Search for ionized jets towards high-mass young stellar objects
  We are carrying out multi-frequency radio continuum observations, using the
Australia Telescope Compact Array, to systematically search for collimated
ionized jets towards high-mass young stellar objects (HMYSOs). Here we report
observations at 1.4, 2.4, 4.8 and 8.6 GHz, made with angular resolutions of
about 7, 4, 2, and 1 arcsec, respectively, towards six objects of a sample of
33 southern HMYSOs thought to be in very early stages of evolution. The objects
in the sample were selected from radio and infrared catalogs by having positive
radio spectral indices and being luminous (L_bol > 20,000 L_sun), but
underluminous in radio emission compared to that expected from its bolometric
luminosity. This criteria makes the radio sources good candidates for being
ionized jets. As part of this systematic search, two ionized jets have been
discovered: one previously published and the other reported here. The rest of
the observed candidates correspond to three hypercompact hii regions and two
ultracompact hii regions. The two jets discovered are associated with two of
the most luminous (70,000 and 100,000 Lsun) HMYSOs known to harbor this type of
objects, showing that the phenomena of collimated ionized winds appears in the
formation process of stars at least up to masses of ~ 20 M_sun and provides
strong evidence for a disk-mediated accretion scenario for the formation of
high-mass stars. From the incidence of jets in our sample, we estimate that the
jet phase in high-mass protostars lasts for 40,000 yr.
