银河系的受激氢面纱
The Galaxy's Veil of Excited Hydrogen
摘要：
我们银河系中的许多重子可能位于众所周知的盘和核球成分之外。尽管有大量的证据表明星系晕中存在一些气体，包括类星体光谱中的吸收线系统、我们星系晕中的高速中性氢云、附近星暴星系中源自星系风的电离氢线，以及围绕大质量星系的X射线日冕，解释任何星系晕中的气体在观测上都是具有挑战性的，主要是因为它在膨胀的晕中的密度很低。最灵敏的测量来自于探测遥远物体光谱中的介入气体的吸收，如类星体或遥远的晕星，但这些通常仅限于足够明亮的物体的几条视线。对数以百万计的天体进行大规模的光谱测量为解决这个问题提供了另一种方法。在这里，我们提出了第一个证据，广泛分布的，中性的，兴奋的氢成分的银河系的光环。在数十万个星系光谱的组合光谱中，H $α$的静止波长附近的通量有轻微的吸收，吸收率为（0.779 $\pm$ 0.006）%，在高纬度视线中普遍存在。这一观测提供了一个途径来跟踪，空间和运动学，在我们的银河系晕的大部分气体。
英文摘要：
Many of the baryons in our Galaxy probably lie outside the well known disk and bulge components. Despite a wealth of evidence for the presence of some gas in galactic halos, including absorption line systems in the spectra of quasars, high velocity neutral hydrogen clouds in our Galaxy halo, line emitting ionised hydrogen originating from galactic winds in nearby starburst galaxies, and the X-ray coronas surrounding the most massive galaxies, accounting for the gas in the halo of any galaxy has been observationally challenging primarily because of its low density in the expansive halo. The most sensitive measurements come from detecting absorption by the intervening gas in the spectra of distant objects such as quasars or distant halo stars, but these have typically been limited to a few lines of sight to sufficiently bright objects. Massive spectroscopic surveys of millions of objects provide an alternative approach to the problem. Here, we present the first evidence for a widely distributed, neutral, excited hydrogen component of the Galaxy's halo. It is observed as the slight, (0.779 $\pm$ 0.006)\%, absorption of flux near the rest wavelength of H$α$ in the combined spectra of hundreds of thousands of galaxy spectra and is ubiquitous in high latitude lines of sight. This observation provides an avenue to tracing, both spatially and kinematically, the majority of the gas in the halo of our Galaxy.
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