A Measurement of the Cosmic Microwave Background Angular Power Spectrum with DASI

Abstract

The Cosmic Microwave Background (CMB) has long been recognized as an astounding source of information about the early Universe. In this thesis we describe the design, implementation, and first-year results of the Degree Angular Scale Interferometer (DASI), a compact interferometer designed to measure the angular power spectrum of the CMB. We discuss details of the optics, receivers, and power spectrum analysis, including the use of constraint matrices to project out contaminants and test for correlations with diffuse foreground templates. We present a measurement of the CMB angular power spectrum in the multipole range l ≈ 100- 900 in nine bands. The measured fluctuations have a temperature spectral index of β = -0.1 ± 0.2 (1σ) consistent with CMB. We find no evidence of foregrounds other than point sources in the data. We detect a first peak in the power spectrum at l ~ 200, a second peak in the power spectrum at l ~ 550, and a rise in the power spectrum at l ~ 800 which is indicative of a third, consistent with inflationary theories. Using the DASI measurement along with COBE DMR data, and adopting conservative priors on the Hubble parameter h > 0.45 and an optical depth due to reionization 0.0 ≤ τ_c ≤ 0.4, we constrain the total density of the Universe Ω_(tot) = 1.04 ± 0.06, the spectral index of the primordial density fluctuations n_s = 1.01^(+0.08)_(-0.06), and the physical baryon density Ω_bh^2 = 0.022^(+0.004)_(-0.003) among others (all 68% confidence limits). These constraints are consistent with inflation and estimates of Ω_bh^2 from Big Bang Nucleosynthesis. With prior h = 0.72 ± 0.08, we constrain the matter density Ω_m = 0.40 ± 0.15, and the vacuum energy density Ω_Λ = 0.60 ± 0.15, indicating from CMB data the presence of dark matter and dark energy in the Universe.