Power spectrum of the polarized diffuse Galactic radio emission

Free access article

Issue		A&A Volume 372, Number 1, June II 2001


Page(s)		8 - 21
Section		Cosmology
DOI		http://dx.doi.org/10.1051/0004-6361:20010414

A&A 372, 8-21 (2001)
DOI: 10.1051/0004-6361:20010414

Power spectrum of the polarized diffuse Galactic radio emission

C. Baccigalupi¹, C. Burigana², F. Perrotta^{1, 3}, G. De Zotti³, L. La Porta², D. Maino⁴, M. Maris⁴ and R. Paladini¹

¹ SISSA/ISAS, Via Beirut 4, 34014 Trieste, Italy
² ITeSRE/CNR, Via P. Gobetti 101, 40129 Bologna, Italy
³ Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
⁴ Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy

(Received 11 September 2000 / Accepted 16 March 2001)

Abstract
We have analyzed the available polarization surveys of the Galactic emission to estimate to what extent it may be a serious hindrance to forthcoming experiments aimed at detecting the polarized component of Cosmic Microwave Background (CMB) anisotropies. Regions were identified for which independent data consistently indicate that Faraday depolarization may be small. The power spectrum of the polarized emission, in terms of antenna temperature, was found to be described by $C^{\rm P}_{\ell}\simeq (1.2\pm 0.8) 10^{-9}\cdot (\ell / 450)^{-1.8\pm 0.3}\cdot (\nu/ 2.4 {\rm GHz})^{-5.8}$ K², from arcminute to degree scales. Data on larger angular scales ( $\ell\le 100$ ) indicate a steeper slope ~ $\ell^{-3}$ . We conclude that polarized Galactic emission is unlikely to be a serious limitation to CMB polarization measurements at the highest frequencies of the MAP and PLANCK-LFI instruments, at least for $\ell\ge 50$ and standard cosmological models. The weak correlation between polarization and total power and the low polarization degree of radio emission close to the Galactic plane is interpreted as due to large contributions to the observed intensity from unpolarized sources, primarily strong HII regions, concentrated on the Galactic plane. Thus estimates of the power spectrum of total intensity at low Galactic latitudes are not representative of the spatial distribution of Galactic emission far from the plane. Both total power and polarized emissions show highly significant deviations from a Gaussian distribution.

Key words: polarization -- ISM: structure -- Galaxy: general -- cosmology: cosmic microwave background -- radio continuum: ISM

Offprint request: C. Baccigalupi, bacci@sissa.it

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