Lyman Alpha Emitting Galaxies in the Nearby Universe
Lyman Alpha Emitting Galaxies in the Nearby Universe
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DOI：
10.1017/pasa.2015.25
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发表时间：
2015-05
影响因子：
6.3
通讯作者：
M. Hayes
中科院分区：
文献类型：
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作者：
M. Hayes
中性氢（Hi）的莱曼α发射线（Lyα）是天体物理星云光谱中最亮的发射特征，是观测星系的一个很有吸引力的观测特征。此外，作为一条紫外共振线，Lyα具有一些独特的特性，使其有助于研究星际介质和电离恒星在所有宇宙时代的性质。在这篇综述中，我提出了一个总结Lyα观测星系在附近的宇宙。通过紫外连续谱选择，在现有设备可达到的星等下，只有15%的本地星系群显示出超过20 μ m的Lyα等效宽度（WLyα）。这一比例在更高的红移下急剧增加，但只有在局部宇宙中，我们才能详细研究星系并组装前所未有的多波长数据集。我讨论了许多局部Lyα观测，表明当星系显示净Lyα发射时，它们普遍也会产生大尺度的散射Lyα晕，这主导了积分光度。关于全局测量，我们讨论了在代表局部天体分布的质量较小和较年轻端的星系中，WLyα和Lyα逃逸分数（fLyαesc）如何更高（WLyα <$20 μ m和fLyαesc <$10%）。这与各种性质有关，例如Lyα发射星系具有较低的金属丰度（中值为12 + log（O/H）~ 8.1）和尘埃变红。然而，星系外流/星系风的存在对于使Lyα线脱离与原子气体的共振也是至关重要的，并且只有在风速超过~ 50 km s−1的星系中才能发现高的WLyα。经验证据，然后组装成一个连贯的图片，和恒星形成驱动的反馈的要求进行了讨论的背景下，星际介质加速和/或受到流体动力学不稳定性，减少散射的Lyα的进化序列。结论性意见的形式是对未来发展的看法，以及可以通过观察回答的最紧迫的问题。
Abstract The Lyman alpha emission line (Lyα) of neutral hydrogen (Hi) is intrinsically the brightest emission feature in the spectrum of astrophysical nebulae, making it a very attractive observational feature with which to survey galaxies. Moreover as an ultraviolet resonance line, Lyα possesses several unique characteristics that make it useful to study the properties of the interstellar medium and ionising stellar population at all cosmic epochs. In this review, I present a summary of Lyα observations of galaxies in the nearby universe. By ultraviolet continuum selection, at the magnitudes reachable with current facilities, only ≈ 5% of the local galaxy population shows a Lyα equivalent width (WLyα) that exceeds 20 Å. This fraction increases dramatically at higher redshifts, but only in the local universe can we study galaxies in detail and assemble unprecedented multi-wavelength datasets. I discuss many local Lyα observations, showing that when galaxies show net Lyα emission, they ubiquitously also produce large-scale halos of scattered Lyα, that dominate the integrated luminosity. Concerning global measurements, we discuss how WLyα and the Lyα escape fraction (fLyαesc) are higher (WLyα ≳ 20 Å and fLyαesc ≳ 10%) in galaxies that represent the less massive and younger end of the distribution for local objects. This is connected with various properties, such that Lyα-emitting galaxies have lower metal abundances (median value of 12 + log(O/H) ~ 8.1) and dust reddening. However, the presence of galactic outflows/winds is also vital to Doppler shift the Lyα line out of resonance with the atomic gas, and high WLyα is found only among galaxies with winds faster than ~ 50 km s−1. The empirical evidence is then assembled into a coherent picture, and the requirement for star-formation-driven feedback is discussed in the context of an evolutionary sequence where the interstellar medium is accelerated and/or subject to hydrodynamical instabilities, which reduce the scattering of Lyα. Concluding remarks take the form of perspectives upon future developments, and the most pressing questions that can be answered by observation.