Chemical Survey toward Young Stellar Objects in the Perseus Molecular Cloud Complex

Abstract

The chemical diversity of gas in low-mass protostellar cores is widely recognized. In order to explore the origin of this diversity, a survey of chemical composition toward 36 Class 0/I protostars in the Perseus molecular cloud complex, which are selected in an unbiased way under certain physical conditions, has been conducted with IRAM 30 m and NRO 45 m telescope. Multiple lines of C<SUB>2</SUB>H, c-C<SUB>3</SUB>H<SUB>2</SUB>, and CH<SUB>3</SUB>OH have been observed to characterize the chemical composition averaged over a 1000 au scale around the protostar. The derived beam-averaged column densities show significant chemical diversity among the sources, where the column density ratios of C<SUB>2</SUB>H/CH<SUB>3</SUB>OH are spread out by two orders of magnitude. From previous studies, the hot corino sources have abundant CH<SUB>3</SUB>OH but deficient C<SUB>2</SUB>H, their C<SUB>2</SUB>H/CH<SUB>3</SUB>OH column density ratios being relatively low. In contrast, the warm-carbon-chain chemistry (WCCC) sources are found to reveal the high C<SUB>2</SUB>H/CH<SUB>3</SUB>OH column density ratios. We find that the majority of the sources have intermediate characters between these two distinct chemistry types. A possible trend is seen between the C<SUB>2</SUB>H/CH<SUB>3</SUB>OH ratio and the distance of the source from the edge of a molecular cloud. The sources located near cloud edges or in isolated clouds tend to have a high C<SUB>2</SUB>H/CH<SUB>3</SUB>OH ratio. On the other hand, the sources having a low C<SUB>2</SUB>H/CH<SUB>3</SUB>OH ratio tend to be located in the inner regions of the molecular cloud complex. This result gives an important clue toward understanding the origin of the chemical diversity of protostellar cores in terms of environmental effects.