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 \alpha = -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 } \mathrm { yr } .
Typical mass loss rates in the jet are found to be 1.4 \times 10 ^ { -5 } \mathrm { M } _ { \odot } \mathrm { yr ^ { -1 } } with associated momentum rates of the order ( 1 \ - - 2 ) \times 10 ^ { -2 } \mathrm { M } _ { \odot } \mathrm { km s ^ { -1 } yr } ^ { -1 } .