Mixing metals in the early Universe
Mixing metals in the early Universe
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早期宇宙中的金属混合
DOI：
10.1046/j.1365-8711.2000.03857.x
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发表时间：
2000
影响因子：
4.8
通讯作者：
Y. Shchekinov
中科院分区：
文献类型：
--
作者：
A. Ferrara;M. Pettini;Y. Shchekinov
摘要：本文研究了星系际介质（IGM）金属丰度的演化，特别强调了其空间分布。我们认为金属富集是一个两步过程。首先，超新星（SN）爆炸将金属喷射到恒星形成星系周围相对较小的区域。通过对井喷的综合处理，我们发现SN本身不能将恒星核合成的产物分布到足够大的体积上，从而使整个IGM污染到所观察到的金属丰度水平。因此，必须调用另一种（但尚不清楚的）物理机制来混合金属，其尺度与最有效污染物星系之间的平均距离相当。从这个简单的假设中，我们得出了一些关于IGM金属丰度演化的可测试的预测。具体地说，我们发现：(i)在宇宙的恒星形成历史中，金属喷射的比例在z0约为50%；也就是说，今天大约有一半的金属是在IGM中发现的；（ii）如果喷射出的金属与宇宙中的重子均匀混合，则IGM的平均金属丰度为kZla V ej =Vb。1=25Z（在z3处）：然而，由于空间不均匀性，扩散区金属丰度分布的平均值在该值附近有一个宽的（超过2个数量级）的分布；（iii）如果金属在z & 1处分布更加均匀；如假设的那样，在z0处，IGM的金属丰度被狭窄地限制在Z < 0:1 ^ 0:03Z的范围内。最后，我们指出我们的结果可以解释观测到的簇内介质的金属含量。
ABSTRA C T We investigate the evolution of the metallicity of the intergalactic medium (IGM) with particular emphasis on its spatial distribution. We propose that metal enrichment occurs as a two-step process. First, supernova (SN) explosions eject metals into relatively small regions confined to the surroundings of star-forming galaxies. From a comprehensive treatment of blowout we show that SN by themselves fail by more than one order of magnitude to distribute the products of stellar nucleosynthesis over volumes large enough to pollute the whole IGM to the metallicity levels observed. Thus, an additional (but as yet unknown) physical mechanism must be invoked to mix the metals on scales comparable to the mean distance between the galaxies that are most efficient pollutants. From this simple hypothesis we derive a number of testable predictions for the evolution of the IGM metallicity. Specifically, we find that: (i) the fraction of metals ejected over the starformation history of the Universe is about 50 per cent at za 0; that is, approximately half of the metals today are found in the IGM; (ii) if the ejected metals were homogeneously mixed with the baryons in the Universe, the average IGM metallicity would be kZla V ej =Vb . 1=25Z( at za 3: However, due to spatial inhomogeneities, the mean of the distribution of metallicities in the diffusive zones has a wide (more than 2 orders of magnitude) spread around this value; (iii) if metals become more uniformly distributed at z & 1; as assumed, at za 0 the metallicity of the IGM is narrowly confined within the range Z < 0:1 ^ 0:03Z(: Finally, we point out that our results can account for the observed metal content of the intracluster medium.