2001 (IPP)
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Item How to distinguish a nearly flat Universe from a flat Universe using the orientation independence of a comoving standard ruler(2001-01-20) Roukema, B. F.Several recent observations using standard rulers and standard candles now suggest, either individually or in combination, that the Universe is close to flat, i.e. that the curvature radius is about as large as the horizon radius (∼ 10h−1 Gpc) or larger. Here, a method of distinguishing an almost flat universe from a precisely flat universe using a single observational data set, without using any microwave background information, is presented. The method (i) assumes that a standard ruler should have no preferred orientation (radial versus tangential) to the observer, and (ii) requires that the (comoving) length of the standard ruler be known independently (e.g. from low redshift estimates). The claimed feature at fixed comoving length in the power spectrum of density perturbations, detected among quasars, Lyman break galaxies or other high redshift objects, would provide an adequate standard candle to prove that the Universe is curved, if indeed it is curved. For example, a combined intrinsic and measurement uncertainty of 1% in the length of the standard ruler L applied at a redshift of z = 3 would distinguish an hyperbolic (Ωm = 0.2,ΩΛ = 0.7) or a spherical (Ωm = 0.4, ΩΛ = 0.7) universe from a flat one to 1 − P > 95% confidenceItem On the comoving distance as arc-length in four dimensions(2001-08-04) Roukema, B. F.The inner product provides a conceptually and algorithmically simple method for cal- culating the comoving distance between two cosmological objects given their redshifts, right ascension and declination, and arbitrary constant curvature. The key to this is that just as a distance between two points ‘on’ the surface of the ordinary 2-sphere S2 is simply an arc-length (angle multiplied by radius) in ordinary Euclidean 3-space E3, the distance between two points ‘on’ a 3-sphere S3 (a 3-hyperboloid H3) is simply an ‘arc-length’ in Euclidean 4-space E4 (Minkowski 4-spaceM4), i.e. an ‘hyper-angle’ multiplied by the curvature radius of the 3-sphere (3-hyperboloid).Item Cosmological Constant and Quintessence from a Correlation Function Comoving Fine Feature in the 2dF Quasar Redshift Survey(2001-06-05) Roukema, B. F.; Mamon, G. A.Local maxima at characteristic comoving scales have previously been claimed to exist in the density perturbation spectrum at the wavenumber k = 2π/LLSS, where LLSS ∼ 100–200 h−1 Mpc (comoving), at low redshift (z < ∼0.4) for several classes of tracer objects, at z ≈ 2 among quasars, and at z ≈ 3 among Lyman break galaxies. Here, this cosmic standard ruler is sought in the “10K” initial release of the 2dF QSO Redshift Survey (2QZ-10K), by estimating the spatial two-point autocorrelation functions ξ(r) of the three-dimensional (comoving, spatial) distribution of the N = 2378 quasars in the most completely observed and “covered” sky regions of the catalogue, over the redshift ranges 0.6 < z < 1.1 (“low-z”), 1.1 < z < 1.6 (“med-z”) and 1.6 < z < 2.2 (“hi-z”). Because of the selection method of the survey and sparsity of the data, the analysis was done conservatively to avoid non-cosmological artefacts. (i) Avoiding a priori estimates of the length scales of features, local maxima in ξ(r) are found in all three different redshift ranges. The requirement that a local maximum be present in all three redshift ranges at a fixed comoving length scale implies strong, purely geometric constraints on the local cosmological parameters, in which case the length scale of the local maximum common to the three redshift ranges is 2LLSS = 244±17 h−1 Mpc. (ii) For a standard cosmological constant FLRW model, the matter density and cosmological constant are constrained to Ωm = 0.25 ± 0.10, ΩΛ = 0.65±0.25 (68% confidence), Ωm = 0.25±0.15, ΩΛ = 0.60±0.35 (95% confidence), respectively, from the 2QZ-10K alone. Independently of the type Ia supernovae data, the zero cosmological constant model (ΩΛ = 0) is rejected at the 99.7% confidence level. (iii) For an effective quintessence (wQ) model and zero curvature, wQ < −0.5 (68% confidence), wQ < −0.35 (95% confidence) are found, again from the 2QZ-10K alone. In a different analysis of a larger (but less complete) subset of the same 2QZ-10K catalogue, Hoyle et al. (2001) found a local maximum in the power spectrum to exist for widely differing choices of Ωm and ΩΛ, which is difficult to understand for a genuine large scale feature at fixed comoving length scale. A resolution of this problem and definitive results should come from the full 2QZ, which should clearly provide even more impressive constraints on fine features in density perturbation statistics, and on the local cosmological parameters Ωm, ΩΛ and wQItem Cosmic Microwave Background Anisotropy Measurement from Python V(2001-03-01) Coble, Kim; Dodelson, S.; Dragovan, Mark; et al.We analyze observations of the microwave sky made with the Python exper- iment in its fifth year of operation at the Amundsen-Scott South Pole Station in Antarctica. After modeling the noise and constructing a map, we extract the cosmic signal from the data. We simultaneously estimate the angular power spectrum in eight bands ranging from large (ℓ ∼ 40) to small (ℓ ∼ 260) angular scales, with power detected in the first six bands. There is a significant rise in the power spectrum from large to smaller (ℓ ∼ 200) scales, consistent with that ex- pected from acoustic oscillations in the early Universe. We compare this Python V map to a map made from data taken in the third year of Python. Python III observations were made at a frequency of 90 GHz and covered a subset of the region of the sky covered by Python V observations, which were made at 40 GHz. Good agreement is obtained both visually (with a filtered version of the map) and via a likelihood ratio test.