CH3CN Observations toward Southern Massive Star-forming Regions

In an effort to identify very young sites of massive star formation, we have conducted a survey for hot and dense molecular cores toward a sample of 17 southern sources. The sample consists of sources with IRAS color characteristics of ultracompact H II regions for which high-density molecular material had previously been detected. We observed the J=5-4, 6-5, 8-7, and 12-11 rotational transitions of CH₃CN and derived rotation temperatures and column densities using the population-diagram technique. We identify four sources with a high-temperature molecular component (T_rot>90 K) as new candidates for hot molecular cores. We also observed the transitions H35α, CS J=3-2, and the continuum in the 3, 2 mm bands toward 17 sources, and the 1.3 mm continuum, H41α and ¹³CO J=2-1 transitions toward 10 sources. Eight sources show blue and red wings in the CS J=3-2 line, whereas three sources show wings in the ¹³CO J=2-1 spectra, suggestive of molecular outflows. Our continuum and recombination line data show that the 91 GHz continuum emission is dominated by free-free emission from ionized regions, whereas at 147 GHz emission from dust grains contributes significantly.