Pilot HI Survey of Planck Galactic Cold Clumps with FAST

Abstract

We present a pilot HI survey of 17 Planck Galactic Cold Clumps (PGCCs) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). HI Narrow Self-Absorption (HINSA) is an effective method to detect cold HI being mixed with molecular hydrogen H${}_2$ and improves our understanding of the atomic to molecular transition in the interstellar medium. HINSA was found in 58\% PGCCs that we observed. The column density of HINSA was found to have an intermediate correlation with that of ${}^{13}$CO, following $\log (\mathrm{N}(\mathrm{HINSA}))=(0.52\pm 0.26)\log ({\mathrm{N}}_{{}^{13}\mathrm{CO}})+(10\pm 4.1)$. HI abundance relative to total hydrogen [HI]/[H] has an average value of $4.4\times 10^{-3}$, which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds. For clouds with total column density N${}_{\mathrm{H}}>5\times 10^{20}$ cm${}^{-2}$, an inverse correlation between HINSA abundance and total hydrogen column density is found, confirming the depletion of cold HI gas during molecular gas formation in more massive clouds. Nonthermal line width of ${}^{13}$CO is about 0-0.5 km s${}^{-1}$ larger than that of HINSA. One possible explanation of narrower nonthermal width of HINSA is that HINSA region is smaller than that of ${}^{13}$CO. Based on an analytic model of H${}_2$ formation and H${}_2$ dissociation by cosmic ray, we found the cloud ages to be within 10${}^{6.7}$-10${}^{7.0}$ yr for five sources.

arXiv comment11 pages, 11 figures, accepted by the Research in Astronomy and Astrophysics (RAA)

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Cited by in corpus (6)

• Peering into the Milky Way by FAST: I. Exquisite HI structures in the inner Galactic disk from the piggyback line observations of the FAST GPPS survey
• OH Evolution in Molecular Clouds
• A FAST Survey of HINSA in PGCCs Guided by HC3N
• The CO-dark molecular gas in the cold HI arc
• HI Narrow-Line Self-Absorptions Toward the High-Mass Star-Forming Region G176.51+00.20
• Physical Properties and HI-to-H2 Transition Across Taurus Linear Edge