摘要：Aims. We aim to systematically study the properties of the different transitions of the dense molecular gas tracer HC3N in galaxies.
Methods. We have conducted single-dish observations of HC3N emission lines towards a sample of nearby gas-rich galaxies. HC3N(J = 2−1) was observed in 20 galaxies with the Effelsberg 100-m telescope. HC3N(J = 24−23) was observed in nine galaxies with the 10-m Submillimeter Telescope (SMT).
Results. HC3N 2−1 is detected in three galaxies: IC 342, M 66, and NGC 660 (> 3σ). HC3N 24−23 is detected in three galaxies: IC 342, NGC 1068, and IC 694. These are the first measurements of HC3N 2−1 in a relatively large sample of external galaxies, although the detection rate is low. For the HC3N 2−1 non-detections, upper limits (2σ) are derived for each galaxy, and stacking the non-detections is attempted to recover the weak signal of HC3N. The stacked spectrum, however, does not show any significant signs of HC3N 2−1 emission. The results are also compared with other transitions of HC3N observed in galaxies.
Conclusions. The low detection rate of both transitions suggests low abundance of HC3N in galaxies, which is consistent with other observational studies. The comparison between HC3N and HCN or HCO+shows a large diversity in the ratios between HC3N and HCN or HCO+. More observations are needed to interpret the behavior of HC3N in different types of galaxies.
