Survey Observations to Study Chemical Evolution from High-mass Starless Cores to High-mass Protostellar Objects I: HC3N and HC5N

Abstract: We carried out survey observations of HC${3}$N and HC${5}$N in the 42$-$45 GHz band toward 17 high-mass starless cores (HMSCs) and 35 high-mass protostellar objects (HMPOs) with the Nobeyama 45 m radio telescope. We have detected HC${3}$N from 15 HMSCs and 28 HMPOs, and HC${5}$N from 5 HMSCs and 14 HMPOs, respectively. The average values of the column density of HC${3}$N are found to be ($5.7 \pm 0.7$)$\times 10^{12}$ and ($1.03 \pm 0.12$)$\times 10^{13}$ cm$^{-2}$ in HMSCs and HMPOs, respectively. The average values of the fractional abundance of HC${3}$N are derived to be ($6.6 \pm 0.8$)$\times 10^{-11}$ and ($3.6 \pm 0.5$)$\times 10^{-11}$ in HMSCs and HMPOs, respectively. We find that the fractional abundance of HC${3}$N decreases from HMSCs to HMPOs using the Kolmogorov-Smirnov test. On the other hand, its average value of the column density slightly increases from HMSCs to HMPOs. This may imply that HC${3}$N is newly formed in dense gas in HMPO regions. We also investigate the relationship between the column density of HC${3}$N in HMPOs and the luminosity-to-mass ratio ($L/M$), a physical evolutional indicator. The column density of HC${3}$N tends to decrease with increasing the $L/M$ ratio, which suggests that HC$_{3}$N is destroyed by the stellar activities.