EDP Sciences
Free access
Issue A&A
Volume 396, Number 2, December III 2002
Page(s) 463 - 471
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20021392



A&A 396, 463-471 (2002)
DOI: 10.1051/0004-6361:20021392

Polarization properties of extragalactic radio sources and their contribution to microwave polarization fluctuations

D. Mesa1, C. Baccigalupi

2, 3, G. De Zotti4, L. Gregorini5, 6, K.-H. Mack7, 5, 8, M. Vigotti5 and U. Klein8

1  Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
    e-mail: mesa@mostro.pd.astro.it
2  SISSA, International School for Advanced Studies, Via Beirut 2-4, 34014 Trieste, Italy
    e-mail: bacci@sissa.it
3  Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Mailstop 50-205, Berkeley, CA 94720, USA
4  Osservatorio Astronomico di Padova, INAF, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
    e-mail: dezotti@pd.astro.it
5  IRA/CNR, Via Gobetti 101, 40129 Bologna, Italy
6  Dipartimento di Fisica, Università di Bologna, Via Irnerio 46, 40126 Bologna, Italy
7  ASTRON/NFRA, Postbus 2, 7990 AA Dwingeloo, The Netherlands
    e-mail: mack@astron.nl
8  Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

(Received 5 July 2002 / Accepted 2 September 2002 )

Abstract
We investigate the statistical properties of the polarized emission of extragalactic radio sources and estimate their contribution to the power spectrum of polarization fluctuations in the microwave region. The basic ingredients of our analysis are the NVSS polarization data, the multifrequency study of polarization properties of the B3-VLA sample (Mack et al. 2002) which has allowed us to quantify Faraday depolarization effects, and the 15 GHz survey by Taylor et al. (2001), which has provided strong constraints on the high-frequency spectral indices of sources. The polarization degree of both steep- and flat-spectrum sources at 1.4 GHz is found to be anti-correlated with the flux density. The median polarization degree at 1.4 GHz of both steep- and flat-spectrum sources brighter than $S(1.4\,\hbox{GHz})=80\,$mJy is $\simeq$ $2.2\%$. The data by Mack et al. (2002) indicate a substantial mean Faraday depolarization at 1.4 GHz for steep spectrum sources, while the depolarization is undetermined for most flat/inverted-spectrum sources. Exploiting this complex of information we have estimated the power spectrum of polarization fluctuations due to extragalactic radio sources at microwave frequencies.

We confirm that extragalactic sources are expected to be the main contaminant of Cosmic Microwave Background (CMB) polarization maps on small angular scales. At frequencies <30 GHz the amplitude of their power spectrum is expected to be comparable to that of the E-mode of the CMB. At higher frequencies, however, the CMB dominates.


Key words: radio continuum: galaxies -- polarization -- cosmic microwave background

Offprint request: G. De Zotti, dezotti@pd.astro.it




© ESO 2002

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)