论文标题
GMC表面密度的质量大小关系和恒定
The Mass-Size Relation and the Constancy of GMC Surface Densities in the Milky Way
论文作者
论文摘要
我们使用来自同一CO调查的两个现有分子云目录，并使用局部尘埃灭绝调查得出的两个目录来研究银河系中GMC质量大小关系的性质。我们发现这四个调查由$ m_ {gmc} \ sim r^2 $很好地描述，这意味着针对云的云而表示恒定平均表面密度，$σ_{gmc} $。但是，缩放系数和散射在CO和灭绝关系之间存在显着差异。我们发现，在CO关系中看到的附加散射是由于$σ_{gmc} $的系统变化带有银河半径，而局部灭绝数据中无法观察到。我们将$σ_{gmc} $的径向变化分解为两个组件，是带有银河半径的线性负梯度，与分子环和线性梯度上的超级峰一致。我们表明，前者可能是由于X $ _ {CO} $对金属性的径向依赖性所致，而后者可能是由于单个GMC的表面密度增加而导致的，并且在$σ_{GMC} $的测量中，由于分子环中的云混合而导致的$σ_{GMC} $。我们将CO和灭绝数据之间的缩放系数差异归因于x $ _ {CO} $的低估。我们使用灭绝测量值重新校准了附近GMC的CO观察，以发现本地X $ _ {CO} $ = $ = $ 3.6 $ \ pm $ 0.3 $ 0.3 $ \ times $ 10 $^{20} $ CM $ $^{ - 2} $（k-kmm/ss）$^{ - 1} $^{ - 1} $。我们得出的结论是，在分子环之外，可以将银河系的GMC种群描述为相对较好的精度，即常数$σ_{gmc} $ 35 m $ _ $ _ \ odot $ pc $^{ - 2} $。
We use two existing molecular cloud catalogs derived from the same CO survey and two catalogs derived from local dust extinction surveys to investigate the nature of the GMC mass-size relation in the Galaxy. We find that the four surveys are well described by $M_{GMC} \sim R^2$ implying a constant mean surface density, $Σ_{GMC}$, for the cataloged clouds. However, the scaling coefficients and scatter differ significantly between the CO and extinction derived relations. We find that the additional scatter seen in the CO relations is due to a systematic variation in $Σ_{GMC}$ with Galactic radius that is unobservable in the local extinction data. We decompose this radial variation of $Σ_{GMC}$ into two components, a linear negative gradient with Galactic radius and a broad peak coincident with the molecular ring and superposed on the linear gradient. We show that the former may be due to a radial dependence of X$_{CO}$ on metallicity while the latter likely results from a combination of increased surface densities of individual GMCs and a systematic upward bias in the measurements of $Σ_{GMC}$ due to cloud blending in the molecular ring. We attribute the difference in scaling coefficients between the CO and extinction data to an underestimate of X$_{CO}$. We recalibrate the CO observations of nearby GMCs using extinction measurements to find that locally X$_{CO}$ $=$ 3.6$\pm$0.3 $\times$ 10$^{20}$ cm$^{-2}$ (K-km/s)$^{-1}$. We conclude that outside the molecular ring the GMC population of the Galaxy can be described to relatively good precision by a constant $Σ_{GMC}$ of 35 M$_\odot$ pc$^{-2}$.
