Lyman α line and continuum radiative transfer in a clumpy interstellar medium
Lyman α line and continuum radiative transfer in a clumpy interstellar medium
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块状星际介质中的莱曼α线和连续辐射传输
DOI：
10.1051/0004-6361/201220455
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发表时间：
2013
影响因子：
6.5
通讯作者：
P. Laursen
中科院分区：
文献类型：
--
作者：
F. Duval;D. Schaerer;G. Ostlin;P. Laursen
本论文主要研究恒星形成星系最强的光谱特征：氢原子的Lymanα复合线(以下简称LYA)。在恒星形成星系的远紫外光谱中，Lya线位于1215.67 A波长，是发现和研究宇宙早期遥远年轻恒星形成星系的重要示踪物和强大的发射线窗口。虽然Lya线本质上非常强，但它也是一条共振线。因此，LYA光子在恒星形成星系的星际介质(ISM)内的传输是非常复杂的，并取决于许多ISM量(HI质量、尘埃含量、HI气体运动学和ISM块度)。所有这些过程都严重影响了LYA谱线的出现特征(强度、等效宽度和谱线轮廓)，这些特征需要被理解，以确保正确解释所有在天体物理学和宇宙学中非常有前途的LYA定向研究。本论文的目的正是为了更深入地了解恒星形成星系中LYA谱线所经历的复杂的辐射输运。在这项工作中，我们对星系ISM中的LYA输运进行了数值和观测研究。在论文I和II中，我们进行了详细的数值研究，考察了块状ISM对LYA谱线强度和形状的影响。尽管到目前为止研究很少，但块状ISM对LYA的影响经常被用来解释从高红移星系观察到的异常强烈的LYA线的来源。一些分析研究表明，Lya光子的透过率确实高于块状ISM产生的UV连续谱光子，从而导致Lya等效宽度Ew(Lya)的增强。我们的结果表明，尽管笨拙有助于LYA的逃逸，但任何真正的ISM都不太可能导致EW(LYA)的任何增强。文中还讨论了其他可能的原因，从而得出结论：观测到的高EW(Lya)更有可能是由冷辐射或Lya辐射的各向异性逃逸产生的。这是一个雄心勃勃的观测计划，哈勃太空望远镜(HST)已经观测到了附近的14个恒星形成星系，目的是调查Lya是如何被输送出星系的，以及每个ISM量对Lya线产生了什么影响。论文III研究了单个星系的LYA性质和形态，而论文IV则详细研究了Mr k1486(样本中的第五个星系)令人惊讶的LYA发射线。
This thesis focuses on the intrinsically strongest spectral signature of star-forming galaxies: the Lyman alpha recombination line of the hydrogen atom (hereafter Lya). Located at the wavelength of 1215.67 A in the restframe far-ultraviolet spectra of star-forming galaxies, the Lya line proves to be a vital tracer and a powerful emission-line window to discover and to study the remote young star-forming galaxies of the early the Universe.Although intrinsically very strong, the Lya line is also a resonant line. As a consequence, the transport of Lya photons inside the interstellar medium (ISM) of star-forming galaxies is very complex and depends on many ISM quantities (HI mass, dust content, HI gas kinematics and ISM clumpiness). All this process has serious effects on the emergent features of the Lya line (strength, equivalent width and line profile) that need to be understood for ensuring a proper interpretation of all very promising Lya-oriented studies in astrophysics and cosmology. This is precisely the aim of this thesis to go deeper into our understanding of the complex radiative transport experienced by the Lya line in star-forming galaxies.In this work, we carry out both numerical and observational studies of Lya transport inside the ISM of galaxies.In Paper I and II, we perform detailed numerical studies that examine the effects of a clumpy ISM on the strength and the shape of the Lya line. Although poorly studied until now, the effects of a clumpy ISM on Lya have been routinely invoked to explain the origin of anomalously strong Lya line observed from high-redshift galaxies. Some analytical studies suggest indeed an higher transmission of Lya photons over UV continuum ones from clumpy ISMs, resulting in an enhanced Lya equivalent width EW(Lya). Our results show that although clumpiness facilitates the escape of Lya, it is highly unlikely that any real ISM should result in any enhancement of EW(Lya). Other possible causes are discussed in our papers, leading to the conclusion that the observed high EW(Lya) are more likely produced by cooling radiation or anisotropic escape of Lya radiation.Both Paper III and IV are related to the LARS project. This is an ambitious observational program in which 14 nearby star-forming galaxies have been observed with the Hubble Space Telescope (HST) with the aim to investigate how Lya is transported out of galaxies and what effects each ISM quantity produces on the Lya line. While Paper III examines the Lya properties and morphology of individual galaxies, Paper IV presents a detailed study of the surprising Lya emission line of Mrk1486 (the fifth galaxy of the sample).