High Resolution Observations of the CMB Power Spectrum with ACBAR

Abstract

We report the first measurements of anisotropy in the cosmic microwave background (CMB) radiation with the Arcminute Cosmology Bolometer Array Receiver (ACBAR). The instrument was installed on the 2.1m Viper telescope at the South Pole in January 2001; the data presented here are the product of observations up to and including July 2002. The two deep fields presented here, have had offsets removed by subtracting lead and trail observations and cover approximately 24 deg^2 of sky selected for low dust contrast. These results represent the highest signal to noise observations of CMB anisotropy to date; in the deepest 150GHz band map, we reached an RMS of 8.0μK per 5' beam. The 3 degree extent of the maps, and small beamsize of the experiment allow the measurement of the CMB anisotropy power spectrum over the range \ell = 150-3000 with resolution of Δ\ell=150. The contributions of galactic dust and radio sources to the observed anisotropy are negligible and are removed in the analysis. The resulting power spectrum is found to be consistent with the primary anisotropy expected in a concordance ΛCDM Universe.

Figures (11)

• Figure 1: The beams of the $150\,$GHz array elements determined from observations of the CMB2 guiding quasar in the 2001 season. These images represent an average over the entire observation period and include any distortions due to changes in pointing or beamsize.
• Figure 2: The beams of the $150\,$GHz array elements determined from observations of the guiding quasar in the CMB5 field. These images represent an average over the entire observation period and include any distortions due to changes in pointing or beamsize.
• Figure 3: The window functions ($W_{B\ell}/\ell$) for the decorrelated Acbar band powers. The vertical lines show the band boundaries. Numerical tabulations of these functions are given on the Acbar website.
• Figure 4: The results of 300 Monte Carlo runs using the measured Acbar noise correlation. The solid line is the input fiducial $\Lambda$CDM model. It is clear that the analysis method accurately reproduces the input power spectrum.
• Figure 5: The top panel shows the LMT differenced, atmospheric mode removed, noise weighted, coadded map for the CMB2 field. The guide quasar and radio source Pictor-A have been replace with black pixels. The small white circle in the lower left hand corner of the map represents the FWHM of the average array element beamsize as determined from the coadded quasar image. The predominance of extended structure in the vertical direction is because the extended horizontal structure has been projected out in the atmospheric mode removal. The lower panel shows the noise in the LMT difference map as a function of position.