PEACHES IV: Tracing the Formation & Evolution of C${}_2$H 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 ALMA ACA observations, we investigate the C${}_2$H 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 C${}_2$H emission and the protostellar outflow cavity walls, and a consistent spatial anti-correlation 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${}^{14}$ -- 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 surface of Class II disks must happen rapidly, sometime just after the embedded stage.