AI 中文总结
利用FAST在M51附近发现一对氢云，通过搜索、建模等方法研究其特性，与相关预测和模拟比较，识别出云S和云N，它们是有希望的RELHIC候选体，未来高分辨率观测对区分其性质至关重要。
AI 中文摘要
我们报告了利用500米口径球面射电望远镜（FAST）在M51（NGC 5194）附近发现了一对氢云。这些云没有光学对应体，是重电离限制氢云（RELHIC）的潜在候选体。我们使用SoFiA在深度FEASTS观测中搜索致密氢源，并通过与DESI遗产成像调查交叉匹配来去除有光学对应体的天体。将剩余候选体建模为嵌入纳瓦罗-弗伦克-怀特暗物质晕中的流体静力氢结构，并与RELHIC预测和TNG50模拟进行比较。我们在距M51投影距离70-90千秒差距处识别出两个氢云，云S和云N。每个云的氢质量约为10^6.5太阳质量，速度弥散约为20千米/秒，在g波段表面亮度极限约为27.5星等/平方角秒以下没有可探测的光学对应体。它们的恒星光度被限制在10^5太阳光度以下。它们的氢特性与RELHIC预测一致，对应宿主晕质量为3.7±0.4×10^9太阳质量。云S和云N是有希望但不确定的RELHIC候选体。在相互作用的M51系统中，潮汐起源仍然有可能，特别是因为这些云未被FAST分辨，且云N可能显示出速度梯度。未来的高分辨率干涉测量观测对于区分无恒星暗物质晕和潮汐碎片至关重要。
英文摘要
We report the discovery of a pair of H I clouds near M51 (NGC 5194) using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These clouds have no optical counterparts and are potential candidates for Reionization-Limited H I Clouds (RELHICs). We search for compact H I sources in deep FEASTS observations using SoFiA and remove objects with optical counterparts through cross-matching with the DESI Legacy Imaging Surveys. The remaining candidates are modelled as hydrostatic H I structures embedded in Navarro-Frenk-White dark matter haloes and compared with RELHIC predictions and TNG50 simulations. We identify two H I clouds, Cloud S and Cloud N, at projected distances of 70--90 kpc from M51. Each cloud has an H I mass of approximately 10^6.5 solar masses, a velocity dispersion of about 20 km/s, and no detectable optical counterpart down to a g-band surface brightness limit of approximately 27.5 mag arcsec^-2. Their stellar luminosities are constrained to be below 10^5 solar luminosities. Their H I properties are consistent with RELHIC predictions, corresponding to host halo masses of 3.7 +- 0.4 * 10^9 solar masses. Cloud S and Cloud N are promising but not definitive RELHIC candidates. A tidal origin remains possible in the interacting M51 system, especially because the clouds are unresolved by FAST and Cloud N may show a velocity gradient. Future high-resolution interferometric observations will be crucial for distinguishing between starless dark matter haloes and tidal debris.
Comments8 figures, 1 table, 8 pages; accepted for publication in Astronomy and Astrophysics
