从光谱模拟对z = 2-3恒星形成星系的恒星含量和物理条件的新认识
New insights into the stellar content and physical conditions of star-forming galaxies at z = 2-3 from spectral modelling
摘要：
我们已经使用了广泛的图书馆的模型和经验星系光谱（组装分别从人口合成代码的Bruzual和Charlot和斯隆数字巡天的第四次数据发布）来解释一些令人困惑的功能中看到的高红移恒星形成星系的光谱。我们表明，恒星He II 1640发射线，产生于扩张的大气中的Of和沃尔夫-拉叶星，应该是可检测到的等效宽度为0.5-1.5AA的综合光谱的恒星形成的星系，提供的金属丰度大于约一半的太阳。我们的模型再现了强度的He II 1640线测得的光谱莱曼break星系的金属丰度的既定值。随着更好的经验校准在本地星系，这一光谱特征有可能成为一个有用的诊断大质量恒星风在高，以及低，红移。我们还揭示了SDSS星系的[O III]/Hb与[N II]/Ha诊断图（BPT图）的位置之间的关系，以及它们相对于类似质量星系的超额比恒星形成率。我们推断，一个升高的电离参数U是在这种效果的根源，并提出，这也是高红移恒星形成星系的BPT图相比，本地的偏移的原因。我们进一步推测，更高的电子密度和逃逸分数的氢电离光子可能是负责系统的高值U在H II地区的高红移星系的因素。这种差异对强星云线丰度测定的影响被认为是相对较小的。
英文摘要：
We have used extensive libraries of model and empirical galaxy spectra (assembled respectively from the population synthesis code of Bruzual and Charlot and the fourth data release of the Sloan Digital Sky Survey) to interpret some puzzling features seen in the spectra of high redshift star-forming galaxies. We show that a stellar He II 1640 emission line, produced in the expanding atmospheres of Of and Wolf-Rayet stars, should be detectable with an equivalent width of 0.5-1.5AA in the integrated spectra of star-forming galaxies, provided the metallicity is greater than about half solar. Our models reproduce the strength of the He II 1640 line measured in the spectra of Lyman break galaxies for established values of their metallicities. With better empirical calibrations in local galaxies, this spectral feature has the potential of becoming a useful diagnostic of massive star winds at high, as well as low, redshifts. We also uncover a relationship in SDSS galaxies between their location in the [O III]/Hb vs. [N II]/Ha diagnostic diagram (the BPT diagram) and their excess specific star formation rate relative to galaxies of similar mass. We infer that an elevated ionisation parameter U is at the root of this effect, and propose that this is also the cause of the offset of high redshift star-forming galaxies in the BPT diagram compared to local ones. We further speculate that higher electron densities and escape fractions of hydrogen ionising photons may be the factors responsible for the systematically higher values of U in the H II regions of high redshift galaxies. The impact of such differences on abundance determinations from strong nebular lines are considered and found to be relatively minor.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
