Richard Gispert passed away few weeks after his return from the early mission to Trapani. Abstract. We present the first determination of the Galactic polarized emission at 353 GHz by Archeops. The data were taken during the Arctic night of February 7, 2002 after the balloon-borne instrument was launched by CNES from the Swedish Esrange base near Kiruna. In addition to the 143 GHz and 217 GHz frequency bands dedicated to CMB studies, Archeops had one 545 GHz and six 353 GHz bolometers mounted in three polarization-sensitive pairs that were used for Galactic foreground studies. We present maps of the I, Q, U Stokes parameters over 17% of the sky and with a 13 arcmin resolution at 353 GHz (850 µm). They show a significant Galactic large scale polarized emission coherent on the longitude ranges [100, 120] and [180, 200] deg. with a degree of polarization at the level of 4-5%, in agreement with expectations from starlight polarization measurements. Some regions in the Galactic plane (Gem OB1, Cassiopeia) show an even stronger degree of polarization in the range 10-20%. These findings provide strong evidence for a powerful grain alignment mechanism throughout the interstellar medium and a coherent magnetic field coplanar to the Galactic plane. This magnetic field pervades even some dense clouds. Extrapolated to high Galactic latitude, these results indicate that interstellar dust polarized emission is the major foreground for PLANCK-HFI CMB polarization measurements.

Abstract. We analyze the cosmological constraints that Archeops (Benoît et al. 2003) places on adiabatic cold dark matter models with passive power-law initial fluctuations. Because its angular power spectrum has small bins in and large coverage down to COBE scales, Archeops provides a precise determination of the first acoustic peak in terms of position at multipole l peak = 220 ± 6, height and width. An analysis of Archeops data in combination with other CMB datasets constrains the baryon content of the Universe, Ω b h 2 = 0.022−0.004 , compatible with Big-Bang nucleosynthesis and with a similar accuracy. Using cosmological priors obtained from recent non-CMB data leads to yet tighter constraints on the total density, e.g. Ω tot = 1.00 +0.03 −0.02 using the HST determination of the Hubble constant. An excellent absolute calibration consistency is found between Archeops and other CMB experiments, as well as with the previously quoted best fit model. The spectral index n is measured to be 1.04 +0.10 −0.12 when the optical depth to reionization, τ, is allowed to vary as a free parameter, and 0.96 +0.03 −0.04 when τ is fixed to zero, both in good agreement with inflation.Key words. cosmic microwave background -cosmological parameters -early Universe -large-scale structure of the Universe Send offprint requests to: A. Benoît,

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 = 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 arcmin) 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 ∆ = 7 to 25 the error bars are dominated by sample variance for below 200. A companion paper details the cosmological implications.

Aims. Archeops is a balloon-borne experiment inspired by the Planck satellite and its high frequency instrument (HFI). It is designed to measure the cosmic microwave background (CMB) temperature anisotropies at high angular resolution (∼12 arcmin) over a large fraction of the sky (around 30%) at 143, 217, 353, and 545 GHz. The Archeops 353 GHz channel consists of three pairs of polarized sensitive bolometers designed to detect the polarized diffuse emission of Galactic dust. Methods. In this paper we present an update of the instrumental setup, as well as the flight performance for the last Archeops flight campaign (February 2002 from Kiruna, Sweden). We also describe the processing and analysis of the Archeops time-ordered data for that campaign, which led to measurement of the CMB anisotropy power spectrum in the multipole range = 10-700 and to the first measurements of both the polarized emission of dust at large angular scales and its power spectra in the multipole range = 3-70 Results. We present maps covering approximately 30% of the sky. These maps contain Galactic emission, including the Galactic plane, in the four Archeops channels at 143, 217, 353, and 545 GHz and CMB anisotropies at 143 and 217 GHz. These are one of the first sub-degree-resolution maps in the millimeter and submillimeter ranges of the large angular-scale diffuse Galactic dust emission and CMB temperature anisotropies, respectively.Key words. methods: data analysis -cosmic microwave background IntroductionThe measurement of the cosmic microwave background (CMB) anisotropies in temperature and polarization is a fundamental test of our concepts of modern cosmology and of the physics of the early Universe. Since the first detection of CMB anisotropies by the COBE satellite in 1992 (Smoot et al. 1992), a large number of ground-based and balloon-borne experiments, such as DASI (Halverson et al. 2002), CBI (Mason et al. 2003), VSA (Dickinson et al. 2004), BOOMERanG (Netterfield et al. 2002 and Maxima (Hanany et al. 2000), have measured the CMB angular power spectra from a few-degrees down to subdegree scales. However, simultaneous observation of very large and small angular scales have proved to be particularly difficult, as it requires both large sky coverage and high angular resolution. This was first achieved by this experiment, Archeops (Benoît et al. 2003a;Tristram et al. 2005b), which measured the CMB power spectrum in the multipole range 10 < < 700. Since, the WMAP satellite mission has detected the CMB anisotropies, both in temperature and polarization.Richard Gispert passed away few weeks after his return from the early mission to Trapani.Archeops, described in detail in Benoît et al. (2002), is a balloon-borne experiment designed as a testbed for many of the technologies to be used on the high frequency instrument (HFI) of the Planck satellite. Its telescope and focal plane optics are widely inspired by the Planck design. Implementation of the measurement chains -cryogenics, optics, bolometers, readout electronics -valida...

No abstract