# Survey Observations to Study Chemical Evolution from High-Mass Starless Cores to High-Mass Protostellar Objects II. HC$_{3}$N and N$_{2}$H$^{+}$

## TL;DR

This survey investigates molecular line emissions in high-mass star-forming regions, revealing chemical evolution patterns that differ from low-mass regions, with implications for understanding massive star formation.

## Contribution

It provides the first comprehensive comparison of molecular abundances between high-mass starless cores and protostellar objects, highlighting unique chemical evolutionary trends.

## Key findings

- N2H+ detected in nearly all sources
- N(N2H+)/N(HC3N) ratio decreases from HMSCs to HMPOs
- Higher detection rates of cyanopolyynes in high-mass protostars

## 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.