不同喷出物速度Ia型超新星的距离偏差
A Possible Distance Bias for Type Ia Supernovae with Different Ejecta Velocities
摘要：
在校正了它们的光变曲线形状和颜色之后，Ia型超新星（SNe Ia）是精确的宇宙学距离指示器。然而，在测量的距离和从宇宙学模型推断的距离之间的差异中仍然存在非零的固有散射（即，哈勃残差或HRs），表明SN Ia距离可以进一步改善。我们使用开源的关系数据库kaepora生成复合光谱所需的平均性能的相位，光变曲线的形状，和HR. At许多阶段，复合光谱从两个子样品的正负平均HRs显着不同。特别是，在峰值亮度前9天到峰值亮度后15天的所有光谱中，我们发现具有负HR的SNe平均比具有正HR的SNe具有更高的喷出物速度（几乎在所有光谱特征中都可以看出）。在相对于B波段最大值的+4天，使用62个超新星Ia样本，我们测量到超新星与Si II 6355线速度之间的0.091 +/- 0.035等HR阶跃高于/低于-11，000 km/s（中值速度）。经过光变曲线形状和颜色校正后，相对于宇宙学模型，具有较高速度的SNe往往会低估距离模量。在我们的样品中的本征散射在进行这种校正后从0.094 mag减小到0.082 mag。利用115 SNe Ia的Si II 6355速度演化，我们估计在99.4%的置信度下，正HR和负HR样本之间在每个历元存在> 500 km/s的速度差。最后，在晚于+37天的时期，我们观察到，负HR复合光谱往往具有较弱的光谱特征相比，正HR复合光谱。
英文摘要：
After correcting for their light-curve shape and color, Type Ia supernovae (SNe Ia) are precise cosmological distance indicators. However, there remains a non-zero intrinsic scatter in the differences between measured distance and that inferred from a cosmological model (i.e., Hubble residuals or HRs), indicating that SN Ia distances can potentially be further improved. We use the open-source relational database kaepora to generate composite spectra with desired average properties of phase, light-curve shape, and HR. At many phases, the composite spectra from two subsamples with positive and negative average HRs are significantly different. In particular, in all spectra from 9 days before to 15 days after peak brightness, we find that SNe with negative HRs have, on average, higher ejecta velocities (as seen in nearly every optical spectral feature) than SNe with positive HRs. At +4 days relative to B-band maximum, using a sample of 62 SNe Ia, we measure a 0.091 +/- 0.035 mag HR step between SNe with Si II 6355 line velocities higher/lower than -11,000 km/s (the median velocity). After light-curve shape and color correction, SNe with higher velocities tend to have underestimated distance moduli relative to a cosmological model. The intrinsic scatter in our sample reduces from 0.094 mag to 0.082 mag after making this correction. Using the Si II 6355 velocity evolution of 115 SNe Ia, we estimate that a velocity difference > 500 km/s exists at each epoch between the positive-HR and negative-HR samples with 99.4% confidence. Finally at epochs later than +37 days, we observe that negative-HR composite spectra tend to have weaker spectral features in comparison to positive-HR composite spectra.
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