A FAST Survey of HINSA in PGCCs Guided by HC3N

TL;DR

This study uses FAST to detect HINSA in PGCCs, revealing high detection rates and insights into molecular distributions, with implications for understanding cold cloud structures.

Contribution

Introduces an improved HINSA extraction method and provides a comprehensive analysis of HINSA, HC3N, and CO in PGCCs, highlighting their spatial correlations and physical properties.

Findings

HINSA detected in 92% of PGCCs, including most with HC3N emission.

HINSA distribution aligns with CO emission, avoiding warm dust and stellar regions.

HI abundance in PGCCs is about 3E-4, with non-thermal velocities consistent across tracers.

Abstract

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we search for HI narrow-line self-absorption (HINSA) features in twelve Planck Galactic cold clumps (PGCCs), one starless core L1521B and four star forming sources. Eight of the 12 PGCCs have emission of J=2-1 of cyanoacetylene (HC3N). With an improved HINSA extraction method more robust for weaker and blended features with high velocity resolution, the detection rates of HINSA in PGCCCs are high, at 92% overall (11/12) and 87% (7/8) among sources with HC3N J=2-1 emissions. Combining the data of molecular spectra and Planck continuum maps, we studied the morphologies, abundances and excitations of HI, CO and HC3N in PGCCs. The distribution of HINSA is similar to that of CO emission. HINSA tends to be not detected in regions associated with warm dust and background ionizing radiation, as well as regions associated with stellar objects. The abundances of HI in PGCCs are approximately 3E-4, and vary within a factor of ~3. The non-thermal velocity dispersions traced by C18O J=1-0 and HINSA are consistent with each other (0.1-0.4 km/s), larger than those of HC3N (~0.1 km/s). Carbon chain molecule abundant PGCCs provide a good sample to study HINSA.