Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK.
Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.
Nature. 2017 Apr 13;544(7649):202-206. doi: 10.1038/nature21677. Epub 2017 Mar 27.
Recent observations have revealed massive galactic molecular outflows that may have the physical conditions (high gas densities) required to form stars. Indeed, several recent models predict that such massive outflows may ignite star formation within the outflow itself. This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies, to the evolution in size and velocity dispersion of the spheroidal component of galaxies, and would contribute to the population of high-velocity stars, which could even escape the galaxy. Such star formation could provide in situ chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict it to contribute substantially to the star-formation rate observed in distant galaxies. Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star-formation rate in the outflow is larger than 15 solar masses per year. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics.
最近的观测结果揭示了大规模的星系分子外流，这些外流可能具有形成恒星所需的物理条件（高气体密度）。事实上，最近的几个模型预测，这种大规模的外流可能会在外流本身内部引发恒星形成。这种恒星形成模式，其中恒星以高速径向速度形成，可能会导致星系的形态演化，星系球型成分的大小和速度弥散的演化，并会促进高速恒星的形成，这些恒星甚至可能逃离星系。这种恒星形成可以为星系际和星系际介质提供原位化学增丰（通过大轨道上的年轻恒星的超新星爆炸），并且一些模型还预测它会对遥远星系中观测到的恒星形成率做出重大贡献。尽管存在由于气体压缩而导致外流或喷流进入宿主星系的恒星形成的观测证据，但仍缺乏在星系外流中发生恒星形成的确凿证据。在这里，我们报告了光谱观测结果，这些结果明确揭示了在红移为 0.0448 的星系外流中发生的恒星形成。推断出的外流中的恒星形成率大于每年 15 个太阳质量。其他星系外流中可能也发生了恒星形成，但由于缺乏足够的诊断方法，以前的观测可能错过了这些恒星形成。
