The Cosmic Microwave Background Anisotropy Power Spectrum measured by Archeops

TL;DR

Archeops measures the CMB angular power spectrum in 16 bins for $\ell$ in [15,350], using a balloon-borne, Planck-like telescope and a two-photometer CMB channel. The analysis uses the MASTER method to derive an unbiased $C_\ell$ with corrections for beam, filtering, and pixelization, and includes extensive consistency tests and cross-validation against COBE/DMR and other experiments. The results reveal a prominent first acoustic peak around $\ell \approx 200$, with high signal-to-noise and broad sky coverage, establishing Archeops as a crucial precursor to Planck HFI. The work demonstrates the feasibility of large-sky, high-resolution CMB power-spectrum measurements from a short balloon flight and informs instrument design and analysis for future CMB missions.

Abstract

We present a determination by the Archeops experiment of the angular power spectrum of the cosmic microwave background anisotropy in 16 bins over the multipole range l=15-350. Archeops was conceived as a precursor of the Planck HFI instrument by using the same optical design and the same technology for the detectors and their cooling. Archeops is a balloon-borne instrument consisting of a 1.5 m aperture diameter telescope and an array of 21 photometers maintained at ~100 mK that are operating in 4 frequency bands centered at 143, 217, 353 and 545 GHz. The data were taken during the Arctic night of February 7, 2002 after the instrument was launched by CNES from Esrange base (Sweden). The entire data cover ~ 30% of the sky.This first analysis was obtained with a small subset of the dataset using the most sensitive photometer in each CMB band (143 and 217 GHz) and 12.6% of the sky at galactic latitudes above 30 degrees where the foreground contamination is measured to be negligible. The large sky coverage and medium resolution (better than 15 arcminutes) provide for the first time a high signal-to-noise ratio determination of the power spectrum over angular scales that include both the first acoustic peak and scales probed by COBE/DMR. With a binning of Delta(l)=7 to 25 the error bars are dominated by sample variance for l below 200. A companion paper details the cosmological implications.

Figures (4)

• Figure 1: Archeops CMB map (Galactic coordinates, centered on the Galactic anticenter, Northern hemisphere) in HEALPIX pixelisation (healpix) with 15 arcmin. pixels and a 15 arcmin. Gaussian smoothing. The map is a two--photometers coaddition. The dark blue region is not included in the present analysis because of possible contamination by dust. The colors in the map range from $-500$ to $500\ \mu\mathrm{K_{CMB}}$.
• Figure 2: The Archeops CMB power spectrum for the combination of the two photometers. Green and red data points correspond to two overlapping binnings and are therefore not independent. The light open diamonds show the null test resulting from the self difference (SD) of both photometers and the light open triangles correspond to the difference (D) of both photometers (shifted by $-2500\ \mu\mathrm{K}^2$ for clarity) as described in sect. \ref{['sect_selfdiff']} and shown in Tab. \ref{['tab:cl']}.
• Figure 3: Contamination by systematics : the Archeops CMB power spectrum statistical error bars (including noise and sample variance) are shown as the blue triangles. The large error bar in the first bin mainly comes from the high--pass filtering. A conservative upper--limit to contamination by dust and atmospheric signal is shown in red crosses, with a $\ell$ different binning to enhance the low $\ell$ side. Beam and time constants uncertainties are shown in dot--dashed blue and dashed green (see text). The 7% temperature calibration uncertainty is not shown here. The window functions are shown at the bottom of the figure.
• Figure 4: The Archeops power spectrum compared with results of COBE, Boomerang, Dasi, Maxima (tegmark, boom2, maxima2, dasi).