Shenglan Sun, Ke Wang, Xunchuan Liu and Fengwei Xu
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引用次数: 0
摘要
沿着银河旋臂运行的细长分子丝被称为 "骨骼",因为它们构成了银河的骨架。然而,它们的起源仍是一个未解之谜。在这里,我们将五百米孔径球面射电望远镜(FAST)拍摄的 HI 光谱图像与档案 CO 和 Herschel 尘埃辐射进行比较,以研究两个典型的银河骨架(CFG028.68-0.28 和 CFG047.06+0.26 )中 HI 向 H2 的转化。灵敏的 FAST HI 图像和改进的方法使我们能够提取出与丝状体上和丝状体外 CO 线发射相关的 HI 窄自吸收(HINSA)特征,首次揭示了 HINSA 在遥远云层中的普遍性。两块骨头的冷 HI 丰度[HI]/[H2]介于 ∼(0.5 到 44.7) × 10-3 之间,揭示了不同程度的 HI-H2 转换,与附近的低质量恒星形成云、普朗克银河系冷云团和附近活跃的高质量恒星形成区 G176.51+00.20 的情况相似。骨骼中的 HI-H2 转换已经持续了 2.2-13.2 Myr,这个时间尺度与其中大质量恒星形成的时间尺度相当。因此,我们正在目睹年轻的巨分子云(GMC)与快速的大质量恒星形成。我们的研究为在 FAST 时代利用 HINSA 研究银河系骨骼中的云形成,以及更广泛意义上的遥远巨分子云的形成铺平了道路。
The Formation of Milky Way “Bones”: Ubiquitous HI Narrow Self-absorption Associated with CO Emission
Long and skinny molecular filaments running along Galactic spiral arms are known as “bones,” since they make up the skeleton of the Milky Way. However, their origin is still an open question. Here, we compare spectral images of HI taken by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) with archival CO and Herschel dust emission to investigate the conversion from HI to H2 in two typical Galactic bones, CFG028.68-0.28 and CFG047.06+0.26. Sensitive FAST HI images and an improved methodology enabled us to extract HI narrow self-absorption (HINSA) features associated with CO line emission on and off the filaments, revealing the ubiquity of HINSA toward distant clouds for the first time. The derived cold HI abundances, [HI]/[H2], of the two bones range from ∼(0.5 to 44.7) × 10−3, which reveal different degrees of HI–H2 conversion, and are similar to those of nearby, low-mass star-forming clouds, Planck Galactic cold clumps, and a nearby active high-mass star-forming region G176.51+00.20. The HI–H2 conversion has been ongoing for 2.2–13.2 Myr in the bones, a timescale comparable to that of massive star formation therein. Therefore, we are witnessing young giant molecular clouds (GMCs) with rapid massive star formation. Our study paves the way of using HINSA to study cloud formation in Galactic bones and, more generally, in distant GMCs in the FAST era.