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首页> 外文期刊>PASJ: Publications of the Astronomical Society of Japan >Three-dimensional distribution of the ISM in the Milky Way Galaxy. IV. 3D molecular fraction and Galactic-scale H-I-to-H-2 transition
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Three-dimensional distribution of the ISM in the Milky Way Galaxy. IV. 3D molecular fraction and Galactic-scale H-I-to-H-2 transition

机译：银河系中ISM的三维分布。 IV。 3D分子分数和银级H-1至H-2过渡

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摘要

Three-dimensional (3D) distribution of the volume-density molecular fraction, defined by f(mol)(rho) =rho H-2/(rho H-I +rho H-2), is studied in the Milky Way Galaxy. The molecular front appears at galacto-centric distance of R similar to 8 kpc, where the galactic-scale phase transition from atomic to molecular hydrogen occurs with f(mol)(rho) dropping from similar to 0.8 to 0.2 within a radial interval as narrow as similar to 0.5 kpc. The f(mol)(rho) front is much sharper than that of the surface density molecular fraction. The f(mol)(rho) front also appears in the direction vertical to the galactic plane with a full width of the high-f(mol)(rho) disk to be similar to 100 pc. The radial and vertical f(mol)(rho) profiles, particularly the front behavior, are fitted by theoretical curves calculated using the observed density profile and assumed radiation field and metallicity with exponential gradients. The molecular fraction was found to be enhanced along spiral arms at radii R similar to 6 to 10 kpc, such as the Perseus arm. This implies that the molecular clouds are produced from HI in the arms and are dissociated in the interarm regions in the transition region around the molecular front. We also show that there is a threshold value of mean HI density, over which HI is transformed into molecular gas.
机译：在银河系中研究了由f（mol）（rho）= rho H-2 /（rho H-1 + rho H-2）定义的体积密度分子分数的三维（3D）分布。分子前沿出现在R的半乳糖中心距离处，类似于8 kpc，其中发生了从原子氢到分子氢的银河系尺度相变，其中f（mol）（rho）在类似径向范围内的径向范围内从相似的0.8下降到0.2到0.2。类似于0.5 kpc。 f（mol）（rho）峰比表面密度分子分数的峰锐得多。 f（mol）（rho）正面也出现在垂直于银河平面的方向上，高f（mol）（rho）盘的整个宽度类似于100 pc。径向和垂直f（mol）（rho）轮廓，特别是前部行为，通过理论曲线拟合，该理论曲线使用观察到的密度曲线以及假定的辐射场和金属性以及指数梯度来计算。发现该分子部分沿着螺旋臂在半径R处得到增强，该半径类似于6至10 kpc，例如英仙座臂。这意味着分子云是由臂中的HI产生的，并在围绕分子前沿的过渡区域中的臂间区域解离。我们还表明，存在一个平均HI密度阈值，在该阈值上HI转化为分子气体。

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