arXiv 1608.054152016-08astro-ph.GA

Milky Way巨分子云中动态恒星形成率的观测证据

Observational Evidence of Dynamic Star Formation Rate in Milky Way Giant Molecular Clouds

Eve J. Lee, Marc-Antoine Miville-Deschenes, Norman Murray

备注：: accepted to ApJ; we added a discussion of multi-freefall models of star formation
DOI：: 10.3847/1538-4357/833/2/229

摘要：

已知星系尺度上的恒星形成是一个缓慢的过程，但在较小尺度上是否缓慢还不确定。我们交叉关联5469巨分子云（GMCs）从一个新的全天空目录与256恒星形成复合体（SFCs），建立一个样本的191 SFC-GMC复合体--收集多个云每个匹配到191 SFCs。这些云所包含的恒星的总质量是从WMAP的自由-自由通量推断出来的。我们测量了GMC质量、维里参数、恒星形成效率$ε$和单位自由落体时间的恒星形成率$ε_{\rm ff}$。$ε$和$ε_{\rm ff}$的范围都超过3- 4个数量级。我们发现，68.3%的云落在$σ_{\logε}=0.79\pm0.22\,{\rm dex}$和$σ_{\logε_{\rm ff}}=0.91\pm0.22\,{\rm dex}$的中位数。与这些观察到的散射相比，具有依赖于宿主GMC性质的与时间无关的$ε_{\rm ff}$的简单模型预测$σ_{\logε_{\rm ff}}=$为$σ_{\logε_{\rm ff}}=$ 0.12-0.24。考虑到时间变量$ε_{\rm ff}$，我们可以恢复恒星形成速率的大色散。这有力地表明，银河系中的恒星形成是一个GMC尺度上的动态过程。我们还表明，银河系的表面恒星形成率分布与分子气体表面密度分布相关。

英文摘要：

Star formation on galactic scales is known to be a slow process, but whether it is slow on smaller scales is uncertain. We cross-correlate 5469 giant molecular clouds (GMCs) from a new all-sky catalog with 256 star forming complexes (SFCs) to build a sample of 191 SFC-GMC complexes---collections of multiple clouds each matched to 191 SFCs. The total mass in stars harbored by these clouds is inferred from WMAP free-free fluxes. We measure the GMC mass, the virial parameter, the star formation efficiency $ε$ and the star formation rate per free-fall time $ε_{\rm ff}$. Both $ε$ and $ε_{\rm ff}$ range over 3--4 orders of magnitude. We find that 68.3% of the clouds fall within $σ_{\logε}=0.79\pm0.22\,{\rm dex}$ and $σ_{\logε_{\rm ff}}=0.91\pm0.22\,{\rm dex}$ about the median. Compared to these observed scatters, a simple model with a time independent $ε_{\rm ff}$ that depends on the host GMC properties predicts $σ_{\logε_{\rm ff}}=$0.12-0.24. Allowing for a time-variable $ε_{\rm ff}$, we can recover the large dispersion in the rate of star formation. This strongly suggests that star formation in the Milky Way is a dynamic process on GMC scales. We also show that the surface star formation rate profile of the Milky Way correlates well with the molecular gas surface density profile.

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