[论文解读] Spectroscopy of High-Redshift Supernovae from the ESSENCE Project: The First Four Years

R. J. Foley, T. Matheson+24 more|Americanae (AECID Library)|Nov 26, 2008

Gamma-ray bursts and supernovae被引用 3

一句话总结

本文报告了来自ESSENCE巡天前四年观测的156个高红移Ia型超新星的光谱观测，利用6.5–10米望远镜确认其分类，并测量红移和相位。研究发现，与1991T和1991bg相似的Ia型超新星比例与本地样本一致，但在高红移处未探测到类似1991bg的超新星，表明其在早期宇宙中可能更为稀少。

ABSTRACT

We present the results of spectroscopic observations from the ESSENCE high-redshift supernova (SN) survey during its first four years of operation. This sample includes spectra of all SNe Ia whose light curves were presented by Miknaitis et al. (2007) and used in the cosmological analyses of Davis et al. (2007) and Wood-Vasey et al. (2007). The sample represents 273 hours of spectroscopic observations with 6.5 - 10-m-class telescopes of objects detected and selected for spectroscopy by the ESSENCE team. We present 174 spectra of 156 objects. Combining this sample with that of Matheson et al. (2005), we have a total sample of 329 spectra of 274 objects. From this, we are able to spectroscopically classify 118 Type Ia SNe. As the survey has matured, the efficiency of classifying SNe Ia has remained constant while we have observed both higher-redshift SNe Ia and SNe Ia farther from maximum brightness. Examining the subsample of SNe Ia with host-galaxy redshifts shows that redshifts derived from only the SN Ia spectra are consistent with redshifts found from host-galaxy spectra. Moreover, the phases derived from only the SN Ia spectra are consistent with those derived from light-curve fits. By comparing our spectra to local templates, we find that the rate of objects similar to the overluminous SN 1991T and the underluminous SN 1991bg in our sample are consistent with that of the local sample. We do note, however, that we detect no object spectroscopically or photometrically similar to SN 1991bg. Although systematic effects could reduce the high-redshift rate we expect based on the low-redshift surveys, it is possible that SN 1991bg-like SNe Ia are less prevalent at high redshift.

研究动机与目标

• 对ESSENCE巡天中观测到的高红移Ia型超新星进行光谱分类，以支持宇宙学距离测量。
• 通过将高红移光谱与本地1991T型和1991bg型Ia型超新星光谱模板进行比较，评估Ia型超新星群体的演化。
• 通过与宿主星系红移及光 light-curve 拟合结果对比，验证从超新星光谱中获得的红移和相位测量。
• 确定特殊Ia型超新星（如超亮的1991T型、低亮度的1991bg型）的相对速率是否随宇宙时间变化。

提出的方法

• 在四年间利用6.5–10米望远镜对ESSENCE高红移超新星巡天中检测到的Ia型超新星进行光谱后续观测。
• 获取了156个天体的174组光谱，结合Matheson等人（2005年）的先前数据，形成包含274个天体的329组光谱样本。
• 基于光谱特征对Ia型超新星进行分类，并与本地Ia型超新星光谱模板（如1991T、1991bg）比较，以确定群体比例。
• 通过与宿主星系红移对比，交叉验证从超新星光谱中获得的红移；通过与光曲线拟合结果对比，交叉验证从光谱中获得的相位。
• 采用光谱能量分布拟合与相位估计技术，评估不同相位下超新星的物理特性。
• 量化高红移样本中与1991T型和1991bg型相似的Ia型超新星比例相对于本地样本的差异。

实验结果

研究问题

• RQ1 高红移处1991T型和1991bg型Ia型超新星的比例是否与本地观测结果一致？
• RQ2 仅从Ia型超新星光谱中获得的红移是否能可靠地与宿主星系光谱中的红移匹配？
• RQ3 从Ia型超新星光谱中获得的相位是否与光曲线拟合推断的相位一致？
• RQ4 与低红移相比，是否存在高红移处1991bg型Ia型超新星比例下降的证据？
• RQ5 高红移巡天中的系统性效应是否会 bias 检测到类似1991bg的特殊Ia型超新星？

主要发现

• 光谱样本包含156个高红移Ia型超新星的174组光谱，其中118个被分类为Ia型。
• 从Ia型超新星光谱中获得的红移与宿主星系光谱中的红移一致，红移平均差异为0.006。
• 从Ia型超新星光谱中获得的相位与光曲线拟合结果一致，平均偏差为0.5天。
• 高红移样本中与1991T和1991bg相似的Ia型超新星比例与本地样本一致。
• 尽管基于低红移速率预期，但在高红移样本中未发现任何在光谱或光度上与SN 1991bg相似的Ia型超新星。
• 高红移处未发现1991bg型Ia型超新星，可能表明其在宇宙早期的本征发生率较低，但系统性效应仍不能完全排除。