Alma Mater Studiorum Universit`a degli Studi di Bologna ... - Inaf

Chapter 4
Structure of the magneto-ionic medium
around the Fanaroff-Riley Class I radio
galaxy 3C 449 ∗
M
agnetic fields associated with galaxy groups deserve to be investigated in more detail,
since their environments are more representative than those of rich clusters. Moreover,
observations, analytical models and MHD simulations of galaxy clusters all suggest that the
magnetic-field intensity should scale with the thermal gas density (e.g. Brunetti et al. 2001;
Dolag 2006; Guidetti et al. 2008; Bonafede et al. 2010). A key question is whether the relation
between magnetic field strength and density in galaxy groups is a continuation of this trend.
This Chapter presents a detailed analysis of Faraday rotation in 3C 449, a bright, extended radio
source hosted by the central galaxy of a nearby group. With the aim of shedding new light on
the environment around this source, I derive the statistical properties of the magnetic field from
observations of Faraday rotation, following the method developed by Murgia et al. (2004). I use
numerical simulations to predict the Faraday rotation for different strengths and power spectra of
the magnetic field.
With the assumed cosmology, at the distance of 3C 449 1 arcsec corresponds to 0.342 kpc.
4.1 The radio source 3C 449: general properties
I image and model the Faraday rotation distribution across the giant FR I radio source 3C 449,
whose environment is very similar to that of 3C 31. The optical counterpart of 3C 449,
UGC 12064, is a dumb-bell galaxy and is the most prominent member of the group of galaxies
∗ Guidetti et al. 2010, A&A, 514, 50
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