On the variation of the initial mass function
On the variation of the initial mass function
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DOI：
10.1046/j.1365-8711.2001.04022.x
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发表时间：
2000-09
影响因子：
4.8
通讯作者：
P. Kroupa
中科院分区：
文献类型：
--
作者：
P. Kroupa
一个普遍的初始质量函数（IMF）是不直观的，但到目前为止，没有令人信服的证据，变量IMF存在。在恒星形成条件下探测IMF的系统变化将是星星形成的罗塞塔石碑。在这篇文章中，定义了一个平均的或银河场的IMF，强调只有两个质量的幂律指数变化的证据：0.5 M <$和0.08 M <$。使用这个假设的通用IMF，固有的不确定性，在任何观测估计的IMF的研究所引入的泊松噪声和星星集群的动力学演化的散射。结果发现，这种明显的分散再现相当不错的观察到的分散在幂律指数测定，从而定义的基本限制内，任何真正的变化变得无法检测。没有证据表明IMF是可变的，这意味着在经过充分研究的人群中，IMF的任何真实变化都必须小于这种离散度。幂律指数α的确定会受到系统误差的影响，这些误差主要来自于未分辨的二进制。系统偏差在这里被量化，结果是年轻星星的单星IMF在0.1到1 M <$之间比银河场IMF系统性地陡Δα <$0.5，银河场IMF平均由大约5-Gyr-old的恒星组成。球状星团中的MF平均而言似乎比银河场的MF系统地平坦（Piotto&Zoccali; Paresce & De Marchi），最近在银河晕中发现了古老的白矮星候选者，并且没有相关的低质量恒星（Ibata等人; Mendez & Minniti）提出了一个完全不同的IMF为这个古老的人口。因此，在金属丰度较高的环境中形成的星星似乎会产生相对较多的低质量恒星。虽然仍处于试验阶段，但这是一个有趣的趋势，与理论论证所预期的国际货币基金组织的系统性变化相一致。
A universal initial mass function (IMF) is not intuitive, but so far no convincing evidence for a variable IMF exists. The detection of systematic variations of the IMF with star-forming conditions would be the Rosetta Stone for star formation. In this contribution an average or Galactic-field IMF is defined, stressing that there is evidence for a change in the power-law index at only two masses: near 0.5 M⊙ and near 0.08 M⊙. Using this supposed universal IMF, the uncertainty inherent in any observational estimate of the IMF is investigated by studying the scatter introduced by Poisson noise and the dynamical evolution of star clusters. It is found that this apparent scatter reproduces quite well the observed scatter in power-law index determinations, thus defining the fundamental limit within which any true variation becomes undetectable. The absence of evidence for a variable IMF means that any true variation of the IMF in well-studied populations must be smaller than this scatter. Determinations of the power-law indices α are subject to systematic errors arising mostly from unresolved binaries. The systematic bias is quantified here, with the result that the single-star IMFs for young star clusters are systematically steeper by Δα≈0.5 between 0.1 and 1 M⊙ than the Galactic-field IMF, which is populated by, on average, about 5-Gyr-old stars. The MFs in globular clusters appear to be, on average, systematically flatter than the Galactic-field IMF (Piotto & Zoccali; Paresce & De Marchi), and the recent detection of ancient white-dwarf candidates in the Galactic halo and the absence of associated low-mass stars (Ibata et al.; Mendez & Minniti) suggest a radically different IMF for this ancient population. Star formation in higher metallicity environments thus appears to produce relatively more low-mass stars. While still tentative, this is an interesting trend, being consistent with a systematic variation of the IMF as expected from theoretical arguments.