ZFIRE：用H $α$等效宽度研究z~2处的原位初始质量函数
ZFIRE: Using H$α$ equivalent widths to investigate the in situ initial mass function at z~2
摘要：
利用ZFIRE巡天（http：zfire.swinburne.edu.au），利用H-$α$等效宽度（H-$α$-EW）和静止坐标系光学色，研究了102个恒星形成星系的质量完备（log 10（M-$_*$/$_\odot$）~9.3）样本的初始质量函数（IMF）的高质量斜率.我们比较灰尘校正的H $α$ -EW分布与PEGASE.2和Starburst 99合成恒星星族模型的恒星形成历史（SFH）的预测。我们发现了一个过量的高H $α$ -EW星系是高达0.3- 0.5德克斯以上的模型预测的Salpeter IMF轨迹和H $α$ -EW分布是更广泛的（10- 500欧姆）比可以很容易地解释一个简单的单调SFH与标准的Salpeter斜率IMF。虽然当假设恒星和星云谱线之间没有相对衰减差异时，这种差异有所缓解，但结果对观测偏差是稳健的，并且没有单一的IMF（即非Salpeter斜率）可以重现数据。我们使用光谱叠加和蒙特卡罗模拟，星爆不能解释EW分布。我们调查其他的物理机制，包括模型的变化，恒星自转，双星演化，金属丰度，和国际货币基金组织的上质量截止。IMF的变化和/或高度旋转的极端贫金属星（Z~ 0.1 Z $_\odot$）与二元相互作用是我们的数据最合理的解释。如果IMF变化，则最高H $α$ -EW将需要非常浅的斜率（$Γ$ >-1.0），其中没有一个斜率能够再现数据。因此，国际货币基金组织将不得不随机变化。我们的结论是，恒星在z~2的人口显示出显着的差异，从本地人口，并没有简单的物理模型来解释大的变化在z~2的H $α$ -EWs。
英文摘要：
We use the ZFIRE survey (http://zfire.swinburne.edu.au) to investigate the high mass slope of the initial mass function (IMF) for a mass-complete (log10(M$_*$/M$_\odot$)~9.3) sample of 102 star-forming galaxies at z~2 using their H$α$ equivalent widths (H$α$-EW) and rest-frame optical colours. We compare dust-corrected H$α$-EW distributions with predictions of star-formation histories (SFH) from PEGASE.2 and Starburst99 synthetic stellar population models. We find an excess of high H$α$-EW galaxies that are up to 0.3--0.5 dex above the model-predicted Salpeter IMF locus and the H$α$-EW distribution is much broader (10--500 Å) than can easily be explained by a simple monotonic SFH with a standard Salpeter-slope IMF. Though this discrepancy is somewhat alleviated when it is assumed that there is no relative attenuation difference between stars and nebular lines, the result is robust against observational biases, and no single IMF (i.e. non-Salpeter slope) can reproduce the data. We show using both spectral stacking and Monte Carlo simulations that starbursts cannot explain the EW distribution. We investigate other physical mechanisms including models with variations in stellar rotation, binary star evolution, metallicity, and the IMF upper-mass cutoff. IMF variations and/or highly rotating extreme metal poor stars (Z~0.1Z$_\odot$) with binary interactions are the most plausible explanations for our data. If the IMF varies, then the highest H$α$-EWs would require very shallow slopes ($Γ$>-1.0) with no one slope able to reproduce the data. Thus, the IMF would have to vary stochastically. We conclude that the stellar populations at z~2 show distinct differences from local populations and there is no simple physical model to explain the large variation in H$α$-EWs at z~2.
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