Inefficient star formation in extremely metal poor galaxies
Inefficient star formation in extremely metal poor galaxies
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金属极度贫乏的星系中恒星形成效率低下
DOI：
10.1038/nature13820
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发表时间：
2014-10-16
期刊：
影响因子：
64.8
通讯作者：
Gu, Qiusheng
中科院分区：
文献类型：
--
作者：
Shi, Yong;Armus, Lee;Gu, Qiusheng
第一个星系包含由气体产生的恒星，几乎没有或没有“金属”（即比氦重的元素）。缺乏金属预计会抑制有效的气体冷却和恒星形成(1,2)，但在氧丰度（相对于氢）低于太阳十分之一的星系中尚未观察到这种效应(2-4)。附近金属极其贫乏的星系可能是我们最好的本地实验室，可以详细研究早期时期低金属丰度星系中普遍存在的条件。一氧化碳排放作为低金属丰度气体的示踪剂并不可靠(5-7)，虽然尘埃已被用来示踪低金属丰度星系中的气体(5,8-10)，但远红外的低空间分辨率通常会导致很大的不确定性(9,10)。在这里，我们报告了对两个氧丰度低于太阳值百分之十的星系的空间分辨红外观测，并表明这些星系中七个恒星形成团块中恒星的形成效率非常低。其效率还不到当今正常、富含金属的星系中发现的效率的十分之一，这表明早期宇宙中恒星的形成可能非常低效。
The first galaxies contain stars born out of gas with few or no 'metals' (that is, elements heavier than helium). The lack of metals is expected to inhibit efficient gas cooling and star formation(1,2), but this effect has yet to be observed in galaxies with an oxygen abundance (relative to hydrogen) below a tenth of that of the Sun(2-4). Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon monoxide emission is unreliable as a tracer of gas at low metallicities(5-7), and while dust has been used to trace gas in low-metallicity galaxies(5,8-10), low spatial resolution in the far-infrared has typically led to large uncertainties(9,10). Here we report spatially resolved infrared observations of two galaxies with oxygen abundances below ten per cent of the solar value, and show that stars formed very inefficiently in seven star-forming clumps in these galaxies. The efficiencies are less than a tenth of those found in normal, metal rich galaxies today, suggesting that star formation may have been very inefficient in the early Universe.