We present the first sky maps from the BEAST (Background Emission Anisotropy Scanning Telescope) experiment. BEAST consists of a 2.2 m off-axis Gregorian telescope fed by a cryogenic millimeter wavelength focal plane currently consisting of six Q band (40 GHz) and two Ka band (30 GHz) scalar feed horns feeding cryogenic HEMT amplifiers. Data were collected from two balloon-borne flights in 2000, followed by a lengthy ground observing campaign from the 3.8 km altitude University of California White Mountain Research Station. This paper reports the initial results from the ground-based observations. The instrument produced an annular map covering the sky over 33 degrees < delta < 42 degrees. The maps cover an area of 2470 deg(2) with an effective resolution of 23' FWHM at 40 GHz and 30' at 30 GHz. The map rms (smoothed to 300 and excluding Galactic foregrounds) is 57 +/- 5 mu K (Rayleigh-Jeans) at 40 GHz. Comparison with the instrument noise and correcting for 5% atmospheric attenuation gives a cosmic signal rms contribution of 29 +/- 3 mu K (R-J) or 30 +/- 3 mu K relative to a Planck blackbody of 2.7 K. An estimate of the actual cosmic microwave background (CMB) sky signal requires taking into account the l space filter function of our experiment and analysis techniques, carried out in a companion paper. In addition to the robust detection of CMB anisotropies, we find a strong correlation between small portions of our maps and features in recent H alpha maps. In this work we describe the data set and analysis techniques leading to the maps, including data selection, filtering, pointing reconstruction, mapmaking algorithms, and systematic effects

The Background Emission Anisotropy Scanning Telescope ( BEAST) is a 2.2 m off-axis telescope with an eightelement mixed Q-band (38-45 GHz) and focal plane, designed for balloon-borne and ground-based studies of the cosmic microwave background (CMB). Here we present the CMB angular power spectrum calculated from 682 hr of data observed with the BEAST instrument. We use a binned pseudo-C l estimator (the MASTER method). We find results that are consistent with other determinations of the CMB anisotropy for angular wavenumbers l between 100 and 600. We also perform cosmological parameter estimation. The BEAST data alone produce a good constraint on k 1 À tot ¼ À0:074 AE 0:070, consistent with a flat universe. A joint parameter estimation analysis with a number of previous CMB experiments produces results consistent with previous determinations. Subject heading gs: cosmic microwave background -cosmology: observations -large-scale structure of universe Online material: color figure

No abstract

Context. Determining the spectral and spatial characteristics of the radio continuum of our Galaxy is an experimentally challenging endeavour for improving our understanding of the astrophysics of the interstellar medium. This knowledge has also become of paramount significance for cosmology, since Galactic emission is the main source of astrophysical contamination in measurements of the cosmic microwave background (CMB) radiation on large angular scales. Aims. We present a partial-sky survey of the radio continuum at 2.3 GHz within the scope of the Galactic Emission Mapping (GEM) project, an observational program conceived and developed to reveal the large-scale properties of Galactic synchrotron radiation through a set of self-consistent surveys of the radio continuum between 408 MHz and 10 GHz. Methods. The GEM experiment uses a portable and double-shielded 5.5-m radiotelescope in altazimuthal configuration to map 60-degree-wide declination bands from different observational sites by circularly scanning the sky at zenithal angles of 30 • from a constantly rotating platform. The observations were accomplished with a total power receiver, whose front-end high electron mobility transistor (HEMT) amplifier was matched directly to a cylindrical horn at the prime focus of the parabolic reflector. The Moon was used to calibrate the antenna temperature scale and the preparation of the map required direct subtraction and destriping algorithms to remove ground contamination as the most significant source of systematic error. Results. We used 484 h of total intensity observations from two locations in Colombia and Brazil to yield 66% sky coverage from δ = −51.• 73 to δ = +34.• 78. The observations in Colombia were obtained with a horizontal HPBW of 2.• 30 ± 0.• 13 and a vertical HPBW of 1.• 92 ± 0.• 18. The pointing accuracy was 6. 84 and the RMS sensitivity was 11.42 mK. The observations in Brazil were obtained with a horizontal HPBW of 2.• 31 ± 0.• 03 and a vertical HPBW of 1.• 82 ± 0.• 12. The pointing accuracy was 5. 26 and the RMS sensitivity was 8.24 mK. The zero-level uncertainty of the combined survey is 103 mK with a temperature scale error of 5% after direct correlation with the Rhodes/HartRAO survey at 2326 MHz on a T -T plot. Conclusions. The sky brightness distribution into regions of low and high emission in the GEM survey is consistent with the appearance of a transition region as seen in the Haslam 408 MHz and WMAP K-band surveys. Preliminary results also show that the temperature spectral index between 408 MHz and the 2.3 GHz band of the GEM survey has a weak spatial correlation with these regions; but it steepens significantly from high to low emission regions with respect to the WMAP K-band survey.

Abstract. We analytically investigate the use of a wire mesh ground screen (fence) and a halo of extension panels around a helically fed parabolic reflector in order to estimate the ground contribution to the antenna noise temperature in an experiment aimed at surveying the sky at decimeter wavelengths. We use geometric diffraction theory to model the effect of these screening and blocking shields when scanning in azimuth at tilt angles from zenith in the range 0 ø > Z > 45 ø. We report estimates based on existing formulas for monofilar axial-mode helical antennas with expected low-level sidelobes in the direction of the halo region. As long as there is no significant coupling between the near-field patterns of both the feed and the diffracting halo, estimates using the Fraunhofer approximation agree with those calculated with the Fresnel approach at a tilt angle •7'eq , which increases with the proximity of the diffracting edge from the near-/far-field boundary of the feed pattern. Our estimates show that for a fence of some 10-dB attenuation and high enough to level out the horizon profile at the prime focus of the antenna, the diffracted components dominate the contribution for tilt angles Z g 35 ø. The fence is the main diffractor when Z ;3 20 ø, but for Z ;3 25 ø its contribution becomes insensitive to the presence of the halo. On the other hand, if the attenuation is low (•ldB), the increase in ground solid angle with tilt angle makes the contribution due to transmission and ground exposure the dominant one.