Presentation #506.03 in the session “Astrochemistry 2”.
Dense molecular cloud clumps that are dark at 70μm wavelengths are promising candidates for the initial stages of stellar protocluster evolution, but their ages, star formation efficiency, and ultimate capability of forming high-mass stars are uncertain. To this end we present Karl G. Jansky Very Large Array 22-25 GHz observations of the carbon chain molecules HC5N (J=9➝8), HC7N (J=20➝19 and J=21➝20), and CCS (JN=21➝10) , which are diagnostic of young gas, towards 12 high-mass 70μm-dark clumps (600-3000 Solar masses). We detect HC5N and CCS towards all of the target sources except one, which was likely mis-identified as a 70 μm-dark clump. While not detected in any sources individually, HC7N is detected in the stacked spectrum of all the sources. We calculate molecular abundances of the species and compare the measured values to dark cloud chemistry models. The models show that the clumps are all less than approximately 0.5 Myr old while at densities of n(H2) = 104 cm-3. As these sources were blindly selected from the Galactic Plane, the uniformly young ages are inconsistent with the conclusion that these clumps are starless because they are inefficient at forming high-mass stars. Instead, these findings support the conclusion that high-mass stars have likely not had sufficient time to form.