Internal entrainment and the origin of jet-related broad-band emission
  in Centaurus A
  The dimensions of Fanaroff-Riley class I jets and the stellar densities at
galactic centres imply that there will be numerous interactions between the jet
and stellar winds. These may give rise to the observed diffuse and 'knotty'
structure of the jets in the X-ray, and can also mass load the jets. We
performed modelling of internal entrainment from stars intercepted by Centaurus
A's jet, using stellar evolution- and wind codes. From photometry and a
code-synthesised population of 12 Gyr (Z = 0.004), 3 Gyr (Z = 0.008) and 0 - 60
Myr (Z = 0.02) stars, appropriate for the parent elliptical NGC 5128, the total
number of stars in the jet is ~ 8 x 10^8. Our model is energetically capable of
producing the observed X-ray emission, even without young stars. We also
reproduce the radio through X-ray spectrum of the jet, albeit in a downstream
region with distinctly fewer young stars, and recover the mean X-ray spectral
index. We derive an internal entrainment rate of ~ 2.3 x 10^-3 Msun yr^-1 which
implies substantial jet deceleration. Our absolute nucleosynthetic yields for
the AGB stellar population in the jet show the highest amounts for 4He, 16O,
12C, 14N and 20Ne. If some of the events at >= 55 EeV detected by the Pierre
Auger Observatory originate from internal entrainment in Centaurus A, we
predict that their composition will be largely intermediate-mass nuclei with
16O, 12C and 14N the key isotopes.
