Direct measurement of the angular power spectrum of cosmic microwave background temperature anisotropies in the WMAP Data
Date Issued
2011
Date
2011
Author(s)
Chen, Fei-Fan
Abstract
Roughly 400,000 years after the Big Bang, electrons and protons combined to form neutral hydrogen, an event usually known as recombination. At that time, cosmic microwave background photons interact very weakly with neutral hydrogen and therefore CMB photons started to move through the early universe, which makes our universe visible. Thus, by studying the detailed physical properties of the radiation, we can learn about conditions in the universe at very early times. The CMB angular power spectrum is a useful tool that makes it possible for us to study the composition and history of our early universe, as well as the processes that seeded the fluctuations. The physics behind the angular power spectrum manifest itself in the location and height of these acoustic peaks and hence its precise measurement is one of the crucial tasks in CMB studies. Traditionally estimating CMB angular power spectrum needs to use Galactic foreground templates or ILC method to avoid foreground emission, which would thus break the orthogonality in the spherical harmonic analysis and also makes the process complex. We thus propose another method without masking foreground contamination emission. First we introduce flat-sky approximation and cross power spectrum (XPS). For flat-sky approximation, we find its scaling relation precise and XPS has the ability to eliminate the uncorrelated signal while preserve the correlated one. Thus based on flat-sky approximation and XPS, we can estimate the window function of WMAP differential assemblies maps from bright point sources by calculating XPS of two square patches of sky where there is a bright point source in the center. We demonstrate that retrieving window function of WMAP Difference Assembly maps from bright extragalactic point sources is useful and we further apply it to extract the unknown window function of WMAP frequency band maps. We are also the first team to extract window functions of the WMAP frequency band maps. In order to reach CMB angular power spectrum, we need to deal with three parts independently, which are foreground contamination, noise and the window functions. The foreground contamination is mainly composed of synchrotron, free-free, and dust emission, which can be solved by choosing low-variance patches. The instrument noise can be eliminated by calculating the XPS from the same patches of the V and W band . It is then deconvolved by the window function of the V and W frequency band map. Our simple method can yields the CMB power spectrum a clear 2nd Doppler peak and the 3rd peak is visible. The first part of our thesis, "Cross-Power Spectrum and Its Application on Window Functions in the WMAP Data", will be published in the Astrophysical Journal in August 20, 2011, V737 -2 and the second part, "Direct measurement of the angular power spectrum of cosmic microwave background temperature anisotropies in the WMAP Data", is about to be submitted.
Subjects
cosmology
cosmic microwave background
data analysis
observation
Type
thesis
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