EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 397/1 Article
Free access article

Issue A&A
Volume 397, Number 1, January I 2003
Page(s) 53 - 61
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20021474



A&A 397, 53-61 (2003)
DOI: 10.1051/0004-6361:20021474

The diffuse radio emission from the Coma cluster at 2.675 GHz and 4.85 GHz

M. Thierbach1, 2, U. Klein3 and R. Wielebinski1

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2  SMTO, Steward Observatory, The University of Arizona, 933 N. Cherry Avenue, Tucson, Arizona 85721, USA
3  Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

(Received 5 October 2001 / Accepted 7 October 2002 )

Abstract
We present new measurements of the diffuse radio halo emission from the Coma cluster of galaxies at 2.675 GHz and 4.85 GHz using the Effelsberg 100-m telescope. After correction for the contribution from point sources we derive the integrated flux densities for the halo source (Coma C), $S_{\rm 2.675~GHz}=(107\pm 28)~{\rm mJy}$ and $S_{\rm 4.85~GHz}=(26\pm 12)~{\rm mJy}$. These values verify the strong steepening of the radio spectrum of Coma C at high frequencies. Its extent strongly depends on frequency, at 4.85 GHz it is only marginally visible. The measurement at 4.85 GHz is the first flux density determination for Coma C at this high frequency. In order to quantify the spectral steepening we compare the expectations for the spectrum of Coma C with the observations, resorting to basic models for radio halo formation. The in-situ acceleration model provides the best fit to the data. From equipartition assumptions we estimate a magnetic field strength $B_{\rm eq}=0.57\,(1+k)^{0.26}\,{\rm\mu G}$ in the intracluster medium of Coma, where k is the energy ratio of the positively and negatively charged particles.

As a by-product of the 2.675 GHz observation we present a new flux density for the diffuse emission of the extended source 1253+275 ( $S_{\rm 2.675GHz}=112\pm 10$). This measurement provides a smaller error range for the power-law fit to the spectrum ( $\alpha=1.18\pm 0.02$) compared to previous investigations and yields an equipartition magnetic field strength of $B_{\rm eq}=0.56\,(1+k)^{0.24}\,{\rm\mu G}$.


Key words: galaxies: clusters: individual: Coma cluster, 1253+275 -- galaxies: intergalactic medium

Offprint request: M. Thierbach, thierb@mpifr-bonn.mpg.de

SIMBAD Objects



© ESO 2003


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.