Author: Ilian Tzankov Iliev
Publisher:
ISBN:
Category : Galaxies
Languages : en
Pages : 576

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Author: Michael Travis Busha
Publisher:
ISBN:
Category :
Languages : en
Pages : 378

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Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 1044

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Author: Matthew William Craig
Publisher:
ISBN:
Category :
Languages : en
Pages : 314

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Book Description

Author: Alexandre Barreira
Publisher: Springer
ISBN: 3319336967
Category : Science
Languages : en
Pages : 234

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Book Description
This unique thesis covers all aspects of theories of gravity beyond Einstein’s General Relativity, from setting up the equations that describe the evolution of perturbations, to determining the best-fitting parameters using constraints like the microwave background radiation, and ultimately to the later stages of structure formation using state-of-the-art N-body simulations and comparing them to observations of galaxies, clusters and other large-scale structures. This truly ground-breaking work puts the study of modified gravity models on the same footing as the standard model of cosmology. Since the discovery of the accelerating expansion of the Universe, marked by the awarding of the 2011 Nobel Prize in Physics, there has been a growing interest in understanding what drives that acceleration. One possible explanation lies in theories of gravity beyond Einstein’s General Relativity. This thesis addresses all aspects of the problem, an approach that is crucial to avoiding potentially catastrophic biases in the interpretation of upcoming observational missions.

Author: Camila Anahi Correa
Publisher:
ISBN:
Category : Cosmology
Languages : en
Pages : 203

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Book Description
The goal of this thesis is to (i) explore the physics that drives universal accretion history of dark matter halos; (ii) determine the relation between the halos accretion history and the halos internal structure; and (iii) disentangle the impact of halos accretion history on galaxy evolution. To address these topics, we first use the extended Press-Schechter (EPS) formalism to derive the halo mass accretion history (MAH) from the growth rate of initial density perturbations. We show that the halo MAH can be well described by an exponential function of redshift in the high-redshift regime. However, in the low-redshift regime the mass history growth slows down because the growth of density perturbations is halted in the dark energy dominated era due to the accelerated expansion of the Universe. As a result, in the low-redshift regime the halo MAH can be described by a power-law function of redshift. We complement this study with the analysis of MAHs of dark matter halos using a suite of cosmological simulations. We explore the relation between the density profile of dark matter halos and their MAHs, and confirm that the formation time, defined as the time when the virial mass of the main progenitor equals the mass enclosed within the scale radius, correlates strongly with concentration. We combine both analysis, analytic and numerical, to show that the halo MAH is the link between halo concentration and the initial density perturbation field. The connection found between the halo MAH and its density profile reached in these studies was vital to derive a semi-analytic, physically motivated model for dark matter halo concentration as a function of halo mass and redshift. Because the semi-analytic model is based on EPS theory, it can be applied to wide ranges in mass, redshift and cosmology. The resulting concentration-mass (c-M) relations are found to agree with the simulations, and because the model applies only to relaxed halos, they do not exhibit the upturn at high masses or high redshifts found by some recent works. We predict a change of slope in the z~0 c-M relation at a mass scale of 10^11 solar masses. We find that this is due to the change in the functional form of the halo MAH, which goes from being dominated by an exponential (for high-mass halos) to a power-law (for low-mass halos). During the latter phase, the core radius remains approximately constant, and the concentration grows due to the drop of the background density. We then connect the evolution of dark matter halos to the evolution of galaxies. We investigate the hot hydrostatic halo formation and its dependence on feedback mechanisms. We find that in the presence of energy sources like stellar feedback, the hot halo mass increases and the mass scale of hot halo formation is reduced. Active galactic nuclei (AGN) do not affect the hot halo as strongly. We develop a semi-analytic approach that makes use of both, the hot halo mass and the fraction of shock-heated gas, to calculate a `critical mass scale' for hot halo formation. We find that this mass scale, where the heating rate produced by accretion shocks equals cooling, is the point in mass above which halos develop a stable hot atmosphere. In the redshift range z=0-4, the critical mass is 10^11.7 solar masses, but it then increases for increasing redshift, in very good agreement with our numerical results. Finally, we investigate the physics that drives the gas accretion rate onto galaxies at the center of dark matter halos. We separately analyze the gas accretion rate onto the interstellar medium (ISM) and onto the galaxy. We find that the accretion rate onto the ISM remains roughly constant in halos larger than 10^11.7 solar masses, whereas the accretion rate onto the galaxy increases with increasing halo mass and flattens in the halo mass range 10^11.7-10^12.7 solar masses, and at redshifts z

Author: Andre Balogh
Publisher: Springer
ISBN: 149393547X
Category : Science
Languages : en
Pages : 357

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Book Description
This book offers eleven coordinated reviews on multi-scale structure formation in cosmic plasmas in the Universe. Observations and theories of plasma structures are presented in all relevant astrophysical contexts, from the Earth’s magnetosphere through heliospheric and galactic scales to clusters of galaxies and the large scale structure of the Universe. Basic processes in cosmic plasmas starting from electric currents and the helicity concept governing the dynamics of magnetic structures in planet magnetospheres, stellar winds, and relativistic plasma outflows like pulsar wind nebulae and Active Galactic Nuclei jets are covered. The multi-wavelength view from the radio to gamma-rays with modern high resolution telescopes discussed in the book reveals a beautiful and highly informative picture of both coherent and chaotic plasma structures tightly connected by strong mutual influence. The authors are all leading scientists in their fields, making this book an authoritative, up‐to‐date and enduring contribution to astrophysics.

Author: International Astronomical Union. Symposium
Publisher: Cambridge University Press
ISBN: 9780521889858
Category : Science
Languages : en
Pages : 542

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Book Description
The paradigm of a dark energy- and dark matter-dominated Universe, with the hierarchical merger scenario for the formation of galaxies, has scored impressive successes in matching the observed Universe. However, the theory fails to explain the difficulty in generating ordinary disk galaxies such as the Milky Way, suggesting that some important physics must be missing in current models. IAU Symposium 254 was organized to address this question, gathering researchers from an unusually broad range of fields, from cosmology to interstellar matter, and the formation and evolution of stars. High-class reviews, lectures and posters combine to define the frontiers in the field and point the way to new avenues of research. This volume presents a unique set of succinct overviews illuminating the full range of topics in this very active field. It also honors Danish astrophysicist Bengt Strömgren (1908-1987), who laid much of the foundation for this entire field.

Author: Kyungjin Ahn
Publisher:
ISBN:
Category : Dark matter (Astronomy)
Languages : en
Pages :

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Author: Laura G. Book
Publisher:
ISBN:
Category : Celestial mechanics
Languages : en
Pages : 266

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