High resolution CMB power spectrum from the complete ACBAR data set

TL;DR

The study delivers a comprehensive high-resolution CMB power spectrum from the complete ACBAR data set at 150 GHz, extending coverage to the damping tail and the fourth–fifth acoustic peaks. By cross-calibrating with WMAP5 and incorporating weak lensing, the analysis yields precise cosmological parameters consistent with a flat ΛCDM universe, with σ8 ≈ 0.80 and Ωm ≈ 0.26. There is a modest high-ℓ excess that could arise from the Sunyaev-Zel'dovich effect or dusty/dusty proto-galaxies, but the CBI excess at 30 GHz is unlikely to have a primordial origin; foreground marginalization has little impact on the primary parameter inferences. Overall, the results reinforce the standard cosmological model, demonstrate the importance of lensing in CMB analyses, and provide tight constraints on secondary contributions, including SZ and point sources.

Abstract

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 2.1% in temperature through a direct comparison of the CMB anisotropy measured by ACBAR with that of the dipole-calibrated WMAP5 experiment. The measured power spectrum is consistent with a spatially flat, LambdaCDM cosmological model. We include the effects of weak lensing in the power spectrum model computations and find that this significantly improves the fits of the models to the combined ACBAR+WMAP5 power spectrum. The preferred strength of the lensing is consistent with theoretical expectations. On fine angular scales, there is weak evidence (1.1 sigma) for excess power above the level expected from primary anisotropies. We expect any excess power to be dominated by the combination of emission from dusty protogalaxies and the Sunyaev-Zel'dovich effect (SZE). However, the excess observed by ACBAR is significantly smaller than the excess power at ell > 2000 reported by the CBI experiment operating at 30 GHz. Therefore, while it is unlikely that the CBI excess has a primordial origin; the combined ACBAR and CBI results are consistent with the source of the CBI excess being either the SZE or radio source contamination.

Figures (14)

• Figure 1: The ACBAR fields overlaid on the IRAS dust map. The position of each field is plotted and labeled with the field name. The color coding indicates the year in which the observations occurred: red $\equiv$ 2001, orange $\equiv$ 2002, and yellow $\equiv$ 2005. The bulk of the 2005 season was targeted at large, comparatively shallow fields, increasing the total sky coverage by a factor of six. The fields are plotted on top of the 100 $\mu$m IRAS dust map schlegel98. Each field lies within the "Southern hole", a region of low dust emission visible from the South Pole. The CMB8 field (lower right corner) was targeted at the deep region of the B03 experiment as an alternative calibration path to the WMAP cross-calibration used for the results presented here.
• Figure 2: ACBAR Beam Uncertainty and Beam Function. Solid line & left axis: The 1$\sigma$ envelope for uncertainty in the ACBAR beam function $B_\ell$. The increasing uncertainty above $\ell=1000$ reflects the 2.6% uncertainty in the fitted Gaussian FWHMs. The behavior at $\ell<1000$ is a combination of the uncertainty in the measured sidelobes and the calibration method 'pinning' the transfer function for $\ell \in [256,512]$. Dashed line & right axis: The measured ACBAR beam function.
• Figure 3: Systematic tests performed on the ACBAR data. Top: Power spectrum ( red triangle) for differenced maps from the first half of the season and second half of the season for each field, compared to the results of Monte Carlo simulations ( error bars). Middle: Power spectrum ( blue star) derived from difference maps of the left- and right-going chopper sweeps for all ten fields. Bottom: The undifferenced band-powers from Table \ref{['tab:bands']} ( black diamonds) compared to both jackknife power spectra: the left-right jackknife ( blue star) and first half-second half jackknife ( red triangle).
• Figure 4: Dust emission is not detected in the ACBAR fields. Parameterizing the dust signal as $T_{CMB}+\xi T_{FDS}$, a suite of Monte Carlo realizations of maps of CMB and noise is used to estimate the uncertainty in $\xi$. We find the upper limits in each field to be consistent with the FDS99 model ($\xi = 1$), but the data somewhat favor a lower dust amplitude. The reduced $\chi^2$ of the measured amplitudes $\xi$s is 0.75 under the assumption that $\langle \xi \rangle = 0$ (the dashed line). The reduced $\chi^2$ for the FDS99 model with $\langle \xi \rangle = 1$ is 1.12 (the dotted line).
• Figure 5: The decorrelated ACBAR band-powers for the full data set. The $1\sigma$ error bars are derived from the offset-lognormal fits to the likelihood function. The band-powers are in excellent agreement with a $\Lambda$CDM model. The damping of the anisotropies is clearly seen with a S/N $>$ 4 out to $\ell=2500$. The third acoustic peak (at $\ell \sim 800$), fourth acoustic peak (at $\ell \sim 1100$), and fifth acoustic peak (at $\ell \sim 1400$) are visible. The plotted lines are the best fits to the ACBAR and WMAP5 band-powers for a spatially flat, $\Lambda$CDM universe with no SZE contribution. A lensed ( red) and unlensed ( blue) model spectrum is shown for a fixed parameter set; the lensed spectrum is a significantly better fit to the ACBAR data.