sources.