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Massive Star Formation Within The Leo 'primordial' Ring

机译：狮子座“原始”环内的大规模恒星形成

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Few intergalactic, plausibly primordial clouds of neutral atomic hydrogen (Hi) have been found in the local Universe, suggesting that such structures have either dispersed, become ionized or produced a stellar population on gigayear timescales. The Leo ring, a massive (M_(Hi) ≈ 1.8× 10~9M_☉, M_☉ denoting the solar mass), 200-kpc-wide structure orbiting the galaxies M105 and NGC 3384 with a 4-Gyr period, is a candidate primordial cloud. Despite repeated atttempts, it has previously been seen only from H i emission, suggesting the absence of a stellar population. Here we report the detection of ultraviolet light from gaseous substructures of the Leo ring, which we attribute to recent massive star formation. The ultraviolet colour of the detected complexes is blue, implying the onset of a burst of star formation or continuous star formation of moderate (～10~8-yr) duration. Measured ultraviolet-visible photometry favours models with low metallicity (Z≈ Z_☉/ 50-Z)☉/5, Z_☉ denoting the solar metallicity), that is, a low proportion of elements heavier than helium, although spectroscopic confirmation is needed. We speculate that the complexes are dwarf galaxies observed during their formation, but distinguished by their lack of a dark matter component5. In this regard, they resemble tidal dwarf galaxies, although without the enrichment preceding tidal stripping. If structures like the Leo ring were common in the early Universe, they may have produced a large, yet undetected, population of faint, metal-poor, halo-lacking dwarf galaxies.
机译：在当地宇宙中几乎没有发现星系间的，似乎是中性原子氢（Hi）的原始云，这表明这种结构在千兆年尺度上已经分散，电离或产生了恒星。狮子座环是一个巨大的行星（M_（Hi）≈1.8×10〜9M_☉，M_☉表示太阳质量），围绕星系M105和NGC 3384绕着4-Gyr周期旋转，时速为200 kpc。原始云。尽管反复尝试，但以前仅从H i发射中看到，表明没有恒星种群。在这里，我们报告了从狮子座环的气态亚结构中检测到紫外线的原因，这归因于最近的大规模恒星形成。所检测到的复合物的紫外线为蓝色，这意味着持续一定时间（约10至8年）的恒星爆发或连续恒星爆发。测得的紫外可见光度法偏爱金属性较低的模型（Z≈Z_☉/ 50-Z）☉/ 5，Z_☉表示太阳金属性），也就是说，尽管需要光谱确认，但比氦重的元素比例低。我们推测这些复合物是在形成过程中观察到的矮星系，但以缺乏暗物质成分为特征5。在这方面，它们类似于潮汐矮星系，尽管在潮汐剥离之前没有富集。如果像Leo环这样的结构在早期的宇宙中很常见，它们可能会产生大量但尚未发现的微弱，金属贫乏，无光晕的矮星系。

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