Power Spectrum of the Cosmic Microwave Background

from HEMT receivers

Tim Pearson

2004 Jan 1

The fluctuations in intensity of the cosmic microwave background are due to sound waves in the early universe created as the hot plasma oscillates under the force of gravity created by the dark matter. Over the last few years the angular power spectrum has been measured with high precision using many instruments on satellites, on balloons, and on the ground. The power spectrum is plotted versus multipole number l, with larger l corresponding to smaller angular scales. The WMAP results, published in 2003, have defined the spectrum on the largest angular scales (low l) with accuracy limited by cosmic variance. They are supplemented by results at smaller scales from four ground-based interferometers: DASI at the South Pole, VSA in Tenerife, Caltech's Cosmic Background Imager (CBI) in Chile, and BIMA in California. The CBI and BIMA results show tantalizing evidence for excess power above the predictions of "concordance" Lambda-CDM models (black curve) that fit the WMAP and other data very well. The excess could be due to scattering of the CMB radiation by the Sunyaev-Zeldovich effect associated with early stars or clusters of galaxies.

All the results presented in this figure are based on observations made with High Electron Mobility Transistor (HEMT) amplifiers produced in the National Radio Astronomy Observatory's Central Development Laboratory. They are in good agreement with results from incoherent bolometer detectors (including Boomerang, Maxima, and Acbar).