Cosmological Results from Five Years of 30 GHz CMB Intensity Measurements with the Cosmic Background Imager

Abstract

We present final results on the angular power spectrum of total intensity anisotropies in the CMB from the CBI. Our analysis includes all primordial anisotropy data collected between January 2000 and April 2005, and benefits significantly from an improved maximum likelihood analysis pipeline. It also includes results from a 30 GHz foreground survey conducted with the Green Bank Telescope (GBT) which places significant constraints on the possible contamination due to foreground point sources. We improve on previous CBI results by about a factor of two in the damping tail. These data confirm, at ~3-sigma, the existence of an excess of power over intrinsic CMB anisotropy on small angular scales (l > 1800). Using the GBT survey, we find currently known radio source populations are not capable of generating the power; a new population of faint sources with steeply rising spectral indices would be required to explain the excess with sources... We also present a full cosmological parameter analysis of the new CBI power spectrum... With CBI alone, the full parameter analysis finds the excess is 1.6-sigma above the level expected for a sigma_8=0.8 universe. We find the addition of high-l CMB data substantially improves constraints on cosmic string contributions to the TT power spectrum as well as the running of the scalar spectral index... We also present forecasts for what other experiments should see at different frequencies and angular resolutions given the excess power observed by CBI. We find that the reported high-l bandpowers from current high resolution CMB bolometer experiments are consistent with each other and CBI if the excess power is due to the SZE at the CBI-level of 2.5 +/- 1 times the sigma_8=0.8 standard SZ template. <Abridged>

Figures (9)

• Figure 1: Effects of projections on the expected spectrum from the CBI strips. The red triangles show the expected spectrum from just the TT part of the CBI polarization data with no removal of ground or sources. The green squares show the expected spectrum when the scan mean (which contains the ground signal) is projected out. The red X's show the spectrum when only the sources are projected. The green X's show the spectrum when both sources and ground are projected - there is a significant bias downwards in the spectrum. The grey circles show the the same spectrum when the scan mean is subtracted rather than projected, and the sources are projected using the numerically stable method of Appendix \ref{['sec:maxlike']}. The black curve is the input CMB spectrum. This method keeps the covariance matrix better conditioned, so it is less susceptible to roundoff errors in the inversion. These spectra are fit to the theoretical CMB+noise signal matrix using the techniques described in Appendix \ref{['sec:spec_expected']}, which is equivalent to averaging over all possible noise and signal simulations. The CBI differenced data from paper7 were already effectively scan-mean subtracted, and so are not included here.
• Figure 2: CBI total intensity power spectrum. The blue points are the CBI power spectrum in this work, given in text form in Table \ref{['tbl:powspec']}. The salmon points are the WMAP 5-year spectrum Nolta08. The green points are the QUaD 2-year spectrum quad08. The burnt sienna points are the ACBAR 150 GHz spectrum acbar08. The full CBI spectrum, including bin correlations and window functions, is available online.
• Figure 3: A comparison of the CBI 5-year power spectrum, including results from the GBT 30 GHz survey, with the two-year CBI power spectrum of paper7. Note the changed finer binning at high $\ell$ for the power spectrum from the 5-year data. The window function of the paper7 highest-$\ell$ bin extends from $\ell \sim 2000$ to $\ell \sim 3500$. Note that the error bar on that very big bin is about the same as for the last of the finer bins, in spite of the large paper7 bin being broken up into three distinct bins in this work. The main reasons for the improvement in the spectrum is the factor of two more data, and the development of analysis techniques that allowed us to combine these disparate datasets. In the damping tail, the new spectrum is about a factor of two improvement over paper7.
• Figure 4: The CBI, ACBAR, QUaD, and BIMA power spectra at small angular scales are contrasted. The solid black line shows the tilted $\Lambda$CDM model from Section \ref{['subsec:powerspectrum']} for the CMB primary anisotropies. The dashed lines include the contribution of secondary SZ anisotropy using the model of komatsuandseljak with the best-fit template scaling of $3.5$ (in bandpower) that we have determined using only the CBI data. The SZ plus primary anisotropy power combination at 30 GHz is the blue-dashed line. Note that, apart from fitting the CBI power spectrum, it passes through the BIMA point at $\ell \sim 5300$dawson06. We have also forecast the level for SZ plus primary anisotropies at 150 GHz (red dashed line) and 100 GHz (orange dot-dash line). These are compared with the power spectra of ACBAR acbar08and QUaD quad08.
• Figure 5: A comparison of the power spectrum obtained from all CBI TT data with that obtained when the deep fields are excluded, and with that obtained when only the deep fields are used. Although the error for the no-deeps at $\ell \sim 2500$ is larger, and consistent with no excess at the $\sim 1-\sigma$ level, the overall mean amplitude is about the same as for the deep-only case. The all-data and no-deeps spectra are at the same $\ell$, but have been offset for clarity.