舔指数纠缠与星系中恒星星族的有偏诊断
Lick-index entanglement and biased diagnostic of stellar populations in galaxies
摘要：
舔指数分光光度系统的内在统计和业务性质进行了研究，以方便更适当地用于天体物理研究。指数标准化过程中的非高斯效应表明，光谱数据必须达到最小S/N比，例如光谱分辨率R~2000时S/N >= 5 px^{-1}。此外，指数（重新）定义在窄带“颜色”方面应优于经典的伪等效宽度方案。不同折射率之间的重叠波长范围也是一个问题，因为它可能导致后者相互关联，超出任何严格的物理关系。嵌套配置的Fe 5335，Fe 5270指数，和所谓的“镁复合物”（包括Mg 1，Mg 2和Mgb）进行了分析，在这种情况下，通过评估隐含的偏见时，加入纠缠功能到“全球”诊断元指数，如仔细阅读[MgFe]金属丰度示踪剂。考虑了[OIII]（5007）和[NI]（5199）禁放气体发射对Fe 5015和Mgb吸收特征的扰动效应，提出了以[OIII]（5007）作为评价Hbeta剩余发射的代用指标时的修正方案。当应用于现今的椭圆星系人口时，修订后的Hbeta标度平均导致20-30%的年轻年龄估计。最后，误导性的作用，命名元素舔为基础的化学分析说明了惊人的情况下，Fe 4531。事实上，虽然铁名义上是高分辨率光谱中观察到的特征的主要贡献者，但我们已经表明，Fe 4531指数实际上最大化了其对钛丰度的响应。
英文摘要：
The Lick-index spectrophotometric system is investigated in its inherent statistical and operational properties to ease a more appropriate use for astrophysical studies. Non-Gaussian effects in the index standardization procedure suggest that a minimum S/N ratio has to be reached by spectral data, such as S/N >= 5 px^{-1} for a spectral resolution R~2000. In addition, index (re-)definition in terms of narrow-band "color" should be preferred over the classical pseudo-equivalent width scheme. The overlapping wavelength range among different indices is also an issue, as it may lead the latter ones to correlate, beyond any strictly physical relationship. The nested configuration of the Fe5335, Fe5270 indices, and the so-called "Mg complex" (including Mg1, Mg2 and Mgb) is analysed, in this context, by assessing the implied bias when joining entangled features into "global" diagnostic meta-indices, like the perused [MgFe] metallicity tracer. The perturbing effect of [OIII](5007) and [NI](5199) forbidden gas emission on Fe5015 and Mgb absorption features is considered, and an updated correction scheme is proposed when using [OIII](5007) as a proxy to appraise Hbeta residual emission. When applied to present-day elliptical galaxy population, the revised Hbeta scale leads, on average, to 20-30% younger age estimates. Finally, the misleading role of the christening element in Lick-based chemical analyses is illustrated for the striking case of Fe4531. In fact, while Iron is nominally the main contributor to the observed feature in high-resolution spectra, we have shown that the Fe4531 index actually maximizes its responsiveness to Titanium abundance.
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