PEACHES. IV. Tracing the Formation and Evolution of C₂H in Perseus Low-mass Protostars

Abstract The radical hydrocarbon molecule C 2 H 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 C 2 H 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 C 2 H 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 C 2 H emission and the protostellar outflow cavity walls, and a consistent spatial anticorrelation between C 2 H and SO emission. Together, these trends confirm that C 2 H is tracing photochemically active, O-poor gas in these younger sources. We fitted the C 2 H spectra with a simple LTE model to yield column density maps, and find values ranging from 10 14 to 10 15 cm −2 in these sources. We also looked for trends in the C 2 H emission morphology as a function of various protostellar evolutionary metrics, but find no clear patterns; the C 2 H emission remains spatially extended in most sources, independent of age. This indicates that the transition to the compact C 2 H emission observed on the surfaces of Class II disks must happen rapidly, sometime just after the embedded stage.