Multiple HC$_3$N line observations towards 19 Galactic massive star-forming regions

TL;DR

This study observed multiple HC$_3$N lines in 19 Galactic massive star-forming regions, revealing temperature ranges, turbulence, and possible luminosity-line width relations, advancing understanding of dense core conditions.

Contribution

First comprehensive multi-line HC$_3$N observations across a sizable sample of massive star-forming regions, providing insights into their physical conditions and dynamics.

Findings

HC$_3$N lines detected in most sources except W44.

Inner regions exhibit larger line widths indicating more turbulence.

Possible cutoff in IR luminosity versus line width relation at 10^6 L_sun.

Abstract

We performed observations of the HC$_3$N (24-23, 17-16, 11-10, 8-7) lines towards a sample consisting of 19 Galactic massive star-forming regions with the Arizona Radio Observatory 12-m and Caltech Submillimeter Observatory 10.4-m telescopes. HC$_3$N (24-23, 17-16, 11-10, 8-7) lines were detected in sources except for W44, where only HC$_3$N (17-16, 11-10) were detected. Twelve of the nineteen sources showed probable line wing features. The excitation temperatures were estimated from the line ratio of HC$_3$N (24-23) to HC$_3$N (17-16) for 18 sources and are in the range 23-57 K. The line widths of higher-$J$ transitions are larger than lower-$J$ ones for most sources. This indicates that the inner dense warm regions have more violent turbulence or other motions (such as rotation) than outer regions in these sources. A possible cutoff tendency was found around $L_{\rm IR}$ $\sim$ 10$^{6}$ $L_\odot$ in the relation between $L_{\rm IR}$ and full width at half maximum line widths.