DASI First Results: A Measurement of the Cosmic Microwave Background Angular Power Spectrum

TL;DR

The paper reports the first-season DASI measurements of the CMB angular power spectrum in the range $100 < \ell < 900$, obtained with a 13-element interferometer at the South Pole. It introduces a maximum-likelihood framework with constraint matrices to marginalize ground signals and point sources, and tests for correlations with diffuse foreground templates. The analysis yields a clear first acoustic peak near $\ell \approx 200$ and a second peak near $\ell \approx 550$, with hints of a third around $\ell \approx 800$, consistent with adiabatic inflationary models and supporting the presence of dark matter. The work demonstrates low diffuse foreground contamination and provides high-precision band powers to constrain cosmological parameters in a subsequent paper, Pryke et al. 2001.

Abstract

We present measurements of anisotropy in the Cosmic Microwave Background (CMB) from the first season of observations with the Degree Angular Scale Interferometer (DASI). The instrument was deployed at the South Pole in the austral summer 1999--2000, and made observations throughout the following austral winter. We have measured the angular power spectrum of the CMB in the range 100<l<900 with high signal-to-noise. In this paper we review the formalism used in the analysis, in particular the use of constraint matrices to project out contaminants such as ground and point source signals, and to test for correlations with diffuse foreground templates. We find no evidence of foregrounds other than point sources in the data, and find a maximum likelihood temperature spectral index beta = -0.1 +/- 0.2 (1 sigma), consistent with CMB. We detect a first peak in the power spectrum at l approx 200, in agreement with previous experiments. In addition, we detect a peak in the power spectrum at l approx 550 and power of similar magnitude at l approx 800 which are consistent with the second and third harmonic peaks predicted by adiabatic inflationary cosmological models.

Figures (1)

• Figure 1: The angular power spectrum from the first season of DASI observations, plotted in nine bands (filled circles). We have analyzed the same data in nine bands shifted to the right (open circles). The alternate set of band powers are shown to demonstrate the robustness of the likelihood analysis procedure. To extract cosmological parameters (Paper III), only the nine bands shown in the primary analysis (filled circles) are used. Adjacent bands are anticorrelated at the 20% level (see Table \ref{['tab:corr']}). In addition to the uncertainties plotted above, there is a calibration uncertainty of 8%, expressed as a fractional uncertainty on the $C_l$ band powers (4% in $\Delta T/T$), which is completely correlated across all bands due to the combined flux scale and beam uncertainties.