Issue |
A&A
Volume 423, Number 1, August III 2004
|
|
---|---|---|
Page(s) | 111 - 119 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20040316 | |
Published online | 29 July 2004 |
Spectral index maps of the radio halos in Abell 665 and Abell 2163
1
Istituto di Radioastronomia – CNR, via P. Gobetti 101, 40129 Bologna, Italy e-mail: iferetti@ira.cnr.it
2
Dipartimento di Astronomia, Univ. Bologna, via Ranzani 1, 40127 Bologna, Italy
3
Naval Research Laboratory, Code 7213, Washington DC 20375, USA
Received:
23
February
2004
Accepted:
14
April
2004
New radio data at 330 MHz are presented for the rich clusters Abell 665 and Abell 2163, whose radio emission is characterized by the
presence of a radio halo. These images allowed us to derive the
spectral properties of the two clusters under study. The integrated
spectra of these halos between 0.3 GHz and 1.4 GHz are moderately
steep: and
,
for A665 and A2163, respectively. The spectral index maps, produced
with an angular resolution of the order of ~1´, show
features of the spectral index (flattening and patches), which are
indication of a complex shape of the radiating electron spectrum, and
are therefore in support of electron reacceleration models. Regions
of flatter spectrum are found to be related to the recent merger
activity in these clusters. This is the first strong confirmation
that the cluster merger supplies energy to the radio halo. In the
undisturbed cluster regions, the spectrum steepens with the distance
from the cluster center. This is interpreted as the result of the
combination of the magnetic field profile with the spatial
distribution of the reacceleration efficiency, thus allowing us to set
constraints on the radial profile of the cluster magnetic field.
Key words: radio continuum: general / galaxies: clusters: general / galaxies: clusters: individual: A665 / galaxies: clusters: individual: A2163 / galaxies: intergalactic medium / X-rays: galaxies: clusters
© ESO, 2004
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