2022AJ....164..257H

We present Atacama Large Millimeter/submillimeter Array observations of the continuum and line emission of ¹²CO, ¹³CO, C¹⁸O, and [C I] for a portion of the G287.38-0.62 (Car 1-E) region in the Carina star-forming complex. The new data record how a molecular cloud responds on subarcsecond scales when subjected to a powerful radiation front, and provide insights into the overall process of star formation within regions that contain the most-massive young stars. The maps show several molecular clouds superpose upon the line of sight, including a portion of the Western Wall, a highly irradiated cloud situated near the young star cluster Trumpler 14. In agreement with theory, there is a clear progression from fluoresced H₂, to [C I], to C¹⁸O with distance into the photodissociation region (PDR) front. Emission from optically thick ¹²CO extends across the region, while ¹³CO, [C I] and especially C¹⁸O are more optically thin, and concentrate into clumps and filaments closer to the PDR interface. Within the Western Wall cloud itself we identify 254 distinct core-sized clumps in our data cube of C¹⁸O. The mass distribution of these objects is similar to that of the stellar initial mass function. Aside from a large-scale velocity gradient, the clump radial velocities lack any spatial coherence size. There is no direct evidence for triggering of star formation in the Western Wall in that its C¹⁸O clumps and continuum cores appear starless, with no pillars present. However, the densest portion of the cloud lies closest to the PDR, and the C¹⁸O emission is flattened along the radiation front.