AI 中文总结
该研究利用FAST超深中性氢观测，在希克森致密星系群100附近探测到延伸约1百万秒差距的弥漫HI结构，其包含大量中性气体，可能源于潮汐碎片或气体吸积，为密集环境重子循环提供新组分。
AI 中文摘要
星系演化受其与周围环境交换气体能力的强烈影响，但对这些过程的直接观测限制仍然很少。利用五百米口径球面射电望远镜（FAST）的超深中性氢（HI）观测，我们在致密星系群HCG 100周围探测到一个延伸约1百万秒差距的弥漫HI结构，积分柱密度低至约8.6×10¹⁷厘米⁻²。该结构是有史以来观测到的最延伸且最低密度的发射中性气体系统之一。HI气体形成一个连贯的包层，将致密星系群与邻近星系连接起来，并在HCG 100周围显示出跨越约0.6百万秒差距的大规模连贯速度梯度。延伸结构包含约1.4×10¹⁰太阳质量的弥漫中性气体，这意味着高达约40%-50%的HI气体存在于星系之外。这样大的弥漫HI结构可能源于大规模潮汐碎片或来自周围宇宙网的气体吸积。我们的结果表明，大量弥漫中性气体储层可以在星系群周围的百万秒差距尺度上长期存在，为密集环境中的重子循环提供了一个前所未见的组成部分。
英文摘要
The evolution of galaxies is strongly influenced by their ability to exchange gas with their surroundings, yet direct observational constraints on these processes remain scarce. Using ultra-deep neutral hydrogen (HI) observations with the Five-hundred-meter Aperture Spherical Telescope (FAST), we detect a diffuse HI structure extending over $\sim$1 Mpc around the compact galaxy group HCG 100, with integrated column densities down to $\sim$$8.6\times10^{17}$ cm$^{-2}$. This structure is among the most extended and lowest-density neutral gas systems ever observed in emission. The HI gas forms a coherent envelope connecting the compact group to neighboring galaxies and shows a large-scale coherent velocity gradient around HCG 100 extending across $\sim$0.6 Mpc. The extended structure contains $\sim$$1.4\times10^{10}$ $M_\odot$ of diffuse neutral gas, implying that up to $\sim$40$-$50\% of the HI gas resides outside galaxies. Such a large diffuse HI structure may arise either from large-scale tidal debris or gas accretion from the surrounding cosmic web. Our results demonstrate that massive reservoirs of diffuse neutral gas can persist on megaparsec scales around galaxy groups for extended periods, providing a previously unseen component of baryon cycling in dense environments.
Comments11 pages, 6 figures, 1 table, and 2 appendices, accepted for publication in ApJL
Journal refThe Astrophysical Journal Letters,1007, 2 (2026)
