LERMA/LRA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Université Paris 06, Ecole normale supérieure, 75005 Paris, France.
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany.
Nature. 2017 Aug 24;548(7668):430-433. doi: 10.1038/nature23298. Epub 2017 Aug 14.
Starburst galaxies at the peak of cosmic star formation are among the most extreme star-forming engines in the Universe, producing stars over about 100 million years (ref. 2). The star-formation rates of these galaxies, which exceed 100 solar masses per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Consequently, starburst galaxies are ideal for studying the interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH, is a most useful molecule for such studies because it cannot form in cold gas without suprathermal energy input, so its presence indicates dissipation of mechanical energy or strong ultraviolet irradiation. Here we report the detection of CH (J = 1-0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts near 2.5. This line has such a high critical density for excitation that it is emitted only in very dense gas, and is absorbed in low-density gas. We find that the CH emission lines, which are broader than 1,000 kilometres per second, originate in dense shock waves powered by hot galactic winds. The CH absorption lines reveal highly turbulent reservoirs of cool (about 100 kelvin), low-density gas, extending far (more than 10 kiloparsecs) outside the starburst galaxies (which have radii of less than 1 kiloparsec). We show that the galactic winds sustain turbulence in the 10-kiloparsec-scale environments of the galaxies, processing these environments into multiphase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star-formation rates. Another mass input is therefore required for these reservoirs, which could be provided by ongoing mergers or cold-stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase of a galaxy instead of quenching it.
处于宇宙恒星形成高峰期的爆发星系是宇宙中最极端的恒星形成引擎之一，在大约 1 亿年的时间里产生恒星（参考文献 2）。这些星系的恒星形成率超过每年 100 个太阳质量，需要将大量冷分子气体输送到其核心，尽管受到来自恒星或活动星系核的强烈反馈。因此，爆发星系是研究这种反馈与星系增长之间相互作用的理想选择。甲叉基阳离子 CH 是此类研究中最有用的分子，因为如果没有超热能量输入，它就不能在冷气体中形成，因此它的存在表明机械能的耗散或强烈的紫外辐射。在这里，我们报告了在六个近 2.5 红移的受透镜作用的爆发星系的光谱中检测到 CH（J=1-0）发射和吸收线。该线的激发临界密度非常高，因此仅在非常密集的气体中发射，并且在低密度气体中吸收。我们发现，CH 发射线的宽度超过 1000 公里/秒，源自由热星系风驱动的密集冲击波。CH 吸收线揭示了冷（约 100 开尔文）、低密度气体的高度湍流云，这些气体延伸到爆发星系（半径小于 1 千秒差距）之外很远的地方（超过 10 千秒差距）。我们表明，星系风在星系的 10 千秒差距尺度环境中维持湍流，将这些环境处理成多相、受引力束缚的云。然而，发现质量外流率不足以平衡恒星形成率。因此，这些储层需要另一个质量输入，这可能是由正在进行的合并或冷流吸积提供的。我们的结果表明，星系反馈与湍流和重力联合作用，延长了星系的爆发阶段，而不是使其熄灭。
