The impact of a young radio galaxy: clues from the cosmic-ray electron
  population
  In the framework of hierarchical structure formation AGN feedback shapes the
galaxy luminosity function. Low luminosity, galaxy-scale double radio sources
are ideal targets to investigate the interplay between AGN feedback and star
formation. We use VLA and BIMA observations to study the radio continuum
emission of NGC 3801 between 1.4 and 112.4 GHz. We find a prominent spectral
break at ~10 GHz, where the spectrum steepens as expected from cosmic-ray
electron (CRe) ageing. Using the equipartition magnetic field and fitting JP
models locally we create a spatially resolved map of the spectral age of the
CRe population. The spectral age of tau_int = 2.0 +/- 0.2 Myr agrees within a
factor of two with the dynamical age of the expanding X-ray emitting shells.
The spectral age varies only little across the lobes, requiring an effective
mixing process of the CRe such as a convective backflow of magnetized plasma.
The jet termination points have a slightly younger CRe spectral age, hinting at
in-situ CRe re-acceleration. Our findings support the scenario where the
supersonically expanding radio lobes heat the ISM of NGC 3801 via shock waves,
and, as their energy is comparable to the energy of the ISM, are clearly able
to influence the galaxy's further evolution.
