X-ray cooling luminosity (see Sect. 3) versus cavity power (calculated as P_cav = E/t_b) from Gitti et al. (2012). NGC 5141 is the magenta star (see Table 2 for values). The cavity energy is estimated as E = 4pV. Different symbols denote systems in different samples: green triangles are clusters from Bîrzan et al. (2008), red squares are giant ellipticals from Cavagnolo et al. (2010) and blue circles are groups from O’Sullivan et al. (2011). NGC 3608, which is part of the Cavagnolo et al. (2010) sample, is highlighted as the yellow-filled square with red edges. The diagonal line indicates P_cav = L_cool. If cooling is exactly balancing heating, the content of the X-ray cavities is fully relativistic and P_cav = P_jet, thus the data points should be on the line.