Issue |
A&A
Volume 412, Number 2, December III 2003
|
|
---|---|---|
Page(s) | 373 - 385 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20031434 | |
Published online | 28 November 2003 |
Measuring the cluster magnetic field power spectra from Faraday rotation maps of Abell 400, Abell 2634 and Hydra A
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 1317, 85741 Garching, Germany
Corresponding author: C. Vogt, cvogt@mpa-garching.mpg.de
Received:
10
June
2003
Accepted:
4
September
2003
We apply a novel technique of Faraday Rotation measure (RM) map
analysis to three galaxy clusters, Abell 400, Abell 2634 and Hydra A,
in order to estimate cluster magnetic field strengths, length scales
and power spectra. This analysis – essentially a correlation analysis
– is based on the assumption that the magnetic fields are
statistically isotropically distributed across the Faraday screen. We
investigate the difficulties involved in the application of the
analysis to observational data. We derive magnetic power spectra for
three clusters, i.e. Abell 400, Abell 2634 and Hydra A, and discuss
influences on their shapes caused by the observational nature of the
data such as limited source size and resolution. We successfully apply
various tests to validate our assumptions. We show that magnetic
fluctuations are probed on length scales ranging over at least one
order of magnitude. Using this range for the determination of magnetic
field strength of the central cluster gas yields 3 μG in Abell 2634, 6 μG in Abell 400 and 12 μG in Hydra A as conservative
estimates. The magnetic field autocorrelation length was
determined to be 4.9 kpc for Abell 2634, 3.6 kpc for Abell 400 and 0.9
kpc for Hydra A. We show that the RM autocorrelation length
is larger than the magnetic field autocorrelation
length
– for the three clusters studied, we found
– and thus, they are not equal as
often assumed in the literature. Furthermore, we investigate in a
response analysis if it is possible to determine spectral slopes of
the power spectra. We find that integrated numbers can be reliably
determined from this analysis but differential parameters such as
spectral slopes have to be treated differently. However, our response
analysis results in spectral slopes of the power spectra of spectral
indices
to 2.0 suggesting that Kolmogorov spectra
(
) are possible but flatter spectral slopes than
can be excluded.
Key words: radiation mechanism: non-thermal / galaxies: active / interplanetary medium / galaxies: cluster: general / radio continuum: general
© ESO, 2003
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