Results of the first year of data from the differential microwave radiometers on the Cosmic Background Explorer are presented. Statistically significant structure that is well described as ...scale-invariant fluctuations with a Gaussian distribution is shown. The rms sky variation, smoothed to a total 10-deg FWHM Gaussian, is 30 +/-5 micro-K for Galactic latitude greater than 20-deg data with the dipole anisotropy removed. The rms cosmic quadrupole amplitude is 13 +/-4 micro-K. The angular autocorrelation of the signal in each radiometer channel and cross-correlation between channels are consistent and give a primordial fluctuation power-law spectrum with index of 1.1 +/-0.5, and an rms-quadrupole-normalized amplitude of 16 +/-4 micro-K. These features are in accord with the Harrison-Zel'dovich spectrum predicted by models of inflationary cosmology.
ABSTRACT
We present the application of the fast independent component analysis (fastica) technique for blind component separation to polarized astrophysical emission. We study how the cosmic ...microwave background (CMB) polarized signal, consisting of E and B modes, can be extracted from maps affected by substantial contamination from diffuse Galactic foreground emission and instrumental noise. We implement Monte Carlo chains varying the CMB and noise realizations in order to asses the average capabilities of the algorithm and their variance. We perform the analysis of all‐sky maps simulated according to the Planck satellite capabilities, modelling the sky signal as a superposition of the CMB and of the existing simulated polarization templates of Galactic synchrotron. Our results indicate that the angular power spectrum of CMB E mode can be recovered on all scales up to ℓ≃ 1000, corresponding to the fourth acoustic oscillation, while the B‐mode power spectrum can be detected, up to its turnover at ℓ≃ 100, if the ratio of tensor to scalar contributions to the temperature quadrupole exceeds 30 per cent. The power spectrum of the cross‐correlation between total intensity and polarization, TE, can be recovered up to ℓ≃ 1200, corresponding to the seventh TE acoustic oscillation.
Gaussianity of the cosmological perturbations is one of the key predictions of standard inflation, but it is violated by other models of structure formation such as cosmic defects. We present the ...first test of the Gaussianity of the cosmic microwave background (CMB) on subdegree angular scales, where deviations from Gaussianity are most likely to occur. We apply the methods of moments, cumulants, the Kolmogorov test, the chi(2) test, and Minkowski functionals in eigen, real, Wiener-filtered, and signal-whitened spaces, to the MAXIMA-1 CMB anisotropy data. We find that the data, which probe angular scales between 10 arcmin and 5 deg, are consistent with Gaussianity. These results show consistency with the standard inflation and place constraints on the existence of cosmic defects.
We use the measurement of the cosmic microwave background taken during the MAXIMA-1 flight to estimate the bispectrum of cosmological perturbations. We propose an estimator for the bispectrum that is ...appropriate in the flat sky approximation, apply it to the MAXIMA-1 data, and evaluate errors using bootstrap methods. We compare the estimated value with what would be expected if the sky signal were Gaussian and find that it is indeed consistent, with a chi(2) per degree of freedom of approximately unity. This measurement places constraints on models of inflation.
The large-scale cosmic background anisotropy detected by the COBE Differential Microwave Radiometer (DMR) instrument is compared to the sensitive previous measurements on various angular scales, and ...to the predictions of a wide variety of models of structure formation driven by gravitational instability. The observed anisotropy is consistent with all previously measured upper limits and with a number of dynamical models of structure formation. For example, the data agree with an unbiased cold dark matter (CDM) model with H0 = 50 km/s Mpc and Delta-M/M = 1 in a 16 Mpc radius sphere. Other models, such as CDM plus massive neutrinos (hot dark matter (HDM)), or CDM with a nonzero cosmological constant are also consistent with the COBE detection and can provide the extra power seen on 5-10,000 km/s scales.
In this paper we present the Low Frequency Instrument (LFI), designed and developed as part of the Planck space mission, the ESA programme dedicated to precision imaging of the cosmic microwave ...background (CMB). Planck-LFI will observe the full sky in intensity and polarisation in three frequency bands centred at 30, 44 and 70 GHz, while higher frequencies (100–850 GHz) will be covered by the HFI instrument. The LFI is an array of microwave radiometers based on state-of-the-art indium phosphide cryogenic HEMT amplifiers implemented in a differential system using blackbody loads as reference signals. The front end is cooled to 20 K for optimal sensitivity and the reference loads are cooled to 4 K to minimise low-frequency noise. We provide an overview of the LFI, discuss the leading scientific requirements, and describe the design solutions adopted for the various hardware subsystems. The main drivers of the radiometric, optical, and thermal design are discussed, including the stringent requirements on sensitivity, stability, and rejection of systematic effects. Further details on the key instrument units and the results of ground calibration are provided in a set of companion papers.
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 2.3GHz 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 408MHz and 10GHz. 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 to . The observations in Colombia were obtained with a horizontal HPBW of and a vertical HPBW of . The pointing accuracy was and the RMS sensitivity was 11.42 mK. The observations in Brazil were obtained with a horizontal HPBW of and a vertical HPBW of . The pointing accuracy was and the RMS sensitivity was 8.24 mK. The zero-level uncertainty of the combined survey is 103mK with a temperature scale error of 5% after direct correlation with the Rhodes/HartRAO survey at 2326MHz 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 408MHz and WMAP K-band surveys. Preliminary results also show that the temperature spectral index between 408MHz and the 2.3GHz 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.
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