The intracluster magnetic field power spectrum in A2199

¹ Dipartimento di Fisica, Università degli studi di Cagliari, Cittadella Universitaria, 09042 Monserrato (CA), Italy
e-mail: vvacca@oa-cagliari.inaf.it
² INAF – Osservatorio Astronomico di Cagliari, Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy
³ INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁴ Dipartimento di Astronomia, Univ. Bologna, via Ranzani 1, 40127 Bologna, Italy
⁵ National Radio Astronomy Observatory, Socorro, NM 87801, USA
⁶ Department of Physics and Astronomy, University of New Mexico, Albuquerque NM, 87131, USA

Received: 1 February 2011
Accepted: 2 December 2011

Abstract

Aims. We investigate the magnetic field power spectrum in the cool core galaxy cluster A2199 by analyzing the polarized emission of the central radio source 3C 338.

Methods. The polarized radiation from the radio emitting plasma is modified by the Faraday rotation as it passes through the magneto-ionic intracluster medium. We use Very Large Array observations between 1665 and 8415 MHz to produce detailed Faraday rotation measure and fractional polarization images of the radio galaxy. We simulate Gaussian random three-dimensional magnetic field models with different power-law power spectra and we assume that the field strength decreases radially with the thermal gas density as n_e^η. By comparing the synthetic and the observed images with a Bayesian approach, we constrain the strength and structure of the magnetic field associated with the intracluster medium.

Results. We find that the Faraday rotation toward 3C 338 in A2199 is consistent with a magnetic field power law power spectrum characterized by an index n =  (2.8 ± 1.3) between a maximum and a minimum scale of fluctuation of Λ_max =  (35 ± 28) kpc and Λ_min =  (0.7 ± 0.1) kpc, respectively. By including in the modeling X-ray cavities coincident with the radio galaxy lobes, we find a magnetic field strength of ⟨B₀⟩ =  (11.7 ± 9.0) μG at the cluster center. Further out, the field decreases with the radius following the gas density to the power of η = (0.9 ± 0.5).