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Simulations Of Mass Accretion Onto Dark Matter Haloes And Angular Momentum Transfer To A Milky Way Disk At High Redshift
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Book Synopsis Simulations of Mass Accretion Onto Dark Matter Haloes and Angular Momentum Transfer to a Milky Way Disk at High Redshift by : Henry William Tillson
Download or read book Simulations of Mass Accretion Onto Dark Matter Haloes and Angular Momentum Transfer to a Milky Way Disk at High Redshift written by Henry William Tillson and published by . This book was released on 2012 with total page 380 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Simulations of Mass Accretion Onto Dark Matter Haloes and Angular Momentum Transfer to a Milky Way Disk at High Redshift by : Henry William Tillson
Download or read book Simulations of Mass Accretion Onto Dark Matter Haloes and Angular Momentum Transfer to a Milky Way Disk at High Redshift written by Henry William Tillson and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Cosmological Simulations of Galactic Disc Assembly by : Elisa House
Download or read book Cosmological Simulations of Galactic Disc Assembly written by Elisa House and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We address the issue of kinematic heating in disc galaxies by analysing a suite of cosmological Milky Way-type disc simulations run with different particle-and grid-based hydrodynamical codes and different resolution, and compare them with observations of the Milky Way. By studying the kinematics of disc stars in these simulations, we seek to determine whether or not the existence of a fragile thin disc is possible within a cosmological framework, where multiple mergers and interactions are the essence of galaxy formation. We study the velocity dispersion-age relation for disc stars at $z=0$ and find that four of the simulations, the stellar disc appears to undergo continual/secular heating. Two other simulations suggest a "saturation" in the heating profile for young stars in the disc. None of the simulations have thin discs as old as that of the Milky Way. We also analyse the kinematics of disc stars at the time of their birth, and find that in some simulations old stars are born cold within the disc and are subsequently heated, while other simulations possess old stellar populations, which are born relatively hot. The models which are in better agreement with observations of the Milky Way's stellar disc undergo significantly lower minor-merger/assembly activity after the last major merger. By running a set of isolated Milky Way-type simulations with different resolution and different density thresholds for star formation we conclude that, on top of the effects of mergers, there exists a ``floor'' in the dispersion that is related to the underlying treatment of the heating and cooling of the interstellar medium, and the low density threshold which such codes use for star formation. A persistent issue in simulations of disc galaxies is the formation of large spheroidal components, and disc galaxies with larger bulge to disc ratios than is observed. This problem is alleviated by supernova feedback. We found that by increasing the feedback in the simulations, we decrease the amount of stars that are accreted onto the main galaxy. The star formation is quenched more efficiently in low mass satellites when stronger feedback is implemented as well as in the main halo. These effects result in a disc galaxy, which has formed less stars overall, but more importantly, contains less accreted stars. As the strong stellar feedback quenches the star formation in the small building blocks, the metallicity of the accreted stars is lower than in the case where less feedback was used. In the context of hierarchical formation, mass assembly is expected to be scale free. Yet the properties of galaxies depend strongly on their mass. We examine how baryonic physics has different effects at different mass scales by analysing three cosmological simulations using the same initial conditions that are scaled to three different masses. Despite their identical dark matter merger history, we show that the simulated galaxies have significantly different stellar accretion histories. As we go down in mass, the lowest mass progenitors are unable to form stars, resulting in a low mass galaxy with less accreted stars. The overall chemical properties are also distinct at the different mass scales, as one might expect from the mass-metallicity relation of observed galaxies. We examine gradients of chemical abundances with radius and with height above the disc, and look for properties that are retained at different mass scales and properties which change, often dramatically. We analyse the kinematic and chemical properties of their accreted and in-situ populations. Again, trends can be found that persist at all mass scales, providing signatures of hierarchical structure formation. We find that accreted populations in the high mass simulation did not resemble any of the populations in the lower mass galaxies, showing that the chemical properties of proto-galaxies, which merge at high redshift to form massive galaxies, differ from the properties of low mass galaxies that survive at z=0. We probe further the signatures of hierarchical structure formation at smaller scales, in dwarf galaxies. We analysed the morphologies, kinematics and chemical properties of two simulated dwarf galaxies with different merger histories. We again analyse the accreted and in-situ populations. Observations of dwarf galaxies have found that they are comprised of multiple components. Our simulated dwarfs indicate that such populations may indeed be a manifestation of the hierarchical formation process in action in these lower mass galaxies. In one simulated dwarf, the in-situ stellar component forms a thin disc and a thick disc. We show that the thick disc in this simulation forms from in-situ stars that are born kinematically hot in the disc from early gas-rich mergers. The thin disc is formed quiescently from the later infall of gas. The accreted stars in the simulation were found to form an extended stellar halo. Chemical signatures of the three populations are also explored. The second dwarf we analysed has different galactic components, a result found to be due to the different merger history of this galaxy. The last major merger in this simulation occurs early on in the formation process between two proto-galaxies of similar mass. The result is a dwarf galaxy comprised of a disc formed of in-situ stars and a flattened rotating stellar halo formed of accreted stars. The angular momentum of the accreted and old in-insitu stars is obtained from the last major merger. We discuss the resemblance of this flattened rotating stellar halo to fast rotating flattened elliptical galaxies, and propose that such structures may explain some of the observed extra-galactic thick discs. These studies show that galactic properties emerge through the complex inter-play between hierarchical structure formation, star formation, and feedback from supernovae. Different modelling of these processes will alter the simulated galaxy's properties, and detailed comparisons with observations can then be made to determine the dominant processes responsible for different galactic properties. We remain optimistic that further improvement in modelling will allow deeper insights into the processes of galaxy formation and evolution.
Book Synopsis Galaxies at High Redshift by : I. Pérez-Fournon
Download or read book Galaxies at High Redshift written by I. Pérez-Fournon and published by Cambridge University Press. This book was released on 2003-03-20 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume presents lectures of the XI Canary Islands Winter School of Astrophysics written by experts in the field.
Book Synopsis The Accretion History of Dark Matter Haloes by : Camila Anahi Correa
Download or read book The Accretion History of Dark Matter Haloes written by Camila Anahi Correa and published by . This book was released on 2016 with total page 203 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Book Synopsis The Astronomy Revolution by : Donald G. York
Download or read book The Astronomy Revolution written by Donald G. York and published by Taylor & Francis. This book was released on 2016-04-19 with total page 438 pages. Available in PDF, EPUB and Kindle. Book excerpt: Some 400 years after the first known patent application for a telescope by Hans Lipperhey, The Astronomy Revolution: 400 Years of Exploring the Cosmos surveys the effects of this instrument and explores the questions that have arisen out of scientific research in astronomy and cosmology. Inspired by the international New Vision 400 conference held
Book Synopsis Merger Histories of Dark Matter Halos in LambdaCDM and Implications for the Evolution of Milky Way-size Galaxies by : Kyle Robert Stewart
Download or read book Merger Histories of Dark Matter Halos in LambdaCDM and Implications for the Evolution of Milky Way-size Galaxies written by Kyle Robert Stewart and published by . This book was released on 2009 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: There is a concern in galaxy formation that mergers are too common in LambdaCDM to explain the prominence of thin disk-dominated galaxies in the local universe. In my dissertation, I analyze merger histories of dark matter halos from high resolution N-body simulations and compare dark halo merger statistics to the observable properties of galaxies, in order to study the implications of cosmologically motivated merger histories. I use empirical relations between a galaxy's dark matter halo mass, stellar mass, and cold gas mass to investigate these merger histories in the context of galaxy evolution, focusing on a dark matter mass regime within an order of magnitude of the Milky Way. The principle results of this dissertation may be summarized as follows. Firstly, 70% of Milky Way-size halos have accreted an object with more than twice the mass of the Milky-Way's disk in the past 10 Gyr. To meet the observed fraction of disk dominated galaxies, mergers of this size must not always destroy galactic disks. Secondly, The merger rate of dark halos increases strongly with redshift. A simple `universal' fitting formula describes these merger rates as a function of halo mass, merger mass ratio, and redshift. Thirdly, the fraction of halos have ever experienced a gas poor major merger roughly matches the observed early-type morphological fractions within the regime M=10^11-13 Msun, providing a possible solution to disk survivability, if gas rich mergers do not destroy disk-dominated morphologies. Fourthly, because the mapping between dark matter halo mass and galaxy stellar mass (or baryonic mass) is a non-trivial function, it is important to distinguish between definitions of a merger "mass ratio'' that use dark matter, stellar, or galaxy baryonic masses as a means of comparison. For example, major dark matter mergers in smaller galaxies (Mvir
Book Synopsis Dark Halo Merging and Galaxy Formation by : Risa H. Wechsler
Download or read book Dark Halo Merging and Galaxy Formation written by Risa H. Wechsler and published by . This book was released on 2001 with total page 586 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis From Supermassive Black Holes to Supersymmetric Dark Matter by : Savvas Michael Koushiappas
Download or read book From Supermassive Black Holes to Supersymmetric Dark Matter written by Savvas Michael Koushiappas and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: It is without doubt that in recent years cosmology has entered an era where cosmological parameters are now measured precisely enough to derive conclusions about the underlying characteristics of the Universe. I present an overview of the methods used to estimate the parameters that lead to the standard cosmological model. After a brief detour on the current understanding of the mechanisms that lead to galaxy formation, I present a model in which the seeds of supermassive black holes observed in galactic spheroids form out of the lowest angular momentum gas in proto-galaxies at high redshift. I assume that the gas in early-forming, rare-peak halos has a distribution of specific angular momentum similar to that derived for the dark matter. In halos more massive than a critical threshold, proto-galactic disks are gravitationally unstable and experience an efficient viscosity that transfers angular momentum outward allowing mass inflow. This process continues until the first massive stars disrupt the disk. The seed black holes created in this manner have a characteristic mass scale, roughly independent of the redshift of formation. By the redshift of reionization, the comoving mass density is comparable to that inferred from observations, with room for appropriate additional luminous growth during a later quasar accretion phase. The hierarchical merger process naturally leads to a linear correlation between black-hole mass and stellar spheroid mass. Quite orthogonal to this study, I estimate the probability of detecting gamma-rays from the annihilation of neutralino dark matter in the Milky Way substructure. I characterize substructure statistically based on Monte Carlo realizations of the formation of a Milky Way-like halo. I find that it may be possible for upcoming experiments to detect gamma-rays from dark matter substructure if the neutralino is relatively light, while for a heavy neutralino such a detection would be unlikely. I find that the probability of detection is sensitive to poorly-constrained input parameters, particularly those that characterize the primordial power spectrum. I conclude that the lack of a detected gamma-ray signal gives very little information about the supersymmetric parameter space due to uncertainties associated with both the properties of substructure and cosmological parameters.
Book Synopsis The Structure of Dark Matter Haloes in Cosmological Simulations by : Philip Edward Bett
Download or read book The Structure of Dark Matter Haloes in Cosmological Simulations written by Philip Edward Bett and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the angular momentum, shape and density structures of dark matter haloes using very large dark matter simulations, and use smaller, higher-resolution simulations to investigate how the distributions of these properties are changed by the physical processes associated with baryons and galaxy formation. We begin with a brief review of the necessary background theory, including the growth of cosmic structures, the origin of their angular momenta, and the techniques used to simulate galaxies, haloes and the large scale structure. In Chapter 2, we use the Millennium Simulation (MS) to investigate the distributions of the spin and shape parameters of millions of dark matter haloes. We compare results for haloes identified using three different algorithms, including one based on the branches of the halo merger trees. In addition to characterising the relationships between halo spin, shape and mass, we also study their impact on halo clustering and bias. We go on in Chapter 3 to investigate the internal angular momentum structure of dark matter haloes. We look at the radial profiles of the dark matter angular momentum in terms of both magnitude and direction, again using large-volume dark matter simulations including the MS. We then directly compare dark matter haloes simulated both with and without baryonic physics, studying how this changes the dark matter angular momentum. After relating the spin orientation of galaxies to their haloes, we consider the shape of the projected, stacked mass distribution of haloes oriented according to their central galaxy, mimicking attempts to measure halo ellipticity by weak gravitational lensing. We consider the density structure of dark matter haloes in Chapter 4. For the dark matter simulations, we focus our interest on the source of the scatter in the distribution of concentration parameters, correlating it with both the halo spin and formation time. We compare different algorithms for predicting the concentration distribution using different aspects of the merger histories. We again go on to directly compare high-resolution haloes in simulations run with and without baryons and galaxy formation, looking at how these additional physical processes transform the density profiles. Finally, we compare the circular velocity curves of the haloes simulated with galaxies to the rotation curves of observed galaxies, using the Universal Rotation Curve model.
Book Synopsis The Expected Shape of the Milky Way's Dark Matter Halo by : Jesús David Prada González
Download or read book The Expected Shape of the Milky Way's Dark Matter Halo written by Jesús David Prada González and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The shape of the Dark Matter (DM) structure (halo) in which a galaxy is embedded is heavily determined by the anisotropic accretion of mass from its specific environment. Therefore, the shape of a galaxy-s halo is an important feature to inquire about its formation history and the relation of DM and gas within it. In this work we study the shape of the DM halo of Milky Way-like galaxies from the Auriga simulations. We focus on the radial and time dependence. We found that, on DM-only and Magneto-hydrodynamic (MHD) simulations, the shape of the DM halo is more triaxial in the inner-skirts than in the outter-skirts. We compared simulations with and without gas and verified that the presence of visible matter has an effect of rounding the DM halo which is amplified for smaller radii, where the gravitational potential of the galactic disk becomes more significant. Regarding the effect of time...
Book Synopsis Cosmological Simulations of Galaxy Formation Including Hydrodynamics by : Francis Joseph Summers
Download or read book Cosmological Simulations of Galaxy Formation Including Hydrodynamics written by Francis Joseph Summers and published by . This book was released on 1993 with total page 774 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Formation Of The First Black Holes by : Muhammad Latif
Download or read book Formation Of The First Black Holes written by Muhammad Latif and published by World Scientific. This book was released on 2019-04-26 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt: The formation of the first supermassive black holes is one of the main open questions in our understanding of high-redshift structure formation. In this book, we aim to provide a summary of state-of-the-art modern research on this topic, exploring the formation of massive black holes from a fluid-dynamical, stellar-dynamical and chemical perspective. The book thus presents a solid theoretical foundation, a comparison with current observations and future observational perspectives with upcoming missions such as the Square Kilometre Array, the European Extremely Large Telescope, the Euclid satellite as well as possible detections via gravitational waves.
Book Synopsis Dynamics of the Milky Way by : Jason Sanders
Download or read book Dynamics of the Milky Way written by Jason Sanders and published by Springer. This book was released on 2015-06-15 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents a study of methods useful for modeling and understanding dynamical systems in the Galaxy. A natural coordinate system for the study of dynamical systems is the angle-action coordinate system. New methods for the approximation of the action-angle variables in general potentials are presented and discussed. These new tools are applied to the construction of dynamical models for two of the Galaxy’s components: tidal streams and the Galactic disc. Tidal streams are remnants of tidally stripped satellites in the Milky Way that experience the effects of the large scale structure of the Galactic gravitational potential, while the Galactic disc provides insights into the nature of the Galaxy near the Sun. Appropriate action-based models are presented and discussed for these components, and extended to include further information such as the metallicity of stars.
Book Synopsis Astrophysics in the Next Decade by : Harley A. Thronson
Download or read book Astrophysics in the Next Decade written by Harley A. Thronson and published by Springer Science & Business Media. This book was released on 2009-02-03 with total page 523 pages. Available in PDF, EPUB and Kindle. Book excerpt: NASA’s James Webb Space Telescope (JWST), planned for operation in about five years, will have the capability to investigate – and answer – some of the most challenging questions in astronomy. Although motivated and designed to study the very early Universe, the performance of the observatory’s instruments over a very wide wavelength range will allow the world’s scientific community unequaled ability to study cosmic phenomena as diverse as small bodies in the Solar System and the formation of galaxies. As part of preparation to use JWST, a conference was held in Tucson, Arizona in 2007 that brought together astronomers from around the world to discuss the mission, other major facilities that will operate in the coming decade, and major scientific goals for them. This book is a compilation of those presentations by some of the leading researchers from all branches of astronomy. This book also includes a “pre-history” of JWST, describing the lengthy process and some of the key individuals that initiated early work on the concepts that would evolve to become the premier space observatory of the next decade.
Book Synopsis Secular Evolution of Galaxies by : Jesús Falcón-Barroso
Download or read book Secular Evolution of Galaxies written by Jesús Falcón-Barroso and published by Cambridge University Press. This book was released on 2012 with total page 657 pages. Available in PDF, EPUB and Kindle. Book excerpt: The formation and evolution of galaxies is one of the most important topics in modern astrophysics. Secular evolution refers to the relatively slow dynamical evolution due to internal processes induced by a galaxy's spiral arms, bars, galactic winds, black holes and dark matter haloes. It plays an important role in the evolution of spiral galaxies with major consequences for galactic bulges, the transfer of angular momentum, and the distribution of a galaxy's constituent stars, gas and dust. This internal evolution is in turn the key to understanding and testing cosmological models of galaxy formation and evolution. Based on the twenty-third Winter School of the Canary Islands Institute of Astrophysics, this volume presents reviews from nine world-renowned experts on the observational and theoretical research into secular processes, and what these processes can tell us about the structure and formation of galaxies. The volume provides a firm grounding for graduate students and early career researchers working on galactic dynamics and galaxy evolution.
Book Synopsis New Horizons in Astronomy by : Astronomical Society of the Pacific
Download or read book New Horizons in Astronomy written by Astronomical Society of the Pacific and published by . This book was released on 2008 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt: "These are the proceedings of the 2007 Frank N. Bash Symposium, held at the University of Texas at Austin, USA, from October 14-16, 2007. The first "BashFest" was held in 2003 in honor of Professor Frank Bash at his retirement. Since then, the symposium has evolved into a bi-annual event featuring exclusively the research of young astronomers and astrophysicists from around the world." "The symposium centered around invited review talks by thirteen postdoctoral researchers covering the vast range of modern astronomical research, from the dynamics of small bodies in the Solar System, to globular clusters in the Milky Way and neighboring galaxies, to theories and observations of galaxy formation in the early Universe, and the instruments being designed for the thirty-meter class telescopes that will be used to study these diverse fields. Poster contributions from undergraduate and graduate students as well as postdoctoral researchers rounded out the conference. These posters also covered a wide variety of topics, including abundances in metal-rich and metal-poor stars, galaxy formation and evolution, multi-wavelength observations, and theoretical studies of supernovae and the early Universe." "These proceedings are suitable for young and experienced researchers alike who wish to view a snapshot of a wide range of astronomical topics as seen through the eyes of emerging scientists and framed by their vision of the future of the science of astronomy."--BOOK JACKET.
