Browsing by Subject "Dark matter"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
Item Cosmology with Bose-Einstein-condensed scalar field dark matter(2013-05) Li, Bohua, Ph. D.; Shapiro, Paul R.Despite the great successes of the Cold Dark Matter (CDM) model in explaining a wide range of observations of the global evolution and the formation of galaxies and large-scale structure in the universe, the origin and microscopic nature of this dark matter is still unknown. The most common form of CDM considered to-date is that of Weakly Interacting Massive Particles (WIMPs), but some of the cosmological predictions for this kind of CDM are in apparent conflict with observations (e.g. cuspy-cored halos and an overabundance of satellite dwarf galaxies). For these reasons, it is important to consider the consequences of different forms of CDM. We focus here on the hypothesis that the dark matter is comprised, instead, of ultralight bosons that form a Bose-Einstein Condensate (BEC), described by a complex scalar field. We start from the Klein-Gordon and Einstein field equations to describe the evolution of the Friedmann-Robertson-Walker (FRW) universe in the presence of this kind of dark matter. We find that, in addition to the phases of radiation-domination (RD), matter-domination (MD) and Lambda-domination (LD) familiar from the standard CDM model, there is an earlier phase of scalar-field-domination (SFD) which is special to this model. In addition, while WIMP CDM is non-relativistic at all times after it decouples, the equation of state of BEC-SFDM is found to be relativistic at early times, evolving from incompressible ($\bar{p} = \bar{\rho}$) to radiation-like ($\bar{p} = \bar{\rho}/3$), before it becomes non-relativistic and CDM-like at late times. The timing of the transitions between these phases and regimes is shown to yield fundamental constraints on the particle mass and self-interaction coupling strength. We also discuss progress on the description of structure formation in this model, which includes additional constraints on these parameters.Item Dark matter halos and stellar kinematics of elliptical galaxies(2012-08) Murphy, Jeremy David; Hill, Gary J.; Gebhardt, Karl; Cappellari, Michele; Kormendy, John; MacQueen, Phillip; Milosavljevic, MilosThe 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.Item Dynamic and spatial properties of satellites in isolated galactic systems(Texas Tech University, 2006-12) Diaz, Abel B.; Wilhelm, Ronald; Thacker, Beth Ann; Hatfield, Lynn L.Using the NYU Value-Added Galaxy Catalog (NYU-VAGC) I examine the line-of-site velocity dispersion of satellite galaxies orbiting larger, isolated, primary galaxies. The line-of-sight dispersion can be directly compared to the functional form of three models (NFW, MOND and a relic neutrino based model) that diverge at large distances allowing discrimination between models. The algorithm used to determine the primary and satellite samples yielded 2741 primary galaxies and 4966 possible satellites. After removing foreground/background interloper galaxies, I found the NFW model is the most probable. This agrees well with other published results which find that the density of the dark matter halo declines as p µ r-3. The neutrino model has large probabilities and cannot be completely excluded as a possible explanation of the observed velocity dispersions. The MOND model had small probabilities of fitting the velocity dispersion, and results of higher dispersions found for early type primaries than those found for late type primaries of the same luminosity make MOND unlikely. From the data I find no evidence of the Holmberg Effect. Satellite galaxies tend to be isotropic both at small projected distances from the primary galaxy and at large projected distances (at the 1 sigma level) from the primary galaxy. However, I do find that the distribution of early type satellites tends to decline more steeply than the late type satellites in a high magnitude primary sample.Item Exploring the dynamics and dark halos of elliptical galaxies at large radii(2009-08) Forestell, Amy Dove; Gebhardt, KarlDark matter is now accepted as an integral part of our universe, and galaxy dynamics have long provided the most convincing observational evidence for dark matter. Spiral galaxies have traditionally been used for these studies because of their more simple kinematics, however elliptical galaxies need to be understood as well. In this dissertation I present deep long-slit spectroscopy from the University of Texas’ Hobby-Eberly Telescope for a sample of elliptical galaxies. For a subsample of galaxies I fit axisymmetric orbit-superposition models with a range of dark halo density profiles. I find that all three galaxies modeled require a significant dark halo to explain their motions. However, the shape of the dark halo is not the expected NFW profile, but rather a profile with a flat central slope. I also discuss the galaxy masses, anisotropies, and stellar mass-to-light ratios.Item The imprint of the ionized intergalactic medium on the temperature anisotropy of the cosmic microwave background and the mutual-impact of reionization and small-scale structure(2015-08) Park, Hyunbae; Shapiro, Paul R.; Komatsu, Eiichiro; Finkelstein, Steven; Milosavljevic, Milos; Kumar, PawanIonized intergalactic medium (IGM) is an important component in cosmic history. After recombination, the universe went though a dark age until the first stars formed. Since the formation of the first stars, the ionized gas, on one hand, played an important role in the history of the universe and, on the other hand, left its imprints on observables that current and future experiments can measure. In this dissertation, we discuss both of each aspects about ionized gas. First, we discuss the mutual-impact of reionization and the IGM in small-scale structures. While reionization took place preferentially from densest regions of the universe, IGM in average density regions is expected to have been ionized externally by galaxies formed in denser regions. Until ionized by external radiation, the IGM is expected to have grown numerous small-scale structures. We simulate how the hydrodynamic feedback on the small-scale structures and its impact on recombination. Then, we also discuss our result on how recombination can impact on the global progress of the reionization. Compared to previous works, we improve on the resolution of simulation. Previous studies took into account only the structures that can form in photoionized gas down to 10⁸ M [sun symbol] in mass. Here, we present a study that resolves halos down to 10⁴ M [sun symbol] to account for structures that were able to form before the reionization heats the gas. Second, we discuss the kinetic Sunyaev-Zel'dovich effect on the Cosmic Microwave Background (CMB) : temperature fluctuations via the Doppler shift induced by the line-of-sight (LOS) component of the momentum of electrons in the ionized IGM. For the EoR contribution to the signal, we calculate the expected signal from simulations of cosmic reionization that, for the first time, includes the effect of "self-regulation" of reionization: star formation in low-mass galaxies (10⁸ M [sun symbol] [less than or equal to] M [subscript halo] [less than or equal to] 10⁹ M [sun symbol]) and minihalos (10⁵ M [sun symbol] [less than or equal to] M [subscript halo] [less than or equal to] 10⁸ M [sun symbol]) is suppressed if these halos form in regions that are already ionized or Lyman-Werner dissociated. For the post-reionization signal, we revisit the currently used model for non-linear transverse momentum power spectrum with a particular emphasis on the connected term that has been neglected in the literature.Item Integral field spectroscopy as a probe of galaxy evolution(2011-08) Adams, Joshua Jesse; Gebhardt, Karl; Hill, Gary J.; Drory, Niv; Evans, Neal; Bromm, VolkerOptical spectroscopy and modeling are applied to four independent problems related to the structure and evolution of galaxies. The problems cover a broad range of look-back time and galaxy mass. Integral field spectroscopy with low surface brightness sensitivity is the tool employed to advance our understanding of the distribution, interplay, and evolution of the stars, dark matter, and gas. First, I review development and commissioning work done on the VIRUS-P instrument. I then present a large sample of galaxies over redshifts 1.9= 10E12 solar masses). Third, I study the dark matter halo profile in a nearby late-type dwarf galaxy in the context of the "core-cusp" controversy. N-body simulations predict such galaxies to have cuspy dark matter halos, while HI rotation curves and more recent hydrodynamical simulations indicate that such halos may instead be strongly cored. I measure the spatially resolved stellar velocity field and fit with two-integral Jeans models. A cuspy halo is preferred from the stellar kinematics. The mass models from stellar and gaseous kinematics disagree. The gas models assume circular motion in an infinitely thin disk which is likely unrealistic. The stellar kinematics presented are the first measurements of a collision-less tracer in such galaxies. Fourth, I attempt to measure diffuse H-alpha emission, fluoresced by the metagalactic UV background, in the outskirts of a nearby gas rich galaxy. I do not make a detection, but the deep flux limit over a large field-of-view places the most sensitive limit to-date on the UV background's photoionization rate of Gamma(z=0)<1.7x10E-14 1/s at 5 sigma certainty.Item Measuring dark matter profiles non-parametrically in dwarf spheroidal galaxies(2014-05) Jardel, John Raymond; Gebhardt, KarlAlthough exotic objects like supermassive black holes (SMBHs) and dark matter halos do not emit or interact with light, we can still detect them across the vastness of space. By observing the gravitational dance of objects we can see, astronomers are able to infer the mass of the invisible objects they orbit. This has led to the discovery that nearly every massive galaxy hosts a SMBH at its center, and has confirmed that every galaxy is embedded in an extended halo of dark matter. However, the practice of inferring mass from the motions of bright kinematics tracers has many complications, not the least of which is that we seldom observe more than the line-of-sight component of the instantaneous velocity of a star. Consequently, astronomers must build dynamical models of the galaxies they wish to study. These models often rely on overly restrictive assumptions, or are crippled by degeneracies amongst their parameters and lack predictive power. In this thesis, I introduce a significant advancement into the field of dynamical modeling. My modeling technique is based on the powerful principle of orbit superposition, also known as Schwarzschild Modeling. This technique is robust to many of the degeneracies associated with dynamical modeling, and has enjoyed much success in measuring the SMBHs and dark matter halos of large elliptical or bulge-dominated galaxies. I use it in Chapter 2 to accurately measure the SMBH in the Sombrero Galaxy (NGC 4594) and to constrain its dark matter halo. Unfortunately, when measuring dark matter halos with Schwarzschild Modeling, the modeler is required to adopt a parameterization for the dark matter density profile. Often this is precisely the quantity one wishes to measure. To avoid this reliance on a priori parameterizations, I introduce a technique that calculates the profile non-parametrically. Armed with this powerful new technique, I set out to measure the distribution of dark matter in the halos of some of the smallest galaxies in the Universe. These dwarf spheroidal galaxies (dSphs) orbit the Milky Way as satellites, and their dark matter content has been studied extensively. However, the models used to probe their halos have been simplistic and required overly restrictive assumptions. As a result, robust conclusions about their dark matter content have remained elusive. Into this controversial and active area of study, I bring Non-Parametric Schwarzschild Modeling. The results I find offer the most robust and detailed measurements of the dark matter profiles in the dSphs to date. I begin my study with the first application of standard Schwarzschild Modeling to any dSph galaxy by using it in Chapter 3 on Fornax. This chapter details the process of re-tooling Schwarzschild Modeling for the purpose of measuring these small galaxies. In Chapter 4, I introduce the fully non-parametric technique, and apply it to Draco as proof of concept. Chapter 5 presents the main results of this thesis. Here I apply Non-Parametric Schwarzschild Modeling to Draco, Carina, Fornax, Sculptor, and Sextans. By relaxing the assumption of a parameterization for the dark matter profile, I find a variety of profile types in these five galaxies---some of which are consistent with past observations, others consistent with predictions from simulations, and still others were completely unanticipated. Finally, in Chapter 6 I describe the modeling of these galaxies in more detail. I demonstrate the accuracy of Non-Parametric Schwarzschild Modeling by recovering a known dark matter profile from artificial simulated data. I also expound upon the modeling results by presenting the detailed orbit structure of the five dSphs. Lastly, I compare my results to hydrodynamical simulations to explore the link between dark matter profile type and the baryon content of the dSphs.Item Modeling and constraining inflationary and pre-inflationary eras(2016-08) Aravind, Aditya; Paban, Sonia; Fischler, Willy; Distler, Jacques; Kilic, Can; Shapiro, Paul RThe paradigm of cosmic inflation has had great success in explaining the statistical properties of fluctuations in the Cosmic Microwave Background (CMB). In this dissertation we discuss a few avenues for modeling and constraining the inflationary universe - constraints on excited states of inflationary fluctuations, some aspects of multi-field tunneling and also constraints on and predictions from a specific model of inflation connecting Higgs physics and dark matter. First, we show that in standard single field slow roll inflation, Bogoliubov excitations of the fluctuation spectrum are tightly constrained by observations. These constraints ensure that the squeezed limit non-gaussianity obtained from such excited states cannot be large. They also rule out any significant imprints in the CMB coming from a sudden transition from kinetic energy domination to inflation. We then explore tunneling in the context of field theory, a scenario that has potential relevance to the pre-inflationary universe. We discuss subtleties involved in choosing the trajectory for tunneling out of a metastable vacuum in a multi-field potential. In particular, we use exact solutions and scaling relations to show that tunneling may happen along directions with large barriers, thus making the common intuition coming from quantum mechanical tunneling unreliable in estimating the tunneling trajectory and therefore, the bounce action. We then explore a specific model of inflation that involves the addition of a scalar singlet and fermionic dark matter to the standard Higgs inflation scenario. We show that dark matter constraints and the requirement to support successful inflation significantly constrain the available parameter space for this model. We also find that the model generically predicts a small value of the tensor-to-scalar ratio r, similar to standard Higgs inflation, though it allows for a larger range of values for the scalar spectral tilt nS.Item Two non-traditional applications of orbit-based modeling(2010-08) Jardel, John Raymond; Gebhardt, Karl; Kormendy, John; Milosavljevic, Milos; Shapiro, PaulOrbit-based modeling is a powerful way to construct dynamical models of galaxies. It has been used to measure the masses of supermassive black holes (SMBHs), constrain dark matter halos, and to recover information about the orbit structure of galaxies. This type of modeling usually goes hand in hand with the study of elliptical galaxies, however its applicability extends much further than this. In this thesis, I apply the well-studied technique of orbit-based modeling to two different types of galaxies—NGC 4594 (Sa) and Fornax (dSph). In NGC 4594, I use orbit-based models to update the mass of the central SMBH, place new constraints on its dark matter halo, and analyze the internal moments of its distribution function. For Fornax, the focus is to determine the shape of the dark matter density profile as well as to learn what we can from the internal moments.