Arcminute Cosmology Bolometer Array Receiver

ACBAR Publications

High Resolution CMB Power Spectrum from the Complete ACBAR Data Set.
Reichardt, C. L.; Ade P. A. R.; Bock, J. J.; Bond, J. R.; Brevik, J. A.; Contaldi, C. R.; Daub, M. D.; Dempsey, J. T.; Goldstein, J. H.; Holzapfel, W. L.; Kuo, C. L.; Lange, A. E.; Lueker, M.; Newcomb, M.; Peterson, J. B.; Ruhl, J.; Runyan, M. C.; Staniszewski, Z.
Astrophysical Journal 694 (2009) 1200-1219

In this paper, we present results from the complete set of cosmic microwave background (CMB) radiation temperature anisotropy observations made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR) operating at 150 GHz. We include new data from the final 2005 observing season, expanding the number of detector-hours by 210% and the sky coverage by 490% over that used for the previous ACBAR release. As a result, the band-power uncertainties have been reduced by more than a factor of two on angular scales encompassing the third to fifth acoustic peaks as well as the damping tail of the CMB power spectrum. The calibration uncertainty has been reduced from 6% to 2.2% in temperature through a direct comparison of the CMB anisotropy measured by ACBAR with that of the dipole-calibrated WMAP3 experiment. The measured power spectrum is consistent with a spatially flat, ΛCDM cosmological model. We see evidence for weak gravitational lensing of the CMB at >3-sigma significance by comparing the likelihood for the best-fit lensed/unlensed models to the ACBAR+WMAP3 data. On fine angular scales, there is weak evidence (1.7 sigma) for excess power above the level expected from primary anisotropies. The source of this power cannot be constrained by the ACBAR 150 GHz observations alone; however, if it is the same signal seen at 30 GHz by the CBI and BIMA experiments, then it has a spectrum consistent with the Sunyaev-Zel'dovich effect.

Also available at astro-ph/0801.1491.

Improved Measurements of the CMB Power Spectrum with ACBAR
Kuo, C. L.; Ade P. A. R.; Bock, J. J.; Bond, J. R.; Contaldi, C. R.; Daub, M. D.; Goldstein, J. H.; Holzapfel, W. L.; Lange, A. E.; Lueker, M.; Newcomb, M.; Peterson, J. B.; Reichardt, C.; Ruhl, J.; Runyan, M. C.; Staniszewski, Z.
The Astrophysical Journal, Volume 664, Issue 2, pp. 687-701

We report improved measurements of temperature anisotropies in the cosmic microwave background (CMB) made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR). In this paper, we use a new analysis technique and include 30% more data from the 2001 and 2002 observing seasons than the first release (Kuo et al. 2004) to derive a new set of band-power measurements with significantly smaller uncertainties. The planet-based calibration used previously has been replaced by comparing the flux of RCW38 as measured by ACBAR and BOOMERANG to transfer the WMAP-based BOOMERANG calibration to ACBAR. The resulting power spectrum is consistent with the theoretical predictions for a spatially flat, dark energy dominated ΛCDM cosmology. Despite the exponential damping on small angular scales, the primary CMB fluctuations are detected with a signal-to-noise ratio of greater than 4 up to multipoles of l=2000. This increase in the precision of the fine-scale CMB power spectrum leads to only a modest decrease in the uncertainties on the parameters of the standard cosmological model. A joint analysis of the ACBAR results at 150 GHz and the CBI results at 30 GHz in the multipole range 2000 < l < 3000 shows that the measured power is consistent with the Sunyaev-Zel'dovich effect, but disfavors interpretations in which the excess power seen with CBI has a thermal spectrum. The results reported here are derived from a subset of the total ACBAR data set; the final ACBAR power spectrum at 150 GHz will include 3.7 times more effective integration time and 6.5 times more sky coverage than is used here.

Also available at astro-ph/0611198.

Millimeter Wavelength Brightness Fluctuations of the Atmosphere above the South Pole
Bussmann, R. S.; Holzapfel, W. L.; Kuo, C. L.
The Astrophysical Journal, Volume 622, Issue 2, pp. 1343-1355.

We report measurements of the millimeter wavelength brightness fluctuations produced by the atmosphere above the South Pole made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR). The data span the 2002 austral winter during which ACBAR was mounted on the Viper Telescope at the South Pole. We recover the atmospheric signal in the presence of instrument noise by calculating the correlation between signals from distinct elements of the ACBAR bolometer array. With this method, it is possible to measure atmospheric brightness fluctuations with a high signal-to-noise ratio even under the most stable atmospheric conditions. The observed atmospheric signal is characterized by the parameters of the Kolmogorov-Taylor (KT) model, which are the amplitude and power-law exponent describing the atmospheric power spectrum and the two components of the wind angular velocity at the time of the observation. The KT model is typically a good description of the observed fluctuations, and fits to the data produce values of the Kolmogorov exponent that are consistent with theoretical expectations. By combining the wind angular velocity results with measurements of the wind linear velocity, we find that the altitude of the observed atmospheric fluctuations is consistent with the distribution of water vapor determined from radiosonde data. For data corresponding to frequency passbands centered on 150, 219, and 274 GHz, we obtain median fluctuation power amplitudes of (10, 38, 74) mK2 rad-5/3 in Rayleigh-Jeans temperature units. Comparing with previous work, we find that these median amplitudes are approximately an order of magnitude smaller than those found at the South Pole during the austral summer and at least 30 times lower than found at the ALMA site in the Atacama desert.

Also available at astro-ph/0412031.

We review the first science results from the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a multi-frequency millimeter-wave receiver optimized for observations of the Cosmic Microwave Background (CMB) and the Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies. ACBAR was installed on the 2 m Viper telescope at the South Pole in January 2001 and the results presented here incorporate data through July 2002. We present the power spectrum of the CMB at 150 GHz over the range l=150-3000 measured by ACBAR as well as estimates for the values of the cosmological parameters within the context of LambdaCDM models. We find that the inclusion of OmegaLambda greatly improves the fit to the power spectrum. We also observe a slight excess of small-scale anisotropy at 150 GHz; if interpreted as power from the SZ effect of unresolved clusters, the measured signal is consistent with CBI and BIMA within the context of the SZ power spectrum models tested.

Also available at astro-ph/0305553.

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 150 GHz band map, we reached an RMS of 8.0 uK 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 $\Delta \ell=150$. 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 $\Lambda$CDM Universe.

Also available at astro-ph/0212289.

We report an investigation of cosmological parameters based on the measurements of anisotropy in the cosmic microwave background radiation (CMB) made by ACBAR. We use the ACBAR data in concert with other recent CMB measurements to derive Bayesian estimates of parameters in inflation-motivated adiabatic cold dark matter models. We apply a series of additional cosmological constraints on the shape and amplitude of the density power spectrum, the Hubble parameter and from supernovae to further refine our parameter estimates. Previous estimates of parameters are confirmed, with sensitive measurements of the power spectrum now ranging from \ell \sim 3 to 2800. Comparing individual best model fits, we find that the addition of \Omega_\Lambda as a parameter dramatically improves the fits. We also use the high-\ell data of ACBAR, along with similar data from CBI and BIMA, to investigate potential secondary anisotropies from the Sunyaev-Zeldovich effect. We show that the results from the three experiments are consistent under this interpretation, and use the data, combined and individually, to estimate \sigma_8 from the Sunyaev-Zeldovich component.

Also availible at: astro-ph/0212517

We describe the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a multifrequency millimeter-wave receiver designed for observations of the Cosmic Microwave Background (CMB) and the Sunyaev-Zel'dovich effect in clusters of galaxies. The ACBAR focal plane consists of a 16-pixel, background-limited, 240 mK bolometer array that can be configured to observe simultaneously at 150, 220, 280, and 350 GHz. With 4-5' FWHM Gaussian beam sizes and a 3 degree azimuth chop, ACBAR is sensitive to a wide range of angular scales. ACBAR was installed on the 2 m Viper telescope at the South Pole in January 2001. We describe the design of the instrument and its performance during the 2001 and 2002 observing seasons.

Also availible at: astro-ph/0303515