We have discovered the stellar counterpart to the ALFALFA Virgo 7 cloud complex, which has been thought to be optically dark and nearly star-free since its discovery in 2007. This ∼190 kpc long chain of enormous atomic gas clouds (M _{H i} ∼ 10⁹ M _⊙) is embedded in the hot intracluster medium of the Virgo galaxy cluster but is isolated from any galaxy. Its faint, blue stellar counterpart, BC6, was identified in a visual search of archival optical and UV imaging. Follow-up observations with the Green Bank Telescope, Hobby–Eberly Telescope, and Hubble Space Telescope demonstrate that this faint counterpart is at the same velocity as the atomic gas, actively forming stars, and metal-rich (12 + (O/H) = 8.58 ± 0.25). We estimate its stellar mass to be only log(M*/M⊙)∼4.4 , making it one of the most gas-rich stellar systems known. Aside from its extraordinary gas content, the properties of BC6 are entirely consistent with those of a recently identified class of young, low-mass, isolated, and star-forming clouds in Virgo that appear to have formed via extreme ram pressure stripping events. We expand the existing discussion of the origin of this structure and suggest NGC 4522 as a likely candidate; however, the current evidence is not fully consistent with any of our proposed progenitor galaxies. We anticipate that other “dark” gas clouds in Virgo may have similarly faint, star-forming counterparts. We aim to identify these through the help of a citizen science search of the entire cluster.

中文翻译：

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黑暗不再：处女座星团中暗云的低光度恒星对应物* *基于霍比-埃伯利望远镜 (HET) 获得的观测结果，该望远镜是宾夕法尼亚州立大学奥斯汀分校德克萨斯大学的一个联合项目大学、慕尼黑路德维希马克西米利安大学和格奥尔格奥古斯特哥廷根大学。 HET 以其主要捐助者 William P. Hobby 和 Robert E. Eberly 的名字命名。

我们发现了 ALFALFA Virgo 7 云复合体的恒星对应物，自 2007 年发现以来，它一直被认为是光学黑暗的且几乎没有恒星。这个约 190 kpc 的巨大原子气体云长链（中号 _H我 ～ 10 ⁹ 中号 _⊙ ) 嵌入室女座星系团的热簇内介质中，但与任何星系隔离。它的微弱蓝色恒星对应物BC6是在对档案光学和紫外成像的目视搜索中发现的。绿岸望远镜、霍比-埃伯利望远镜和哈勃太空望远镜的后续观测表明，这个微弱的对应物与原子气体的速度相同，活跃地形成恒星，并且富含金属 (12 + (O/H) = 8.58 ± 0.25）。我们估计它的恒星质量仅为 日志(中号*/中号⊙）～4.4 ，使其成为已知气体最丰富的恒星系统之一。除了其非凡的气体含量之外，BC6 的性质与最近发现的室女座一类年轻、低质量、孤立的恒星形成云的性质完全一致，这些云似乎是通过极端冲压压力剥离事件形成的。我们扩展了对该结构起源的现有讨论，并建议 NGC 4522 作为可能的候选者；然而，目前的证据与我们提出的任何祖星系并不完全一致。我们预计处女座中的其他“暗”气体云可能也有类似的暗淡、恒星形成的对应物。我们的目标是通过对整个集群的公民科学搜索来识别这些。