论文标题
在扩展HII区域的湍流驾驶模式下
On the turbulence driving mode of expanding HII regions
论文作者
论文摘要
我们研究了从周围星际培养基（ISM）上的巨大恒星电离辐射的湍流驱动模式。我们运行了由平面平行电离沿撞击的湍流云的流体动力模拟。我们发现电离辐射形成了中性气体的支柱，让人联想到观测中看到的辐射。我们通过计算驱动参数$ b $来量化中性气体中的湍流模式，该驱动参数的特征是关系$σ_s^2 = \ ln（{1+b^2 \ Mathcal {M}^2}^2} $使用气体密度$ρ$及其平均$ρ_0$），而动荡的马赫数$ \ MATHCAL {M} $。以前的工作表明，$ b \ sim1/3 $表示螺线管（无差异）驾驶，$ b \ sim1 $表示抗压（无卷曲）驾驶，其中$ b \ sim1 $产生的恒星编队率最高为$ b \ sim1/3 $。在我们的研究中，$ b $的时间变化使我们可以推断电离辐射本质上是压缩湍流驱动器，其时间平均$ b \ sim 0.76 \ pm 0.08 $。我们还研究了预计会发生恒星形成的支柱的$ b $的价值，并发现该支柱的特征是螺线管和压缩湍流模式（$ b \ sim0.4 $）的自然混合物，后来又演变成更紧缩的湍流状态，带有$ b \ sim0.5 $ - $ 0.6 $ 0.6 $。对支柱区域的病毒参数分析支持了这一结论。这表明来自巨大恒星的电离辐射可能能够通过在支柱中产生主要压缩湍流气体来触发恒星形成。
We investigate the turbulence driving mode of ionizing radiation from massive stars on the surrounding interstellar medium (ISM). We run hydrodynamical simulations of a turbulent cloud impinged by a plane-parallel ionization front. We find that the ionizing radiation forms pillars of neutral gas reminiscent of those seen in observations. We quantify the driving mode of the turbulence in the neutral gas by calculating the driving parameter $b$, which is characterised by the relation $σ_s^2 = \ln({1+b^2\mathcal{M}^2})$ between the variance of the logarithmic density contrast $σ_s^2$ (where $s = \ln({ρ/ρ_0})$ with the gas density $ρ$ and its average $ρ_0$), and the turbulent Mach number $\mathcal{M}$. Previous works have shown that $b\sim1/3$ indicates solenoidal (divergence-free) driving and $b\sim1$ indicates compressive (curl-free) driving, with $b\sim1$ producing up to ten times higher star formation rates than $b\sim1/3$. The time variation of $b$ in our study allows us to infer that ionizing radiation is inherently a compressive turbulence driving source, with a time-averaged $b\sim 0.76 \pm 0.08$. We also investigate the value of $b$ of the pillars, where star formation is expected to occur, and find that the pillars are characterised by a natural mixture of both solenoidal and compressive turbulent modes ($b\sim0.4$) when they form, and later evolve into a more compressive turbulent state with $b\sim0.5$--$0.6$. A virial parameter analysis of the pillar regions supports this conclusion. This indicates that ionizing radiation from massive stars may be able to trigger star formation by producing predominately compressive turbulent gas in the pillars.
