Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A
Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A
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DOI：
10.1093/mnras/staa638
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发表时间：
2020-03
影响因子：
4.8
通讯作者：
G. Shaw;G. Ferland
中科院分区：
文献类型：
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作者：
G. Shaw;G. Ferland
伽玛射线暴（GRB）余辉为研究高红移恒星形成星系的星际介质（ISM）提供了一个独特的机会。GRB- dlas（阻尼Lyman- $\alpha$吸收剂）含有较大的中性氢柱密度N(H I)，并且可以在GRB余辉下观察到。大部分GRB-DLAs显示存在分子氢（H $_2$），这是恒星形成的一个指标。因此，研究具有H $_2$谱线的grb - dla对于破译和了解其物理状态具有重要意义。GRB-DLAs 121024A和120815A分别位于红移2.30和2.36，是两个重要的含H $_2$的GRB-DLAs。除了H $_2$外，这两个GRB-DLAs还显示了许多金属线。在这项工作中，我们对GRB-DLAs 121024A和120815A中的H $_2$线以及那些金属线进行了详细的数值研究。我们使用光谱合成代码CLOUDY进行这项研究。这种建模帮助我们确定产生这些线的潜在物理条件，从而比以往任何其他研究都更详细地了解这两个grb - dla。我们发现这两个含H $_2$的dla的氢密度为$\geq$ 60 cm $^{-3}$。此外，我们的研究推断，这两个grb - dla的线性尺寸为$\leq 17.7$ pc，平均气体温度在云厚度上的平均值为$\leq$ 140 K。
The gamma-ray burst (GRB) afterglows provide an unique opportunity to study the interstellar medium (ISM) of star-forming galaxies at high-redshift. The GRB-DLAs (damped Lyman-$\alpha$ absorbers) contain a large neutral hydrogen column density, N(H I), and are observed against the GRB afterglow. A large fraction of GRB-DLAs show presence of molecular hydrogen (H$_2$) which is an indicator of star-formation. Hence it is important to study those GRB-DLAs which have H$_2$ lines to decipher and understand their physical conditions. The GRB-DLAs 121024A and 120815A, situated at redshift 2.30 and 2.36 respectively, are two such important H$_2$-bearing GRB-DLAs. Besides H$_2$, these two GRB-DLAs also show many metal lines. In this work we have carried out a detail numerical study on the H$_2$ lines, as well as on those metal lines, in GRB-DLAs 121024A and 120815A self-consistently. We use the spectral synthesis code CLOUDY for this study. This modeling helps us to determine the underlying physical conditions which give rise such lines and hence to understand these two GRB-DLAs in much more detail than any other previous investigation. We find that the hydrogen densities for these two H$_2$-bearing DLAs are $\geq$ 60 cm$^{-3}$. Moreover our study infers that the linear sizes are $\leq 17.7$ pc for these two GRB-DLAs, and the mean gas temperatures averaged over the cloud thickness, are $\leq$ 140 K.