过去9千兆年Ia型超新星的平均光谱
The Mean Type Ia Supernova Spectrum Over the Past 9 Gigayears
摘要：
我们研究了在0<z<1.3的红移范围内采样的Ia型超新星（SNe Ia）的平均静止坐标系紫外（UV; <4500 A）光谱随红移演化的可能性。我们发现新的证据减少与红移的强度的中间质量元素（IME）的功能，特别是硅II和在较小程度上钙II“H&K”和镁II的混合物，表明较低的IME丰度在较高的红移SNE。更大部分的发光，更宽的光变曲线宽度（更高的“拉伸”）的超新星Ia预计在更高的红移比本地，所以我们比较我们观察到的光谱演化与预测的红移演变的拉伸分布（豪厄尔等2007年）结合拉伸依赖的超新星Ia光谱。我们表明，这个简单的模型可以复制的意义上的光谱演化，虽然最高的红移事件似乎另外缺乏硅和钙。我们还研究了平均超新星Ia紫外光学颜色作为红移的函数，被认为是敏感的祖先组成的变化。我们发现，预期的拉伸变化足以解释的差异，虽然在z~0的改进数据将使更精确的测试。因此，尽可能与现有的数据集，我们的研究结果支持继续使用SNe Ia作为标准化蜡烛。
英文摘要：
We examine the possibility of evolution with redshift in the mean rest-frame ultraviolet (UV; <4500A) spectrum of Type Ia Supernovae (SNe Ia) sampling the redshift range 0<z<1.3. We find new evidence for a decrease with redshift in the strength of intermediate-mass element (IME) features, particularly Si II and to a lesser extent Ca II "H&K" and Mg II blends, indicating lower IME abundances in the higher redshift SNe. A larger fraction of luminous, wider light-curve width (higher "stretch") SNe Ia are expected at higher redshift than locally, so we compare our observed spectral evolution with that predicted by a redshift-evolving stretch distribution (Howell et al. 2007) coupled with a stretch-dependent SN Ia spectrum. We show that the sense of the spectral evolution can be reproduced by this simple model, though the highest redshift events seem additionally deficient in Si and Ca. We also examine the mean SN Ia UV-optical colors as a function of redshift, thought to be sensitive to variations in progenitor composition. We find that the expected stretch variations are sufficient to explain the differences, although improved data at z~0 will enable more precise tests. Thus, to the extent possible with the available datasets, our results support the continued use of SNe Ia as standardized candles.
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