Survey Observations to Study Chemical Evolution from High-Mass Starless Cores to High-Mass Protostellar Objects II. HC${}_3$N and N${}_2$H${}^{+}$

Abstract

We have carried out survey observations of molecular emission lines from HC${}_3$N, N${}_2$H${}^{+}$, CCS, and cyclic-C${}_3$H${}_2$ in the 81$-$94 GHz band toward 17 high-mass starless cores (HMSCs) and 28 high-mass protostellar objects (HMPOs) with the Nobeyama 45-m radio telescope. We have detected N${}_2$H${}^{+}$ in all of the target sources except one and HC${}_3$N in 14 HMSCs and in 26 HMPOs. We investigate the $N$(N${}_2$H${}^{+}$)/$N$(HC${}_3$N) column density ratio as a chemical evolutionary indicator of massive cores. Using the Kolmogorov-Smirnov (K-S) test and Welch's t test, we confirm that the $N$(N${}_2$H${}^{+}$)/$N$(HC${}_3$N) ratio decreases from HMSCs to HMPOs. This tendency in high-mass star-forming regions is opposite to that in low-mass star-forming regions. Furthermore, we found that the detection rates of carbon-chain species (HC${}_3$N, HC${}_5$N, and CCS) in HMPOs are different from those in low-mass protostars. The detection rates of cyanopolyynes (HC${}_3$N and HC${}_5$N) are higher and that of CCS is lower in high-mass protostars, compared to low-mass protostars. We discuss a possible interpretation for these differences.

arXiv commentAccepted for publication in The Astrophysical Journal, 29 pages, 16 figures, 8 tables

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• Cyanopolyyne Chemistry around Massive Young Stellar Objects
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