A search for ionized jets towards massive young stellar objects
  Radio continuum observations using the Australia telescope compact array at
5.5, 9.0, 17.0 and 22.8 GHz have detected free-free emission associated with 45
of 49 massive young stellar objects and HII regions. Of these, 26 sources are
classified as ionized jets (12 of which are candidates), 2 as ambiguous jets or
disc winds, 1 as a disc-wind, 14 as HII regions and 2 were unable to be
categorised. Classification as ionized jets is based upon morphology, radio
flux and spectral index, in conjunction with previous observational results at
other wavelengths. Radio-luminosity and momentum are found to scale with
bolometric luminosity in the same way as low-mass jets, indicating a common
mechanism for jet production across all masses. In 13 of the jets, we see
associated non-thermal/optically-thin lobes resulting from shocks either
internal to the jet and/or at working surfaces. Ten jets display non-thermal
(synchrotron emission) spectra in their lobes, with an average spectral index
of -0.55 consistent with Fermi acceleration in shocks. This shows that magnetic
fields are present, in agreement with models of jet formation incorporating
magnetic fields. Since the production of collimated radio jets is associated
with accretion processes, the results presented in this paper support the
picture of disc-mediated accretion for the formation of massive stars with an
upper-limit on the jet phase lasting approximately $6.5 \times 10^4 yr$.
Typical mass loss rates in the jet are found to be $1.4 \times 10^{-5} M_\odot
yr^{-1}$ with associated momentum rates of the order $(1-2) \times 10^{-2}
M_\odot km s^{-1} yr^{-1}$.
