2025ApJ...990..150A

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 Atacama Large Millimeter/submillimeter Array Atacama Compact Array observations, we investigate the C₂H emission toward 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 anticorrelation 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 to 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 surfaces of Class II disks must happen rapidly, sometime just after the embedded stage.