The fraction of ionizing radiation from massive stars that escapes to the intergalactic medium-猫眼课题宝

DOI：

10.1093/mnras/sty3460

发表时间：

2018-05

期刊：

Monthly Notices of the Royal Astronomical Society

影响因子：

4.8

通讯作者：

中科院分区：

物理与天体物理2区

文献类型：

作者：

N. Tanvir;J. Fynbo;A. D. U. Postigo;J. Japelj;K. Wiersema;K. Wiersema;D. Malesani;D. Perley;A. Levan;J. Selsing;S. B. Cenko;S. B. Cenko;D. A. Kann;B. Milvang-Jensen;E. Berger;Z. Cano;R. Chornock;S. Covino;A. Cucchiara;V. D’Elia;V. D’Elia;A. Gargiulo;P. Goldoni;A. Gomboc;K. Heintz;K. Heintz;J. Hjorth;L. Izzo;P. Jakobsson;L. Kaper;T. Krühler;T. Laskar;M. Myers;S. Piranomonte;G. Pugliese;A. Rossi;R. Sánchez-Ramírez;S. Schulze;M. Sparre;E. Stanway;G. Tagliaferri;C. Thöne;S. Vergani;P. Vreeswijk;R. Wijers;D. Watson;Dong Xu

恒星是否驱动了星系间介质的再电离，关键取决于从产生电离辐射的星系逃逸的电离辐射的比例。伽玛射线暴（GRB）余辉的光谱学可以用来估计极紫外（EUV）辐射沿着伽马射线暴的视线的不透明度。假设持续时间较长的伽马射线暴可以追踪到主导EUV产生的大质量恒星的位置，电离辐射的平均逸出率可以独立于星系大小或亮度计算出来。本文介绍了在1.6 < z < 6.7范围内140个grb的H - i柱密度（N - HI）测量结果的汇编。虽然样品是异质的，但在光谱分辨率和信噪比方面，对Ly α吸收线的拟合对N HI提供了强大的约束，即使对其他用途的质量不足的光谱也是如此。因此，我们在莱曼极限(fesc)≈0.005处建立了逃逸分数，98%的置信上限(fesc)≈0.015。这一分析表明，恒星对z < 5的电离辐射收支的贡献很小。在较高的红移下，可靠的结论受到GRB样本的小尺寸（7/140）的限制，但平均H柱密度的任何下降似乎都是适度的。我们还发现nhi与星系紫外光度或宿主恒星质量没有显著的相关性。我们详细讨论了潜在的偏差，并认为，尽管不可忽略，fesc的系统误差在任何方向上都不太可能超过一个因子~2，因此不会影响主要结论。考虑到许多GRB宿主都是金属丰度低、恒星形成率高的矮星系，这些结果对这些星系主导宇宙再电离的假设提出了一个特别的问题。©2018作者由牛津大学出版社代表皇家天文学会出版。

Whether stars could have driven the reionization of the intergalactic medium depends critically on the proportion of ionizing radiation that escapes the galaxies in which it is produced. Spectroscopy of gamma-ray burst (GRB) afterglows can be used to estimate the opacity to extreme ultraviolet (EUV) radiation along the lines-of-sight to the bursts. Assuming that long-duration GRBs trace the locations of the massive stars dominating EUV production, the average escape fraction of ionizing radiation can be calculated independently of galaxy size or luminosity. Here we present a compilation of H i column density (N HI ) measures for 140 GRBs in the range 1.6 < z < 6.7. Although the sample is heterogeneous, in terms of spectral resolution and signal-to-noise ratio, fits to the Ly α absorption line provide robust constraints on N HI , even for spectra of insufficient quality for other purposes. Thus we establish an escape fraction at the Lyman limit of (f esc ) ≈ 0.005, with a 98 per cent confidence upper limit of (f esc ) ≈ 0.015. This analysis suggests that stars provide a small contribution to the ionizing radiation budget at z < 5. At higher redshifts firm conclusions are limited by the small size of the GRB sample (7/140), but any decline in average H i column density seems to be modest. We also find no significant correlation of N HI with galaxy UV luminosity or host stellar mass. We discuss in some detail potential biases and argue that, while not negligible, systematic errors in f esc are unlikely to be more than a factor ~2 in either direction, and so would not affect the primary conclusions. Given that many GRB hosts are low-metallicity dwarf galaxies with high specific star-formation rates, these results present a particular problem for the hypothesis that such galaxies dominated the reionization of the Universe. © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.

The fraction of ionizing radiation from massive stars that escapes to the intergalactic medium

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