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arXiv 1807.09307astro-ph.GA
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用MUSE观测的极贫金属星系SBS0335-052E中扩展的HeII $λ$ 4686辐射

The extended HeII$λ$4686 emission in the extremely metal-poor galaxy SBS0335-052E seen with MUSE

C. Kehrig, J. M. Vilchez, M. A. Guerrero, J. Iglesias-Paramo, L. K. Hunt, S. Duarte Puertas, G. Ramos-Larios

摘要:

利用VLT/MUSE光谱和Chandra X射线观测,研究了近宇宙中最贫金属(Z ~ 3-4% Z $_{\odot}$)的HeII星暴SBS 0335 - 052 E。我们空间解析了星云HeII $λ$ 4686发射的光谱图,从中我们首次推导出了SBS 0335 - 052 E的总HeII电离能量预算。星云中的HeII谱线表示光子能量> 4 Ryd的相当硬的电离谱,并且在高z处比局部更常见。我们的研究排除了一个显着的贡献,从X射线源和冲击的HeII光电离预算,表明He $^{+}$激发主要是由于热恒星连续。我们发现了一个新的WR结,但我们也放弃了单个WR星作为HeII电离的主要负责人。通过与现有模型的比较,我们发现SBS 0335 - 052 E的HeII电离预算只能由单个旋转的无金属恒星或Z ~ 10 $^{-5}$和“头重脚轻”IMF的双星产生。这类恒星的金属丰度与SBS 0335 - 052 E中HII区域的金属丰度之间的差异与Kehrig等人(2015年)对非常缺乏金属的HeII发射星系IZw 18获得的结果相似。这些结果表明,HeII电离仍然超出了最先进的模型的能力。局部宇宙中极贫金属、高电离的星暴,如SBS 0335 - 052 E,为详细探索再电离时代可能存在的极端条件提供了独特的实验室。

英文摘要:

SBS0335-052E, one of the most metal-poor (Z ~ 3-4% Z$_{\odot}$) HeII-emitter starbursts known in the nearby universe, is studied using optical VLT/MUSE spectroscopic and Chandra X-ray observations. We spatially resolved the spectral map of the nebular HeII$λ$4686 emission from which we derived for the first time the total HeII-ionizing energy budget of SBS0335-052E. The nebular HeII line is indicative of a quite hard ionizing spectrum with photon energies > 4 Ryd, and is observed to be more common at high-z than locally. Our study rules out a significant contribution from X-ray sources and shocks to the HeII photoionization budget, indicating that the He$^{+}$ excitation is mainly due to hot stellar continua. We discovered a new WR knot, but we also discard single WR stars as the main responsible for the HeII ionization. By comparing observations with current models, we found that the HeII-ionization budget of SBS0335-052E can only be produced by either single, rotating metal-free stars or a binary population with Z ~ 10$^{-5}$ and a 'top-heavy' IMF. This discrepancy between the metallicity of such stars and that of the HII regions in SBS0335-052E is similar to results obtained by Kehrig et al. (2015) for the very metal-deficient HeII-emitting galaxy IZw18. These results suggest that the HeII ionization is still beyond the capabilities of state-of-the-art models. Extremely metal-poor, high-ionizing starbursts in the local universe, like SBS0335-052E, provide unique laboratories for exploring in detail the extreme conditions likely prevailing in the reionization era.

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