Browsing by Subject "anisotropy-probe observations"
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Item Extracting Angular Diameter Distance And Expansion Rate Of The Universe From Two-Dimensional Galaxy Power Spectrum At High Redshifts: Baryon Acoustic Oscillation Fitting Versus Full Modeling(2009-03) Shoji, Masatoshi; Jeong, Donghui; Komatsu, Eiichiro; Shoji, Masatoshi; Jeong, Donghui; Komatsu, EiichiroWe present a method for extracting the angular diameter distances, D(A), and the expansion rates, H, of the universe from the two-dimensional baryon acoustic oscillations (BAO) in the galaxy power spectrum. Our method builds upon the existing algorithm called the "fit-and-extract" (FITEX) method, which allows one to extract only D(A)(2)/H from a spherically averaged one-dimensional power spectrum. We develop the FITEX-2d method, an extension of the FITEX method, to include the two-dimensional information, which allows us to extract D(A) and H simultaneously. We test the FITEX-2d method using the Millennium Simulation as well as simplified Monte Carlo simulations with a bigger volume. The BAOs, however, contain only a limited amount of information. We show that the full modeling, including the overall shape of the power spectrum, yields much better determinations of D(A) and H, hence the dark energy equation of Stateparameters such as w(0) and w(a), than the BAO-only analysis by more than a factor of 2, provided that nonlinear effects are under control.Item First-Year Sloan Digital Sky Survey-II (SDSS-II) Supernova Results: Constraints On Nonstandard Cosmological Models(2009-10) Sollerman, Jesper; Mortsell, E.; Davis, T. M.; Blomqvist, M.; Bassett, Bruce; Becker, A. C.; Cinabro, David; Filippenko, Alexei V.; Foley, Ryan J.; Frieman, J.; Garnavich, Peter; Lampeitl, Hubert; Marriner, J.; Miquel, Ramon; Nichol, Robert C.; Richmond, M. W.; Sako, Masao; Schneider, Donald P.; Smith, Mathew; Vanderplas, J. T.; Wheeler, J. Craig; Wheeler, J. CraigWe use the new Type Ia supernovae discovered by the Sloan Digital Sky Survey-II supernova survey, together with additional supernova data sets as well as observations of the cosmic microwave background and baryon acoustic oscillations to constrain cosmological models. This complements the standard cosmology analysis presented by Kessler et al. in that we discuss and rank a number of the most popular nonstandard cosmology scenarios. When this combined data set is analyzed using the MLCS2k2 light-curve fitter, we find that more exotic models for cosmic acceleration provide a better fit to the data than the.CDM model. For example, the flat Dvali-Gabadadze-Porrati model is ranked higher by our information-criteria (IC) tests than the standard model with a flat universe and a cosmological constant. When the supernova data set is instead analyzed using the SALT-II light-curve fitter, the standard cosmological-constant model fares best. This investigation of how sensitive cosmological model selection is to assumptions about, and within, the light-curve fitters thereby highlights the need for an improved understanding of these unresolved systematic effects. Our investigation also includes inhomogeneous Lemaitre-Tolman-Bondi (LTB) models. While our LTB models can be made to fit the supernova data as well as any other model, the extra parameters they require are not supported by our IC analysis. Finally, we explore more model-independent ways to investigate the cosmic expansion based on this new data set.Item Fragmentation In The First Galaxies(2010-11) Safranek-Shrader, Chalence; Bromm, Volker; Milosavljevic, Milos; Safranek-Shrader, Chalence; Bromm, Volker; Milosavljevic, MilosMotivated by recent simulations of galaxy formation in which protogalaxies acquire their baryonic content through cold accretion, we study the gravitational fragmentation of cold streams flowing into a typical first galaxy. We use a one-zone hydrodynamical model to examine the thermal evolution of the gas flowing into a 10(8) M(circle dot) dark matter halo at redshift z = 10. The goal is to gain an understanding of the expected fragmentation mass scale and thus the characteristic mass of the first population of stars to form by shock fragmentation. Our model accurately describes the chemical and thermal evolution of the gas as we are specifically concerned with how the chemical abundances and initial conditions of the low-density, metal-enriched, cold accretion streams that pass an accretion shock alter the cooling properties and tendency to fragment in the post-shock gas. Cold accretion flows are not shock heated at the virial radius but instead flow along high-baryonic-density filaments of the cosmic web and penetrate deep into the host halo of the protogalaxy. In this physical regime, if molecular cooling is absent because of a strong Lyman-Werner background, we find there to be a sharp drop in the fragmentation mass at a metallicity of Z similar to 10(-4) Z(circle dot). If, however, H(2) and HD molecules are present, they dominate the cooling at T < 10(4) K, and metallicity then has no effect on the fragmentation properties of the cold stream. For a solar abundance pattern of metallicity, O is the most effective metal coolant throughout the evolution, while for a pair instability supernova (PISN) metallicity yield, Si(+) is the most effective coolant. PISN abundance patterns also exhibit a slightly smaller critical metallicity. Dust grains are not included in our chemical model, but we argue that their inclusion would not significantly alter the results. We also find that this physical scenario allows for the formation of stellar clusters and large, 10(4) M(circle dot) bound fragments, possibly the precursors to globular clusters and supermassive black holes. Finally, we conclude that the usual assumption of isobaricity for galactic shocks breaks down in gas of a sufficiently high metallicity, suggesting that metal cooling leads to thermal instabilities.