Ia型超新星中 intervening 物质的窄吸收线。IV. Ia型超新星：钠I D线强度与外部物质及内在性质的关系
Narrow absorption lines from intervening material in supernovae. IV. Type Ia supernovae: Na I D line strength relating to external material and intrinsic properties
AI总结：
研究Ia型超新星中钠I D线强度与外部物质及内在性质的关系，揭示年轻群体具有更强的蓝移钠吸收，与观测角度有关。
摘要：
Ia型超新星（SNe Ia）是某些双星系统中的白矮星热核爆发。它们已被广泛研究，但其前身和爆炸机制仍不清楚。我们研究了大量SNe Ia，比较了其光谱中的窄星际吸收特征与各种光度学和光谱学超新星属性，以及环境特征。我们发现，年轻、恒星形成更多且更位于中心的SNe Ia的钠吸收显著更强，如预期的那样。然而，我们还显示，存在一种与环境无关的内在性质的强依赖性。事实上，我们发现有证据表明存在两个环境SNe Ia群体，一个老的和一个年轻的，当根据Si II喷射速度、星云速度、消光、E(B-V)和红化曲线RV将年轻群体分开时，年轻群体显示出显著不同的钠强度分布。通过SNe Ia的聚类，我们恢复了一个具有低消光和正常喷射速度的老群体，同时确认年轻群体可以分为一个高消光、高速度的SNe Ia群体，其蓝移钠吸收显著更强，以及一个低消光、正常速度的群体，其钠吸收较少。我们将这种中间物质与内在性质的关系解释为年轻SNe Ia群体，发生在年轻和恒星形成环境中，具有不对称辐射，与附近物质相互作用，其观测结果因此依赖于观测角度。最后，我们显示宇宙质量阶梯与这些群体一致。
英文摘要：
Type Ia supernovae (SNe Ia) are thermonuclear runaways of some white dwarfs in binary systems. They have been extensively studied, yet their progenitor and explosion mechanisms remain poorly understood. We study a large sample of SNe Ia comparing the narrow interstellar absorption features in their spectra with various photometric and spectroscopic supernova properties, as well as environmental characteristics. The sodium absorption is significantly stronger in younger, more star-forming and more centrally located SNe Ia, as expected. However, we also show that there is a relation with intrinsic properties that is independent of the environment. In fact, there is substantial evidence for two environmental SN Ia populations, an old and a young one, with the young population showing significantly different distributions of sodium strength when divided according to the Si II ejecta velocity, nebular velocity, extinction, E(B-V), and reddening curve, RV. Performing a clustering of the SNe Ia, we recover an old population of SNe with low extinction and normal ejecta velocity, while the young population can be indeed subdivided into a group of highly-extincted, high-velocity SNe Ia with much stronger blueshifted sodium absorption, and another of low-extincted, normal-velocity objects with little sodium absorption. We interpret this relation of intervening material with intrinsic properties as evidence for the young SN Ia population, occurring in young and star-forming environments, to have asymmetric radiation that interacts with nearby material, and whose observables depend thus on the viewing angle. Finally, we show that the cosmological mass-step is consistent with these populations.
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