Probing cosmic chemical evolution with gamma-ray bursts: GRB 060206 at z = 4.048
Probing cosmic chemical evolution with gamma-ray bursts: GRB 060206 at z = 4.048
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DOI：
10.1051/0004-6361:20065056
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发表时间：
2006-02
影响因子：
6.5
通讯作者：
J. Fynbo;R. Starling;C. Ledoux;K. Wiersema;C. Thone;J. Sollerman;P. Jakobsson;J. Hjorth;D. Watson;P. Vreeswijk;P. Møller;E. Rol;J. Gorosabel;J. Naranen;R. Wijers;G. Bjornsson;J. M. C. Cer'on;P. Curran;D. Hartmann;S. Holland;B. Jensen;A. Levan;M. Limousin;C. Kouveliotou;G. Nelemans;K. Pedersen;R. Priddey;N. Tanvir
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文献类型：
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作者：
J. Fynbo;R. Starling;C. Ledoux;K. Wiersema;C. Thone;J. Sollerman;P. Jakobsson;J. Hjorth;D. Watson;P. Vreeswijk;P. Møller;E. Rol;J. Gorosabel;J. Naranen;R. Wijers;G. Bjornsson;J. M. C. Cer'on;P. Curran;D. Hartmann;S. Holland;B. Jensen;A. Levan;M. Limousin;C. Kouveliotou;G. Nelemans;K. Pedersen;R. Priddey;N. Tanvir
我们提出了早期的伽玛射线暴GRB 060206余辉的光谱学，目的是确定伽玛射线暴吸收体的金属丰度和周围暴介质的物理条件。我们还讨论了伽玛暴如何成为宇宙化学演化的重要补充探针。方法：伽玛暴余辉光谱的吸收线研究。结果：我们确定伽玛暴的红移为z=4.04795±0.00020。基于从阻尼莱曼α线测量中性氢柱密度和从弱的不饱和S II线测量金属含量，我们得出金属丰度[S/H]=-0.84 0. 10。这是从z~4处的吸收线测量的最高金属丰度之一。从非常高的列密度为禁止Si II*，O I*，和O I** 线，我们推断非常高的密度和系统中的低温。有证据表明存在log N（H_2）~17.0的H2分子，转化为log{f} ≥ 3.5的分子分数，f=2N（H2）/（2N（H2）+ N（H I））。即使伽玛暴只是由金属丰度低于~0.3 Zo的单个大质量恒星形成的，它们仍然可以是z>2时大部分星星形成的相当公正的示踪剂。因此，金属丰度的推导为GRB 060206在这里的一个完整的样本的GRB余辉将直接显示的金属丰度分布的代表性恒星形成星系在这些红移。
Aims.We present early optical spectroscopy of the afterglow of the gamma-ray burst GRB 060206 with the aim of determining the metallicity of the GRB absorber and the physical conditions in the circumburst medium. We also discuss how GRBs may be important complementary probes of cosmic chemical evolution. Methods.Absorption line study of the GRB afterglow spectrum. Results.We determine the redshift of the GRB to be z=4.04795±0.00020. Based on the measurement of the neutral hydrogen column density from the damped Lyman-alpha line and the metal content from weak, unsaturated S II lines we derive a metallicity of [S/H]=-0.84±0.10. This is one of the highest metallicities measured from absorption lines at z~4. From the very high column densities for the forbidden Si II*, O I*, and O I** lines we infer very high densities and low temperatures in the system. There is evidence for the presence of H2 molecules with log N(H_2)~17.0, translating into a molecular fraction of log{f}≈ -3.5 with f=2N(H2)/(2N(H2) + N(H I)). Even if GRBs are only formed by single massive stars with metallicities below ~0.3 Zo, they could still be fairly unbiased tracers of the bulk of the star formation at z>2. Hence, metallicities as derived for GRB 060206 here for a complete sample of GRB afterglows will directly show the distribution of metallicities for representative star-forming galaxies at these redshifts.