Department of Physics, West Virginia University, PO Box 6315, Morgantown, West Virginia 26506, USA.
Nature. 2013 May 9;497(7448):224-6. doi: 10.1038/nature12082.
Spiral galaxies must acquire gas to maintain their observed level of star formation beyond the next few billion years. A source of this material may be the gas that resides between galaxies, but our understanding of the state and distribution of this gas is incomplete. Radio observations of the Local Group of galaxies have revealed hydrogen gas extending from the disk of the galaxy M31 at least halfway to M33. This feature has been interpreted to be the neutral component of a condensing intergalactic filament, which would be able to fuel star formation in M31 and M33, but simulations suggest that such a feature could also result from an interaction between both galaxies within the past few billion years (ref. 5). Here we report radio observations showing that about 50 per cent of this gas is composed of clouds, with the rest distributed in an extended, diffuse component. The clouds have velocities comparable to those of M31 and M33, and have properties suggesting that they are unrelated to other Local Group objects. We conclude that the clouds are likely to be transient condensations of gas embedded in an intergalactic filament and are therefore a potential source of fuel for future star formation in M31 and M33.
螺旋星系必须获得气体才能维持其在未来数十亿年内观测到的恒星形成水平。这种物质的来源可能是星系之间存在的气体，但我们对这种气体的状态和分布的理解并不完整。对本星系群中星系的无线电观测揭示了氢气体从星系 M31 的盘面延伸出去，至少在到 M33 的一半距离处。这一特征被解释为正在凝结的星系际纤维状结构的中性成分，这将能够为 M31 和 M33 中的恒星形成提供燃料，但模拟表明，这种特征也可能是由于过去数十亿年内两个星系之间的相互作用所致（参考文献 5）。在这里，我们报告了无线电观测结果，表明这种气体约有 50%由云团组成，其余部分分布在扩展的弥散成分中。这些云团的速度与 M31 和 M33 的速度相当，并且具有表明它们与本星系群其他物体无关的特性。我们的结论是，这些云团很可能是嵌入在星系际纤维状结构中的气体的瞬态凝结物，因此是 M31 和 M33 未来恒星形成的潜在燃料来源。
