Download or read book The Orbital Structure of Galaxies and Dark Matter Halos in N body Simulations written by Roland Jesseit and published by . This book was released on 2004 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Orbital Structure of Galaxies and Dark Matter Halos in N Body Simulations written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In dieser Arbeit werden zwei Entstehungmechanismen fuer Galaxien in N-Koerper Rechnungen untersucht. Unter der Annahme, dass die Teilchen in einem sphaerischen dunkle Materie Halo sich auf Kreisbahnen bewegen, macht die adiabatische Naeherung genaue Voraussagen ueber das Mass der Kontraktion des Halos waehrend der langsamen Scheibenbildung. Wir finden in N-Koerper Rechnungen, dass die adiabatische Naeherung fuer alle realistischen Massenverhaeltnisse zwischen Scheibe und Halo gilt, und Abweichungen von Kreisbahnen keine groessere Rolle spielen. Im zweiten Teil beschaeftigen wir uns mit der Entstehung von elliptischen Galaxien durch Verschmelzung von Scheibengalaxien. In einem Sample von 150 solcher Kollisionen klassifizieren wir die komplexe orbitale Struktur des Endergebnisses jeder Kollisionsrechnung. Die Klassifikation wird mit der Triaxialitaet und der Laenge der Haupttraegheitsachsen verknuepft, mit denen die Gestalt einer elliptischen Galaxie parametrisiert wird. Wir leiten daraus eine globale Besetzungswahrscheinlichkeit fuer selbstkonsistente triaxiale Galaxien ab, die mit theoretischen Erwartungen uebereinstimmt. Weiterhin finden wir, dass die Isophotenstruktur in den N-Koerperrechnungen nicht von einer Orbitgattung, sondern von einer ueberlagerung verschiedener Gattungen herruehrt. Die Dichotomie zwischen elliptischen Galaxien mit boxfoermigen und scheibenfoermigen Isophoten kann deswegen nicht vollstaendig auf eine Dominanz von box- bzw. scheibenfoermigen Orbits zurueckgefuehrt werden. Bisherige Simulationen koennen nicht beobachtete Korrelationen zwischen dem h_3 Parameter und der mittleren Geschwindigkeit reproduzieren. Als Ursache dieser Diskrepanz werden die box Orbits identifiziert, die in dissipationslosen Simulationen ueberproduziert werden. Z-tube Orbits erfuellen diese Korrelation jedoch sehr gut. Ebenso zeigt diese Komponente dieselbe Korrelation zwischen dem h_3 Parameter und v/sigma_0, wie beobachtete elliptische Galaxien. Wir schliessen darau.
Download or read book The Orbital Structure of Galaxies and Dark Matter Halos in N body Simulatons written by Roland Jesseit and published by . This book was released on 2004 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dark Matter Halos and Stellar Kinematics of Elliptical Galaxies written by Jeremy David Murphy and published by . This book was released on 2012 with total page 606 pages. Available in PDF, EPUB and Kindle. Book excerpt: The hierarchical assembly of mass, wherein smaller clumps of dark matter, stars, gas, and dust buildup over time to form the galaxies we see today in the local Universe through accretion events with other clumps, is a central tenet of galaxy formation theory. Supported by theoretically motivated simulations, and observations of the distribution of galaxies over a large range of redshift, the theory of hierarchical growth is now well established. However, on the scales of individual galaxies, hierarchical growth struggles to explain a number of observations involving the amount and distribution of dark matter in galaxies, and the timescale of both the formation of stars, and the assembly of those stars into galaxies. In this dissertation I attempt to address some of the central issues of galaxy formation. My work focuses on massive elliptical galaxies and employs the orbit-based, axisymmetric dynamical modeling technique of Schwarzschild to constrain the total mass of a galaxy to large radii. From this starting point a determination of the extent and shape of the dark matter halo profile is possible and can then be compared to the results of simulations of the formation of galaxies. These dynamical models include information on the stellar orbital structure of the galaxy, and can be used as a further point of comparison with N-body simulations and observations from other groups. Dynamical modeling results for both M49 and M87, the first and second rank galaxies in the Virgo Cluster, are presented and compared in Chapters 4 and 2 respectively. Although both galaxies are similar in mass, a closer analysis shows they exhibit very different dark matter halo profiles and stellar orbital structure, and likely followed very different formation pathways. My primary dataset comes from observations carried out on the Mitchell Spectrograph (formally VIRUS-P) at McDonald Observatory.\footnote{The instrument's name was changed over the last year. As some of this work was originally written when the instrument was named VIRUS-P, I have elected to use that name in those sections of this dissertation (Chapters 2 and 5). In Chapters 3, 4, and 6, I use the current name.} The Mitchell Spectrograph is a fiber-fed integral field spectrograph, and allows one to collect spectra at many positions on a galaxy simultaneously. With spectroscopy one is able to not only constrain the kinematics of the stars, but also their integrated chemical abundances. In the introduction I describe recent work I have carried out with my collaborators using the Mitchell Spectrograph to add further constraints to our picture of galaxy formation. In that work we find that the cores of massive elliptical galaxies have been in place for many billions of years, and had their star formation truncated at early times. The stars comprising their outer halos, however, come from less massive systems. Yet unlike the stars of present day, low-mass galaxies, whose star formation is typically extended, these accreted systems had their star formation shut off at high redshift. Although our current sample is relatively small, these observations place a rigid constraint on the timescale of galaxy assembly and indicate the important role of minor mergers in the buildup of the diffuse outer halos of these systems. All of these advances in our understanding of the Universe are driven, in large part, by advances in the instrumentation used to collect the data. The Mitchell Spectrograph is a wonderful example of such an advance, as the instrument has allowed for observations of the outer halo of M87 to unprecedented radial distances (Chapter 3). A significant component of my dissertation research has been focused on characterizing the fiber optics of both the Mitchell Spectrograph and the fiber optics for the VIRUS spectrograph. I cover the results of the work on the Mitchell Spectrograph optical fibers in Chapter 5. The affects of stress and motion on a fiber bundle, critical to the VIRUS spectrograph, are explored in Chapter 6.
Download or read book Mergers of Elliptical Galaxies and Dark Matter Halos written by Michael Robert Boylan-Kolchin and published by . This book was released on 2006 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Role of Halo Substructure in Gamma Ray Dark Matter Searches written by Miguel A. Sánchez-Conde and published by MDPI. This book was released on 2020-05-28 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: An important, open research topic today is to understand the relevance that dark matter halo substructure may have for dark matter searches. In the standard cosmological model, halo substructure or subhalos are predicted to be largely abundant inside larger halos, for example, galaxies such as ours, and are thought to form first and later merge to form larger structures. Dwarf satellite galaxies—the most massive exponents of halo substructure in our own galaxy—are already known to be excellent targets for dark matter searches, and indeed, they are constantly scrutinized by current gamma-ray experiments in the search for dark matter signals. Lighter subhalos not massive enough to have a visible counterpart of stars and gas may be good targets as well, given their typical abundances and distances. In addition, the clumpy distribution of subhalos residing in larger halos may boost the dark matter signals considerably. In an era in which gamma-ray experiments possess, for the first time, the exciting potential to put to test the preferred dark matter particle theories, a profound knowledge of dark matter astrophysical targets and scenarios is mandatory should we aim for accurate predictions of dark matter-induced fluxes for investing significant telescope observing time on selected targets and for deriving robust conclusions from our dark matter search efforts. In this regard, a precise characterization of the statistical and structural properties of subhalos becomes critical. In this Special Issue, we aim to summarize where we stand today on our knowledge of the different aspects of the dark matter halo substructure; to identify what are the remaining big questions, and how we could address these; and, by doing so, to find new avenues for research.
Download or read book Shapes Of Galaxies And Their Dark Halos The Proceedings Of The Yale Cosmology Workshop written by Priyamvada Natarajan and published by World Scientific. This book was released on 2002-03-28 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book constitutes the proceedings of a very topical workshop aimed at understanding the shapes of the baryonic and dark matter components of galaxies. Several groups presented their recent results from observations and numerical N-body simulations.
Download or read book Orbital Structure and Dark Matter Halos of Elliptical Galaxies written by Andi Kronawitter and published by . This book was released on 2000 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dark and Visible Matter in Galaxies written by Massimo Persic and published by . This book was released on 1997 with total page 632 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Shapes of Galaxies and Their Dark Halos written by Priyamvada Natarajan and published by World Scientific. This book was released on 2002 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book constitutes the proceedings of a very topical workshop aimed at understanding the shapes of the baryonic and dark matter components of galaxies. Several groups presented their recent results from observations and numerical N-body simulations.
Download or read book N body Simulations of Galaxies and Halos in Cold Dark Matter Models written by Stylianos Kazantzidis and published by . This book was released on 2005 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Coupling Semi analytic Models and N body Simulations written by Krista McCord and published by . This book was released on 2017 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stellar halos give insight into the initial conditions that existed when a host galaxy first formed and provide details on disrupted satellites via their different stellar populations. An algorithm that is computationally inexpensive compared to hydrodynamic simulations is necessary in order to theoretically study the structure and formation of galactic stellar halos in sufficient detail to probe substructure. CoSANG (Coupling Semi-Analytic/N-body Galaxies) is a new computational method that we are developing which couples pure dark matter N-body simulations with a semi-analytic galaxy formation model. At each timestep, results from the N-body simulation feed into the semi-analytic code, whose results feed back into the N-body code making the evolution of the dark matter and baryonic matter dependent on one another. CoSANG will enable a variety of galaxy formation science, including analysis of stellar populations, halo merging, satellite accretion, supermassive black holes, and indirect and direct dark matter detection. In this dissertation, I will describe the new simulation code CoSANG. The results from the extensive testing phase on CoSANG will be presented which indicate CoSANG is properly simulating feedback from galaxies within a dark matter halo. I used this validated code to analyze a CoSANG zoom simulation of a $10^12 M⊙ dark matter halo. Results showed a flatter inner halo near the disk and a more spherical outer halo which is expected when a galaxy exists at the center of a dark matter halo. A comparison is made with a simulation run with the same initial conditions, but with the baryonic component simulated using a hydrodynamic algorithm. The semi-analytic model predicted galaxy types better than the hydrodynamic simulation leading to the conclusion that the CoSANG halo is more accurate. I also present a dark matter direct detection analysis on the CoSANG zoom halo to measure the dark matter velocity distributions and modulation amplitudes. The CoSANG results show that the dark matter velocity distribution does not fit well to a Maxwell Boltzmann distribution and the modulation amplitudes derived indicate an anisotropic dark matter velocity distribution. Future work will include tagging dark matter particles with stellar properties to build and evolve a stellar halo.
Download or read book The Equilibrium Structure of Dark Matter Halos written by Michael Travis Busha and published by . This book was released on 2007 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Simulations of Galaxy Formation and Large Scale Structure written by Felix Stoehr and published by Sudwestdeutscher Verlag Fur Hochschulschriften AG. This book was released on 2009-12 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this work we use the N-body resimulation technique to address aspects of structure formation. In the first chapter we study the influence of the local environment of DM haloes on their properties. In the second chapter we address the so-called "substructure problem" which is one of the major challenges of the CDM model of cosmology. We perform ultra-high resolution simulations of the assembly of a Milky Way type dark matter halo within its full cosmological context and propose a new analytical fitting formula (SWTS) which provides a better fit to the simulated Milky Way halo than the NFW or Moore profiles do. In the third chapter we use our ultra-high resolution simulations to study the possible -ray signal from dark matter annihilation. If such a signal was detected, the nature of the dark matter, the answer to one of the most important questions of modern cosmology, would be known. (urn: nbn: de: bvb:19-16446)"
Download or read book Understanding the Formation and Evolution of Nuclei in Galaxies Using N body Simulations written by Markus Hartmann and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Central massive objects like supermassive black holes and stellar nuclear clusters are common in all type of galaxies. I use N-body simulations to study the formation and evolution of nuclear clusters and to investigate the influence of the dynamical evolution of disc galaxies on the structural and kinematical properties of the host galaxy. I show that the second moment of velocities determine a lower limit on the dissipative formation process, which is about 50% in the case of the nuclear cluster in the late-type spiral galaxy NGC 4244. The vertical anisotropy of nuclear clusters can be used to determine an upper limit on the formation process due to merger or accretion of star clusters, which is about 10% for the nuclear cluster in NGC 4244. This is the first time that we have strong evidence of a hybrid formation scenario for nuclear clusters. In a set of 25 galaxy simulations I study bar formation in disc galaxies. I show that bar formation lead to the increase in mass in the central region of galaxies. This mass increase raises the velocity dispersion of stars in the disc and bulge component, which explains the offset of barred galaxies in the relation between the mass of the supermassive black hole, M., and the velocity dispersion of stars in the bulge, [delta]e, the M. - [delta]e relation (Gueltekin et al. 2009). While Graham et al. (2011) argued that the orbital structure of stars within the bar could be responsible for the observed offset of barred galaxies from the M. - [delta]e relation of unbarred galaxies, I show that the effect of stellar orbits in bars on [delta]e is less than 15% compared to the increase in mass which raises [delta]e by 40%. The offset I find in the simulation is comparable to the offset using the recent sample of M. measurements of elliptical, unbarred and barred disc galaxies from Gueltekin et al. (2009).
Download or read book Dark Matter Halo Concentration and the Evolution of Spiral Structure in N body Barred Spiral Galaxies written by Jazmin Esmeralda Berlanga Medina and published by . This book was released on 2015 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: Motivated by the evidence of relationships between pitch angle (the tightness of spiral arm structure in the disk), P, and various indicators of central mass concentration, as well as the theoretical relationship between halo mass concentration and the density of visible matter in the central part of the galaxy, we look at a possible relationship between P and cvir. (the virial concentration of the dark matter halo) in N-body simulations of barred, spiral galaxies. We also look at the evolution of pitch angle over time in higher temporal resolution than any data currently available in the literature. We find that pitch angle structure is recurring, the overall distribution staying within a relatively narrow range. We do not find evidence for a relation between P and cvir.
Download or read book Probing Local Group Galactic Substructure with Cosmological Simulations written by Gregory Alan Dooley and published by . This book was released on 2017 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Lambda cold dark matter (ACDM) model is enormously successful at predicting large scale structure in the Universe. However, some tensions still remain on small scales, specifically regarding observed satellites of the Milky Way (MW) and Andromeda. Foremost among the problems have been the missing satellite, too big to fail, and cusp/core problems, which concern the expected abundance of satellites and their inner structure. This Ph.D. thesis consists of a series of studies using dark matter only cosmological N-body simulations of MW-mass galaxies to address topics related to these issues. In light of the recent Planck mission, I investigate how changes to cosmological parameters affect dark matter halo substructure. I find that the process of continuous sub-halo accretion and destruction leads to a steady state description of most subhalo properties in a given host, unchanged by small fluctuations in cosmological parameters. Subhalo concentration, maximum circular velocity, and formation times, however, are somewhat affected. One way to reduce the central density of satellites, as needed to solve the cusp/core and too big to fail problems, is through self-interacting dark matter (SIDM). I search for new implications of SIDM and find that stars in satellites spread out to larger radii and are tidally stripped at a higher rate in SIDM than CDM, even though the mass loss rate of dark matter is unchanged. These signatures should be particularly prominent in ultrafaint dwarf galaxies for the class of otherwise difficult to constrain velocity-dependent SIDM models. I also helped carry out the Caterpillar project, a suite of 36 high mass resolution (~ 10' Mo/particle) simulations of MW-like galaxies used to study diversity in halo substructure. To these, I apply abundance matching and reionization models to make novel predictions about the abundance of satellites in isolated dwarf galaxies out to 8 Mpc to help guide future searches. Applying the same techniques to predict satellites within 50 kpc of the LMC, I discover large discrepancies with the observed stellar mass function, which may lead to new constraints on the galaxy stellar mass-halo mass relationship, and the ability of reionization to leave dark matter halos entirely dark.
