Survey Observations to Study Chemical Evolution from High-mass Starless Cores to High-mass Protostellar Objects. II. HC₃N and N₂H⁺

Abstract

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 prorostellar 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 find 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.