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arXiv 2201.09995astro-ph.GAastro-ph.SR
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分子云中的远极UV辐射反馈及其对星团质量和大小的影响

Far and extreme UV radiation feedback in molecular clouds and its influence on the mass and size of star clusters

Hajime Fukushima, Hidenobu Yajima

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20 pages, 17 figures, accepted for publication in MNRAS
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摘要：

利用远紫外（FUV; $6 ~{\rm eV} \leqq h ν\leqq 13.6 ~{\rm eV}$）和极紫外（EUV; $hν\geqq 13.6~{\rm eV}$）辐射反馈进行三维辐射流体力学模拟，研究了分子云中星团的形成过程。我们发现，FUV反馈显着抑制恒星形成的弥漫云与初始表面密度的$Σ_{\rm cl} \lesssim \rm 50~M_{\odot} \; pc^{-2}$。在含$Σ_{\rm cl} \sim \rm 100-200~M_{\odot} \; pc^{-2}$的星云中，EUV反馈起主要作用，降低的恒星形成效率小于$0.3$。我们发现，来自PDR或H{ \sc ii}区域的热压力破坏了云，使星团的大小更大。因此，质量为$M_{\rm cl} \lesssim 10^{5}~\rm M_{\odot}$、表面密度为$Σ_{\rm cl} \lesssim 200~\rm M_{\odot}\; pc^{-2}$的云仍然是恒星密度为$\sim 100~\rm M_{\odot}\; pc^{-3}$的星团，与银河系中观测到的疏散星团非常匹配。如果分子云是大质量的（$M_{\rm cl} \gtrsim 10^{5}~\rm M_{\odot}$）和致密的（$Σ\gtrsim 400~\rm M_{\odot}\; pc^{-2}$），则辐射反馈不起作用，它们形成大质量的致密星团，其恒星密度为$\sim 10^{4}~\rm M_{\odot}\; pc^{-3}$，类似于观测到的球状星团或年轻的大质量星团。因此，我们认为辐射反馈和分子云的初始条件是导致观测到的星团变化的关键因素。

英文摘要：

We study the formation of star clusters in molecular clouds by performing three-dimensional radiation hydrodynamics simulations with far ultraviolet (FUV; $6 ~{\rm eV} \leqq h ν\leqq 13.6 ~{\rm eV}$) and extreme ultraviolet (EUV; $hν\geqq 13.6~{\rm eV}$) radiative feedback. We find that the FUV feedback significantly suppresses the star formation in diffuse clouds with the initial surface densities of $Σ_{\rm cl} \lesssim \rm 50~M_{\odot} \; pc^{-2}$. In the cases of clouds with $Σ_{\rm cl} \sim \rm 100-200~M_{\odot} \; pc^{-2}$, the EUV feedback plays a main role and decrease the star formation efficiencies less than $0.3$. We show that thermal pressure from PDRs or H{\sc ii} regions disrupts the clouds and makes the size of the star clusters larger. Consequently, the clouds with the mass $M_{\rm cl} \lesssim 10^{5}~\rm M_{\odot}$ and the surface density $Σ_{\rm cl} \lesssim 200~\rm M_{\odot}\; pc^{-2}$ remain the star clusters with the stellar densities of $\sim 100~\rm M_{\odot}\; pc^{-3}$ that nicely match the observed open clusters in the Milky Way. If the molecular clouds are massive ($M_{\rm cl} \gtrsim 10^{5}~\rm M_{\odot}$) and compact ($Σ\gtrsim 400~\rm M_{\odot}\; pc^{-2}$), the radiative feedback is not effective and they form massive dense cluster with the stellar densities of $\sim 10^{4}~\rm M_{\odot}\; pc^{-3}$ like observed globular clusters or young massive star clusters. Thus, we suggest that the radiative feedback and the initial conditions of molecular clouds are key factors inducing the variety of the observed star clusters.

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