CHaMPs of Star Formation: A Galactic Census of High- and Medium-Mass Protostars

We report preliminary results of an unbiased survey for higher-mass protostellar or protocluster dense molecular cores. In a 20°x3° swath of the Galactic Plane, the NANTEN surveys have revealed ~140 cores detectable in C18O, covering only ~1% of the projected area of the Plane. We have now examined 52 of these cores in a variety of traditional dense gas tracers at much higher resolution than the NANTEN maps, using the Mopra antenna and the Compact Array, both part of the Australia Telescope National Facility. We have mapped the J=1-0 lines of HCO+, H13CO+, and N2H+, and the (J,K)=(1,1) inversion line of NH3. Apart from HCO+, which is fairly widespread, we have found only ~25% of the C18O cores contain truly dense gas as traced by the other species; only ~15% of the cores have strong (>2.0 K) HCO+ emission. This alone suggests that the dense phase of a molecular core is relatively short-lived.