标题： FAST对Planck银河系冷团块的试点HI调查 显示英文标题

标题： Pilot HI Survey of Planck Galactic Cold Clumps with FAST

摘要： 我们使用五百米口径球面射电望远镜（FAST）对17个普朗克银河系冷团（PGCCs）进行了HI试点调查。HI窄自吸收（HINSA）是一种有效检测与分子氢H$_2$混合的冷HI的方法，并提高了我们对星际介质中原子到分子转变的理解。在我们观测的PGCCs中，58\%发现了HINSA。HINSA的柱密度与$^{13}$CO的柱密度有中间相关性，遵循$\rm log( N(HINSA)) = (0.52\pm 0.26) log(N_{^{13}CO}) + (10 \pm 4.1) $。相对于总氢[H]/[H]的HI丰度平均值为$4.4\times 10^{-3}$，大约是之前对分子云HINSA调查平均值的2.8倍。对于总柱密度N$\rm_H >5 \times 10^{20}$ cm$^{-2}$的云，发现HINSA丰度与总氢柱密度呈反比关系，证实了在更大量分子气体形成的云中冷HI气体的消耗。 非热线宽的 $^{13}$CO 比 HINSA 大约 0-0.5 km s$^{-1}$。HINSA 非热线宽较窄的一个可能解释是 HINSA 区域比 $^{13}$CO 的区域小。基于宇宙射线形成和 H$_2$电离 H$_2$的分析模型，我们发现五个源的云团年龄在 10$^{6.7}$-10$^{7.0}$年之间。 显示英文摘要

摘要： 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 $\rm log( N(HINSA)) = (0.52\pm 0.26) log(N_{^{13}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$\rm_H >5 \times 10^{20}$ 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.