Simulating the growth of a disk galaxy and its supermassive black hole in a cosmological context.

Supermassive black holes (SMBHs) are ubiquitous in the centers of galaxies. Their formation and subsequent evolution is inextricably linked to that of their host galaxies, and the study of galaxy formation is incomplete without the inclusion of SMBHs. The present work seeks to understand the growth and evolution of SMBHs through their interaction with the host galaxy and its environment. In the first part of the thesis (Chap. 2 and 3), we combine a simple semi-analytic model of outflows from active galactic nuclei (AGN) with a simulated dark matter density distribution to study the impact of SMBH feedback on cosmological scales. We find that constraints can be placed on the kinetic efficiency of such feedback using observations of the filling fraction of the Ly[alpha] forest. We also find that AGN feedback is energetic enough to redistribute baryons over cosmological distances, having potentially significant effects on the interpretation of cosmological data which are sensitive to the total matter density distribution (e.g. weak lensing). However, truly assessing the impact of AGN feedback in the universe necessitates large-dynamic range simulations with extensive treatment of baryonic physics to first model the fueling of SMBHs. In the second part of the thesis (Chap. 4-6) we use a hydrodynamic adaptive mesh refinement simulation to follow the growth and evolution of a typical disk galaxy hosting a SMBH, in a cosmological context. The simulation covers a dynamical range of 10 million allowing us to study the transport of matter and angular momentum from super-galactic scales all the way down to the outer edge of the accretion disk around the SMBH. Focusing our attention on the central few hundred parsecs of the galaxy, we find the presence of a cold, self-gravitating, molecular gas disk which is globally unstable. The global instabilities drive super-sonic turbulence, which maintains local stability and allows gas to fuel a SMBH without first fragmenting completely into stars. The fueling appears to be a stochastic process, with no preferred timescale for accretion over the duration of the simulation.

Supermassive black holes are now believed to play an important role in the evolution of the Universe. Every respectable galaxy hosts in its center a black hole that appears to regulate the growth of the galaxy itself. In this book, leading experts in the field review the most recent theoretical and observational results on the following topics: - formation and growth of the first black holes in the Universe and their role in the formation and evolution of galaxies - the physics of black-hole accretion and the production of relativistic jets - binary black-hole mergers and gravitational radiation. Theoretical work is supplemented by the most recent exciting results from space and ground based observatories. This volume is useful research and reference tool for the entire astrophysical community.

The ultimate proofs that black holes exist have been obtained very recently thanks to the detection of gravitational waves from their coalescence and due to material orbiting at a distance of some gravitational radii imaged by optical interferometry or X-ray reverberation mapping. This book provides three comprehensive and up-to-date reviews covering the gravitational wave breakthrough, our understanding of accretion and feedback in supermassive black holes and the relevance of black holes for the Universe since the Big Bang. Neil J. Cornish presents gravitational wave emission from black hole mergers and the physics of detection. Andrew King reviews the physics of accretion on to supermassive black holes and their feedback on host galaxies. Tiziana Di Matteo addresses our understanding of black hole formation at cosmic dawn, the emergence of the first quasars, black hole merging and structure formation. The topics covered by the 48th Saas-Fee Course provide a broad overview of the importance of black holes in modern astrophysics.

Supermassive black holes are now believed to play an important role in the evolution of the Universe. Every respectable galaxy hosts in its center a black hole that appears to regulate the growth of the galaxy itself. In this book, leading experts in the field review the most recent theoretical and observational results on the following topics: - formation and growth of the first black holes in the Universe and their role in the formation and evolution of galaxies - the physics of black-hole accretion and the production of relativistic jets - binary black-hole mergers and gravitational radiation. Theoretical work is supplemented by the most recent exciting results from space and ground based observatories. This volume is useful research and reference tool for the entire astrophysical community.

While mounting observational evidence suggests the coevolution of galaxies and their embedded massive black holes (MBHs), a comprehensive astrophysical understanding which incorporates both galaxies and MBHs has been missing. To tackle the nonlinear processes of galaxy formation, we develop a state-of-the-art numerical framework which self-consistently models the interplay between galactic components: dark matter, gas, stars, and MBHs. Utilizing this physically motivated tool, we present an investigation of a massive star-forming galaxy hosting a slowly growing MBH in a cosmological LCDM simulation. The MBH feedback heats the surrounding gas and locally suppresses star formation in the galactic inner core. In simulations of merging galaxies, the high-resolution adaptive mesh allows us to observe widespread starbursts via shock-induced star formation, and the interplay between the galaxies and their embedding medium. Fast growing MBHs in merging galaxies drive more frequent and powerful jets creating sizable bubbles at the galactic centers. We conclude that the interaction between the interstellar gas, stars and MBHs is critical in understanding the star formation history, black hole accretion history, and cosmological evolution of galaxies. Expanding upon our extensive experience in galactic simulations, we are well poised to apply this tool to other challenging, yet highly rewarding tasks in contemporary astrophysics, such as high-redshift quasar formation.

I use cosmological hydrodynamic simulations to investigate different aspects of the evolution of galaxies and massive black holes across cosmic time. First, I present high resolution "zoom-in" simulations including various prescriptions for galactic outflows designed to explore the impact of star-formation driven winds on the morphological, dynamical, and structural properties of individual galaxies from early times down to z = 2. Simulations without winds produce massive, compact galaxies with low gas fractions, super-solar metallicities, high bulge fractions, and much of the star formation concentrated within the inner kpc. I show that strong winds are required to suppress early star formation, maintain high gas fractions, redistribute star-forming gas and metals over larger scales, and increase the velocity dispersion of simulated galaxies, more in agreement with the large, extended, turbulent disks typical of high-redshift star-forming galaxies. Next, I combine cosmological simulations with analytic models of black hole growth to investigate the physical mechanisms driving the observed connection between massive black holes and their host galaxies. I describe a plausible model consistent with available observations in which black hole growth is limited by galaxy-scale torques. In this torque-limited growth scenario, black holes and host galaxies evolve on average toward the observed scaling relations, regardless of the initial conditions, and with no need for mass averaging through mergers or additional self-regulation processes. Outflows from the accretion disk play a key role by providing significant mass loss, but there is no need for strong interaction with the inflowing gas in order to regulate black holes in a non-linear feedback loop. I discuss some of the main implications of this scenario in the context of current observations, including the distribution and evolution of Eddington ratios, the connection between major galaxy mergers, star formation, and nuclear activity, and the rapid growth of the first black holes in the early universe. Finally, I present preliminary results from simulations including a fully consistent treatment of black hole accretion and feedback indicating that the effects of powerful accretion-driven outflows on black hole growth itself may have a more limited impact than previously thought.