THE CHANGING FRACTIONS OF TYPE IA SUPERNOVA NUV–OPTICAL SUBCLASSES WITH REDSHIFT
THE CHANGING FRACTIONS OF TYPE IA SUPERNOVA NUV–OPTICAL SUBCLASSES WITH REDSHIFT
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DOI：
10.1088/0004-637x/803/1/20
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发表时间：
2014-08
期刊：
影响因子：
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通讯作者：
P. Milne;R. Foley;P. Brown;G. Narayan
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文献类型：
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作者：
P. Milne;R. Foley;P. Brown;G. Narayan
Ia型超新星（SNe Ia）在低红移的紫外（UV）和光学测光显示存在两个不同的颜色组，由NUV-红色和NUV-蓝色事件组成。颜色曲线的差异主要在于偏移量，NUV-蓝色u − v？>颜色曲线比NUV-红色曲线蓝0.4马格。对于用Swift观测的23个低红移超新星Ia的样本，NUV-红色组占主导地位的比例为2：1。我们比较了中高红移Ia型超新星的静止帧紫外/光学分光光度法与低红移Ia型超新星的紫外/光学分光光度法和哈勃空间望远镜分光光度法，发现在高红移处存在相同的两个色组，但以紫外-蓝色事件为主导。在每个红/蓝组中，我们没有检测到不同红移的任何颜色偏移，从而深入了解超新星Ia紫外发射如何随红移而演变。通过光谱比较SNe Ia具有相似的峰宽和相位，我们探索的波长范围内产生的UV/光学色差。我们发现，NUV-红色超新星（SNe）的喷出物速度比NUV-蓝色天体的喷出物速度平均大约12%。这种速度差异可以解释一些紫外/光学色差，但在平均光谱中看到的光谱特征的强度差异需要额外的解释。由于B − v？>略有不同，对于这些组的颜色，NUV-红色SNe将使用普通技术低估它们的消光。这反过来又导致低估了NUV-蓝色超新星Ia的光学光度，特别是对于高红移的宇宙学样本。如果不考虑这种效应，就会产生距离偏差，这种偏差会随着红移的增加而增加，并可能使宇宙学参数的测量产生明显的偏差。
Ultraviolet (UV) and optical photometry of Type Ia supernovae (SNe Ia) at low redshift have revealed the existence of two distinct color groups, composed of NUV-red and NUV-blue events. The color curves differ primarily by an offset, with the NUV-blue u − v ?> color curves bluer than the NUV-red curves by 0.4 mag. For a sample of 23 low-redshift SNe Ia observed with Swift, the NUV-red group dominates by a ratio of 2:1. We compare rest-frame UV/optical spectrophotometry of intermediate- and high-redshift SNe Ia with UVOT photometry and Hubble Space Telescope spectrophotometry of low-redshift SNe Ia, finding that the same two color groups exist at higher redshift, but with the NUV-blue events as the dominant group. Within each red/blue group, we do not detect any offset in color for different redshifts, providing insight into how SN Ia UV emission evolves with redshift. Through spectral comparisons of SNe Ia with similar peak width and phase, we explore the wavelength range that produces the UV/optical color differences. We show that the ejecta velocity of NUV-red supernovae (SNe) is larger than that of NUV-blue objects by roughly 12% on average. This velocity difference can explain some of the UV/optical color difference, but differences in the strengths of spectral features seen in mean spectra require additional explanation. Because of the slightly different b − v ?> colors for these groups, NUV-red SNe will have their extinction underestimated using common techniques. This, in turn, leads to underestimation of the optical luminosity of the NUV-blue SNe Ia, in particular, for the high-redshift cosmological sample. Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters.