ASHES. VI. Core-Scale CO Depletion

Under the typical conditions of infrared dark clouds, CO is removed from the gas phase and trapped onto the surface of dust grains by the so-called depletion process. This suggests that the CO-depletion factor (fD) can be a useful chemical indicator for identifying cold and dense regions (i.e., prestellar cores).

We have used the 1.3mm continuum and C18O (2-1) data observed at the resolution of ~5000 au in the ALMA Survey of 70{mu}m Dark High-mass Clumps in Early Stages (ASHES) to construct averaged maps of fD in 12 clumps to characterize the earliest stages of the high-mass star formation process. The average fD determined for 277 of the 294 ASHES cores follows an unexpected increase from the prestellar to the protostellar stage.