A Measurement of the Angular Power Spectrum of the CMB Temperature Anisotropy from the 2003 Flight of Boomerang

TL;DR

This paper reports a high-precision measurement of the CMB temperature angular power spectrum using Boomerang 2003’s polarization-sensitive bolometers. The authors implement two independent analysis pipelines and a Monte Carlo-based estimator to derive the TT spectrum across 50 < l < 1500, while carefully propagating calibration, beam, and foreground uncertainties. The resulting spectrum exhibits acoustic peaks and damping consistent with ΛCDM and is in good agreement with B98 and WMAP, providing a key link between all-sky and high-l measurements. The work also demonstrates robust foreground control and delivers publicly accessible power-spectrum data products for broader community use.

Abstract

We report on observations of the Cosmic Microwave Background (CMB) obtained during the January 2003 flight of Boomerang . These results are derived from 195 hours of observation with four 145 GHz Polarization Sensitive Bolometer (PSB) pairs, identical in design to the four 143 GHz Planck HFI polarized pixels. The data include 75 hours of observations distributed over 1.84% of the sky with an additional 120 hours concentrated on the central portion of the field, itself representing 0.22% of the full sky. From these data we derive an estimate of the angular power spectrum of temperature fluctuations of the CMB in 24 bands over the multipole range (50 < l < 1500). A series of features, consistent with those expected from acoustic oscillations in the primordial photon-baryon fluid, are clearly evident in the power spectrum, as is the exponential damping of power on scales smaller than the photon mean free path at the epoch of last scattering (l > 900). As a consistency check, the collaboration has performed two fully independent analyses of the time ordered data, which are found to be in excellent agreement.

Figures (7)

• Figure 1: The left and right panels show the sky coverage obtained during the January 2003 flight of Boomerang. The integration times per $3.4^\prime$ pixel are shown for the shallow and deep data subsets described in the text. Galactic latitude contours of $b=\{-30,-20\}$ are shown for reference. Approximately 75 hours of observation are devoted to the shallow region, with an additional 120 hours concentrated in the central deep field. The cross-linking of the scans due to sky rotation is evident in the diagonal striping of the coverage, which has a $\approx 20^\circ$ opening angle. Known extragalactic point sources, shown masked in these plots, are excluded from the analysis.
• Figure 2: In the top panel, we show a comparison of the temperature angular power spectrum derived from the B03 data using the NA pipeline (xFaster, in red circles) and the IT pipeline, the latter using both uniform (green stars) and noise weighted (blue squares) masks. For the IT results, uniform weighting of the combined shallow and deep data results in nearly optimal errorbars in the signal-dominated regime, while the $1/\sqrt{N_{obs}}$ pixel weighting is required to achieve this sensitivity in the noise dominated regime. The NA spectrum is derived using a hybrid auto- and cross- correlation technique which achieves nearly optimal errors across the full multipole range. In the lower panel, a comparison of the angular power spectrum derived from the B98 data [retal], and the B03 results reported here. The 2003 coverage is a sub-set of the region observed in 1998, so the signal is completely correlated between the two datasets. The binning of the B03 data in the lower panel is shifted by half of a bin relative to the top panel.
• Figure 3: The temperature angular power spectrum, $\mathcal{C}_\ell^{\hbox{\tiny TT}}$, derived from the B03 data. The red points represent an alternate binning, and should not be interpreted as having statistical weight beyond that of the nominally binned data, which are shown with errorbars. The anti-correlations between neighboring bands range from the twelve to twenty percent level. The envelope of the beam uncertainty is indicated by ticks bracketing the one sigma errorbars for each of the bandpower estimates. As discussed in Section \ref{['sec:sys']}, these limits indicate the amount of "tilt" to the spectrum that is allowed by the beam uncertainty, and should not be interpreted as an additional uncorrelated error in each bin. The solid green line is the concordance $\Lambda$CDM model which best fits all published CMB data, including the B03 temperature and polarization results. The power spectra of the consistency checks described in the text are shown in the lower two panels.
• Figure 4: The propagation of instrumental calibration errors to the bandpower estimates. The amplitude of the statistical uncertainties (sample variance plus instrumental noise) for each bin are shown with circles. The contributions from the relative calibration, $s \pm0.8$%, the the in-flight transfer function $\tau \pm 10\%$, the polarization angle, $\psi \pm 2^\circ$, and polarization efficiency $\epsilon \pm 3\%$ are shown for reference. The horizontal ticks indicate the effect of beam uncertainty. Note that each of these effects are highly correlated between bins, and therefore are not properly treated by quadrature addition to the statistical uncertainty in a given bin. Since the correlation structure of these errors is known, they are more properly treated as nuisance parameters, and as such are marginalized over during the cosmological parameter estimation [bridle02]. For the B03 parameter extraction, only the beam error and calibration uncertainty are treated in this manner [b2k_params].
• Figure 5: A comparison of recently published cmb power spectra, $\mathcal{C}_\ell^{\hbox{\tiny TT}}$, [the data shown are from wmap_hinshawacbar_spectracbi_mosaic, in addition to B03]. The data shown are derived from independent measurements that span two orders of magnitude in electromagnetic frequency (20-200 GHz), employ both single dish and interferometric instruments, and operate from terrestrial, balloon-borne, and orbital platforms. The remarkable degree of accord between such a diverse set of measurements is indicative of the maturity of the observational field.