ALMA Datacubes and Continuum Maps of the Irradiated Western Wall in Carina

Abstract

We present ALMA observations of the continuum and line emission of $^{12}$CO, $^{13}$CO, C$^{18}$O, 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 H$_2$, to [C I], to C$^{18}$O with distance into the PDR front. Emission from optically thick $^{12}$CO extends across the region, while $^{13}$CO, [C I] and especially C$^{18}$O 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 datacube of C$^{18}$O. The mass distribution of these objects is similar to that of the stellar IMF. 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 C$^{18}$O clumps and continuum cores appear starless, with no pillars present. However, the densest portion of the cloud lies closest to the PDR, and the C$^{18}$O emission is flattened along the radiation front.