Improved Measurements of the CMB Power Spectrum with ACBAR

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Abstract

We report improved measurements of temperature anisotropies in the cosmic\nmicrowave background (CMB) radiation made with the Arcminute Cosmology\nBolometer Array Receiver (ACBAR). In this paper, we use a new analysis\ntechnique and include 30% more data from the 2001 and 2002 observing seasons\nthan the first release to derive a new set of band-power measurements with\nsignificantly smaller uncertainties. The planet-based calibration used\npreviously has been replaced by comparing the flux of RCW38 as measured by\nACBAR and BOOMERANG to transfer the WMAP-based BOOMERANG calibration to ACBAR.\nThe resulting power spectrum is consistent with the theoretical predictions for\na spatially flat, dark energy dominated LCDM cosmology including the effects of\ngravitational lensing. Despite the exponential damping on small angular scales,\nthe primary CMB fluctuations are detected with a signal-to-noise ratio of\ngreater than 4 up to multipoles of l=2000. This increase in the precision of\nthe fine-scale CMB power spectrum leads to only a modest decrease in the\nuncertainties on the parameters of the standard cosmological model. At high\nangular resolution, secondary anisotropies are predicted to be a significant\ncontribution to the measured anisotropy. A joint analysis of the ACBAR results\nat 150 GHz and the CBI results at 30 GHz in the multipole range 2000 < l < 3000\nshows that the power, reported by CBI in excess of the predicted primary\nanisotropy, has a frequency spectrum consistent with the thermal\nSunyaev-Zel'dovich effect and inconsistent with primary CMB. The results\nreported here are derived from a subset of the total ACBAR data set; the final\nACBAR power spectrum at 150 GHz will include 3.7 times more effective\nintegration time and 6.5 times more sky coverage than is used here.

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