Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...464...18m&link_type=abstract
Astrophysical Journal v.464, p.18
Astronomy and Astrophysics
Astronomy
3
Cosmology: Cosmic Microwave Background, Methods: Numerical
Scientific paper
Various techniques for extracting the power spectrum from a map of cosmic background anisotropies - (CBAs) have been discussed in the literature; the best signal-to-noise ratio is expected for a large and symmetric map. Unfortunately, many of the data sets already available do not provide a map; typically they consist of a limited number of long stripes over the sky. We discuss a straightforward method for estimating the power spectral index from these data sets. The method (called "Δ statistics") is tested over the infrared IRAS map, where it allows us to avoid the effects of some artifacts, like extended stripes with different detector responsivity. We show that it is possible to extend the analysis down to a differential brightness of 0.05 MJy sr-1 at 100 μm, with an angular resolution of 3'; at these low levels dust anisotropies have a spectral power index -2.5 ≤ n ≤ - . While these "local" values of n are not in disagreement with a unique value of n if the cosmic variance is taken into account, the selection of clean sky regions where fluctuations are at a minimum will peak up zones with flat power spectra, thereby suggesting possible significant contributions to CBA at small angular scales. The data provided by balloon experiments are particularly suitable for Δ statistics analysis, being taken while the gondola is slowly moving parallel to the horizon. The sky stripes explored by ULISSE and ARGO experiments are reanalyzed and provide values of nULISSE = -2.2±0.7 around l = 20 and nARGO = -1.4±0.4 around l = 200. These values are independent of COBE normalization, calibration uncertainties, and, to a great extent, of the details of the experiment, such as beam size, modulation amplitude, and type.
Guarini Gianfranco
Melchiorri Bianca
Melchiorri Francesco
Signore Monique
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