Showing papers by "Lloyd Knox published in 2001"

Bayesian methods for cosmological parameter estimation from cosmic microwave background measurements

Abstract: We present a strategy for a statistically rigorous Bayesian approach to the problem of determining cosmological parameters from the results of observations of anisotropies in the cosmic microwave background. Our strategy relies on Markov chain Monte Carlo methods, specifically the Metropolis-Hastings algorithm, to perform the necessary high-dimensional integrals. We describe the Metropolis-Hastings algorithm in detail and discuss the results of our test on simulated data.

Probing Early Structure Formation with Far-Infrared Background Correlations

Abstract: The large-scale structure of high-redshift galaxies produces correlated anisotropy in the far-infrared background (FIRB). In regions of the sky where the thermal emission from Galactic dust is well below average, these high-redshift correlations may be the most significant source of angular fluctuation power over a wide range of angular scales, from ~7' to ~3°, and frequencies, from ~400 to ~1000 GHz. The strength of this signal should allow detailed studies of the statistics of the FIRB fluctuations, including the shape of the angular power spectrum at a given frequency and the degree of coherence between FIRB maps at different frequencies. The FIRB correlations depend on and hence constrain the redshift-dependent spectral energy distributions, number counts, and clustering bias of the galaxies and active nuclei that contribute to the background. We quantify the accuracy to which Planck and a newly proposed balloon-borne mission, Explorer of Diffuse Galactic Emissions, could constrain models of the high-redshift universe through the measurement of FIRB fluctuations. We conclude that the average bias of high-redshift galaxies could be measured to an accuracy of 1% or, for example, separated into four redshift bins with ~10% accuracy.

The angular power spectrum of edinburgh/durham southern galaxy catalogue galaxies

Abstract: We determine the angular power spectrum Cl of the Edinburgh/Durham Southern Galaxy Catalogue (EDSGC) and use this statistic to constrain cosmological parameters. Our methods for determining Cl and the parameters that affect it are based on those developed for the analysis of cosmic microwave background maps. We expect them to be useful for future surveys. Assuming flat cold dark matter models with a cosmological constant (constrained by the COBE Differential Microwave Radiometer experiment and local cluster abundances) and a scale-independent bias b, we find acceptable fits to the EDSGC angular power spectrum with 1.11 < b < 2.35 and 0.2 < Ωm < 0.55 at 95% confidence. These results are not significantly affected by the "integral constraint" or extinction by interstellar dust but may be by our assumption of Gaussianity.

Cmb power spectrum estimation via hierarchical decomposition

Abstract: We have developed a fast, accurate and generally applicable method for inferring the power spectrum and its uncertainties from maps of the cosmic microwave background in the presence of inhomogeneous and correlated noise. For maps with ${10}^{4}$ to ${10}^{5}$ pixels, we apply an exact power spectrum estimation algorithm to submaps of the data at various resolutions, and then combine the results in an optimal manner. To analyze larger maps efficiently one must resort to suboptimal combinations in which cross-map power spectrum error correlations are only calculated approximately. We expect such approximations to work well in general, and in particular for the megapixel maps to come from the next generation of satellite missions.

CMB and Inflation: the report from Snowmass 2001

Abstract: Accelerator–based efforts spanning decades have revealed no direct evidence of physics beyond the Standard Model. Although this is likely to change with the Large Hadron Collider (LHC) or possibly even with the current (higher–luminosity) run at the Tevatron, we point out that astrophysical evidence for physics beyond the standard model has already grown to be conclusive. Observations indicate the need for • inflation, • dark energy, • dark matter, and • massive neutrinos. In short, cosmology is delivering on its promise of probing fundamental physics. These results are creating intellectual excitement in the high energy physics community. They also signal an opportunity. The prospects are bright for further progress in our understanding of fundamental physics, via cosmology, and researchers trained in particle physics should not only be interested, but are well–equipped to contribute. Indeed, a number of particle physicists have become actively engaged in astrophysical observations. In this report we review the current status of observations of the temperature of the cosmic microwave background (CMB), and explain how they provide evidence of an inflationary era of expansion in the early Universe and the existence of “dark energy”. One of our intentions in providing this review is to demonstrate that cosmology has a track record which suggests that we have some understanding of the system we are studying. This track record bolsters the case that we will be able to get meaningful answers to the more detailed questions that are motivating planned observations. These future observations, which we discuss, include more detailed measurement of temperature maps, detection and measurement of polarization (including the modes generated by gravitational waves) and Sunyaev–Zeldovich surveys. Of course, observational cosmology is much broader than the topics we are covering, and the interested reader is encouraged to consult the other P4 and E6 subtopic reports.