Multi-wavelength observations of Southern Hot Molecular Cores traced by methanol masers - I. Ammonia and 24 GHz Continuum Data

Abstract

We present observations of the (1,1), (2,2), (4,4) and (5,5) inversion transitions of para-ammonia (NH3) and 24 GHz continuum, taken with the Australia Telescope Compact Array toward 21 southern Galactic hot molecular cores traced by 6.7 GHz methanol maser emission. We detect NH3(1,1) emission toward all 21 regions and 24 GHz continuum emission toward 12 of the regions, including 6 with no reported 8 GHz continuum counterparts. In total, we find the 21 regions contain 41 NH3(1,1) cores. We extract characteristic spectra for every core at each of the NH3 transitions and present both integrated intensity maps and channel maps for each region. The NH3(4,4)+(5,5) emission is always unresolved and found at the maser position indicating that the methanol masers are found at the warmest part of the core. We observe large asymmetries in the NH3(1,1) hyperfine line profiles and conclude this is due to a number of dense, small clumps within the beam. We derive properties of the ionised gas and find the 24 GHz continuum sources not detected at 8 GHz are always coincident with both NH3 and methanol masers in contrast to those detected at 8 + 24 GHz which are generally offset from the methanol masers. We investigate the possibility that the former may be hyper-compact HII regions. Finally, we separate the cores into five groups, based on their association with NH3, methanol maser and continuum emission. From the different physical properties of the cores in the groups, we discuss the possibility that these groups may represent cores at different evolutionary stages of the massive star formation process.