Network of velocity-coherent filaments formed by supersonic turbulence in a very-high-velocity HI cloud

• DOI: 10.48550/arxiv.2502.10897
• Publication Date: 2025-02-15
• Authors: Xunchuan Liu; Tie Liu; Pak Shing Li; Xiaofeng Mai; C. Henkel; P. F. Goldsmith; Sheng‐Li Qin; Yan Gong; Xing Lu; Fengwei Xu; Qiuyi Luo; Hongli Liu; Tianwei Zhang; Cheng Yu; Yupeng Di; Yuefang Wu; Qilao Gu; Ningyu Tang; A. Y. Yang; Zhiqiang Shen
• Keywords: Astrophysics - Solar and Stellar Astrophysics; Astrophysics of Galaxies (astro-ph.GA); FOS: Physical sciences; Astrophysics - Astrophysics of Galaxies; Solar and Stellar Astrophysics (astro-ph.SR)

The warm neutral medium (WNM) was thought to be subsonically/transonically turbulent, and it lacks a network of intertwined filaments that are commonly seen in both molecular clouds cold (CNM). Here, we report HI~21 cm line observations very-high-velocity (-330 km s$^{-1}$ $<V_{\rm LSR}<$ -250 s$^{-1}$) cloud (VHVC), using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) with unprecedented resolution sensitivity. For first time, such VHVC is clearly revealed supersonic WNM system consisting velocity-coherent HI~filaments. forms slim curves, hubs, webs, distributed different layers within position-position-velocity ({\it ppv}) data cube. entire has skewed log-normal probability distribution column density themselves show asymmetrical radial profiles, indicating shock compression by magnetohydrodynamic (MHD) turbulence, as also confirmed our MHD simulation (sonic Mach number $M_{\rm s}=3$ Alfv\'en A}=1$). This work suggests hierarchical can established shocks low-density WNM, where gravity negligible, offering viable pathway structure formation earliest evolutionary phases interstellar (ISM).