用GRB余辉光谱研究z=0.1 ~ 6.7恒星形成区的消光曲线
The extinction curves of star-forming regions from z=0.1 to 6.7 using GRB afterglow spectroscopy
摘要：
由于伽玛暴余辉的亮度、简单的幂律谱和遥远的恒星形成星系中伽玛暴的出现，它非常适合于消光研究。在本文中，我们提出了从41个样本的伽玛暴余辉，从X射线到近红外波长的SED分析结果。这是本星系群之外最大的消光曲线样本，也是迄今为止唯一一个基于光谱学的绝对消光曲线样本。视觉消光与HI柱密度以及总和气相金属柱密度的相关性进行了研究。大约一半的样品需要在光学和X射线区域之间的冷却中断。打破幂律的SED显示出delta_beta=0.51的光谱指数的平均变化，标准差为0.02。这与简单同步加速器模型的预期一致。在样品中，63%被SMC型消光曲线很好地描述，并且具有中等或低消光，AV<0.65。我们的样本中几乎有四分之一与无显著灭绝一致（通常AV<0.1）。在7%的样品（3个）中明确检测到2175 AA消光凸点，它们的A_V都大于1.0。我们发现，气尘比和金属丰度之间的反相关性与当地集团的关系。我们从软X射线吸收中得出的金属与尘埃的比值总是大于（3-30倍）本地群值，这可能意味着GRB宿主在将其金属转化为尘埃方面的效率可能较低。然而，我们发现，气体，尘埃和金属柱密度都可能受到光电离和尘埃破坏效应的伽玛射线暴。[删节]
英文摘要：
GRB afterglows are well suited to extinction studies due to their brightness, simple power-law spectra and the occurrence of GRBs in distant star forming galaxies. In this paper we present results from the SED analysis of a sample of 41 GRB afterglows, from X-ray to NIR wavelengths. This is the largest sample of extinction curves outside the Local Group and, to date, the only extragalactic sample of absolute extinction curves based on spectroscopy. Visual extinction correlation with HI column density as well as total and gas-phase metal column density are examined. Approximately half the sample require a cooling break between the optical and X-ray regimes. The broken power-law SEDs show an average change in the spectral index of delta_beta=0.51 with a standard deviation of 0.02. This is consistent with the expectation from a simple synchrotron model. Of the sample, 63% are well described by the SMC-type extinction curve and have moderate or low extinction, with AV<0.65. Almost a quarter of our sample is consistent with no significant extinction (typically AV<0.1). The 2175AA extinction bump is detected unequivocally in 7% of our sample (3 GRBs), which all have A_V>1.0. We find an anti-correlation between gas-to-dust ratio and metallicity consistent with the Local Group relation. Our metals-to-dust ratios derived from the soft X-ray absorption are always larger (3-30 times) than the Local Group value, which may mean that GRB hosts may be less efficient at turning their metals into dust. However, we find that gas, dust, and metal column densities are all likely to be influenced by photo-ionization and dust destruction effects from the GRB. [abridged]
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