The Galactic TeV ${\gamma}$ -ray source ${\mathrm{HESS\,J}1804{-}216}$ is currently an unidentified source. In an attempt to unveil its origin, we present here the most detailed study of interstellar gas using data from the Mopra Southern Galactic Plane CO Survey, 7- and 12-mm wavelength Mopra surveys and Southern Galactic Plane Survey of HI. Several components of atomic and molecular gas are found to overlap ${\mathrm{HESS\,J}1804{-}216}$ at various velocities along the line of sight. The CS(1-0) emission clumps confirm the presence of dense gas. Both correlation and anti-correlation between the gas and TeV ${\gamma}$ -ray emission have been identified in various gas tracers, enabling several origin scenarios for the TeV ${\gamma}$ -ray emission from ${\mathrm{HESS\,J}1804{-}216}$ . For a hadronic scenario, ${\mathrm{SNR\,G}8.7{-}0.1}$ and the progenitor supernova remnant (SNR) of ${\mathrm{PSR\,J}1803{-}2137}$ require cosmic ray (CR) enhancement factors of ${\mathord{\sim} 50}$ times the solar neighbour CR flux value to produce the TeV ${\gamma}$ -ray emission. Assuming an isotropic diffusion model, CRs from both these SNRs require a slow diffusion coefficient, as found for other TeV SNRs associated with adjacent ISM gas. The morphology of gas located at 3.8 kpc (the dispersion measure distance to ${\mathrm{PSR\,J}1803{-}2137}$ ) tends to anti-correlate with features of the TeV emission from ${\mathrm{HESS\,J}1804{-}216}$ , making the leptonic scenario possible. Both pure hadronic and pure leptonic scenarios thus remain plausible.

中文翻译：

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对 HESS J1804-216 的星际气体的弧分尺度研究：仍然是一个未知的 TeV γ 射线源

银河TeV ${\伽马}$ -射线源 ${\mathrm{HESS\,J}1804{-}216}$ 目前是未知来源。为了揭示它的起源，我们在这里展示了最详细的星际气体研究，使用来自 Mopra 南部银河平面 CO2 调查、7 毫米和 12 毫米波长的 Mopra 调查和 HI 的南部银河平面调查的数据。原子和分子气体的几个成分被发现重叠 ${\mathrm{HESS\,J}1804{-}216}$ 以不同的速度沿着视线。CS(1-0) 发射团块证实了稠密气体的存在。气体和TeV之间的相关性和反相关性 ${\伽马}$ 已经在各种气体示踪剂中发现了射线发射，从而为 TeV 提供了几种起源情景 ${\伽马}$ - 射线发射 ${\mathrm{HESS\,J}1804{-}216}$ . 对于强子场景， ${\mathrm{SNR\,G}8.7{-}0.1}$ 和前身超新星遗迹（SNR） ${\mathrm{PSR\,J}1803{-}2137}$ 需要宇宙射线 (CR) 增强因子 ${\mathord{\sim} 50}$ 乘以太阳邻居 CR 通量值以产生 TeV ${\伽马}$ - 射线发射。假设采用各向同性扩散模型，来自这两个 SNR 的 CR 需要慢扩散系数，正如与相邻 ISM 气体相关的其他 TeV SNR 所发现的那样。位于 3.8 kpc 处的气体形态（分散测量距离到 ${\mathrm{PSR\,J}1803{-}2137}$ ) 倾向于与来自 TeV 发射的特征反相关 ${\mathrm{HESS\,J}1804{-}216}$ ，使轻子场景成为可能。因此，纯强子和纯轻子场景仍然是合理的。