PEACHES IV: Tracing the Formation & Evolution of C2H in Perseus Low-Mass Protostars
Abstract
The radical hydrocarbon molecule C2H is widely detected in various stages of star and planet formation, and has emerged as a useful tracer of high-C/O gas within the photochemically active surface layers of mature (Class II) protoplanetary disks. However, the chemistry and evolution of C2H within younger (Class 0/I) protostars remains much more poorly understood. Here, using data observed as part of the PEACHES survey along with new ALMA ACA observations, we investigate the C2H emission towards an unbiased sample of 35 Class 0/I low-mass protostars in Perseus. With this large sample, we identify a clear association between C2H emission and the protostellar outflow cavity walls, and a consistent spatial anti-correlation between C2H and SO emission. Together, these trends confirm that C2H is tracing photochemically active, O-poor gas in these younger sources. We fitted the C2H spectra with a simple LTE model to yield column density maps, and find values ranging from 1014 -- 1015 cm-2 in these sources. We also looked for trends in the C2H emission morphology as a function of various protostellar evolutionary metrics, but find no clear patterns: the C2H emission remains spatially extended in most sources, independent of age. This indicates that the transition to the compact C2H emission observed on the surface of Class II disks must happen rapidly, sometime just after the embedded stage.
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