Radiative ages in a representative sample of low luminosity radio galaxies

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Two frequency observations, mainly at 1.4 and 5 GHz from the VLA, have been used to study spectral variations along the lobes of some nearby low luminosity radio galaxies that constitute a representative sample selected from the B2 catalogue. The variations of the spectral index have been interpreted as being due to synchrotron and inverse Compton losses and characteristic spectral ages are deduced for the relativistic electrons. The radiative ages are in the range of several 10⁷ years. These ages correlate well with the source sizes. They also appear to be consistent with dynamical ages determined from ram-pressure arguments, if we make reasonable assumptions about the ambient gas density and allow for very moderate deviations from the equipartition conditions. There appears to be a significant difference between the radiative ages of sources in our sample and those of more powerful 3CR radio sources. We briefly discuss the possibility of re-acceleration processes and indicate some objects where these may occur.