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2.3. Radio source – environment interactions 17
Table 2.1: Typical parameters describing the X-ray 1 emitting atmospheres in clusters, groups and
massive ellipticals.
environment L X n e (0) r c β kT
[erg s −1 ] [cm −3 ] [kpc] [keV]
cluster 10 43−45 10 −3 100-300 0.4-0.8 2-6
group 10 41−44 10 −3 − 10 −4 20-200 0.3-0.9 0.3-2
elliptical 10 39−41 0.1 5-20 ” 0.5-1.5
1 in the soft X-ray energy band≃0.2-10 keV.
Figure 2.2: Composite image of the galaxy cluster MS0735.6 7421 Hubble Space Telescope
(optical) superimposed on Chandra X-ray (blue) and Very Large Array at 330 MHz (red). The
X-ray data show the emission of hot gas at∼ 5× 10 7 K and two cavities, each roughly 200 kpc in
diameter coincident with radio lobes. Taken from McNamara et al. (2005).
2.3 Radio source – environment interactions
2.3.1 X-ray cavities and their content
An increasing number of clusters, groups and giant ellipticals show regions of X-ray surface
brightness depressions which appear as holes embedded in a brighter emission (see McNamara
& Nulsen 2007 for a review).
The surface brightness of such holes is around 20-40% below that of the surroundings. They
are commonly observed coincident with radio lobes and generally referred to as “cavities”. An
example is given in Fig. 2.2: the Chandra image displays the soft X-ray emission of the cluster
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