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arXiv 1409.4874astro-ph.GA
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漫长的路要走:来自大星系的外流如何通过热晕气体传播

Long way to go: how outflows from large galaxies propagate through the hot halo gas

Kartick Chandra Sarkar, Biman B. Nath, Prateek Sharma, Yuri Shchekinov

摘要:

利用流体动力学模拟,我们研究了银河系盘状星系由于超新星驱动的外流而导致的质量损失,特别注意扩展的热晕气体的影响。我们发现,总的质量损失在内部半径的比例大致线性与形成的恒星的总质量,并在维里半径的质量负载因子可以是几倍,因为席卷了热晕气体在内部半径的值。在内部区域($\sim $ 10 kpc)中流出材料的温度分布本质上是双峰的,峰值在$10^5$ K和$10^{6.5}$ K处,分别负责光学和X射线发射。温度为$\le 10^{5.5}$ K的冷/暖气体对10 kpc内流出速率的贡献为$\approx 0.3\hbox{--}0.5$。当重子分数为0.1,恒星暴周期为5000万年时,热质量负载因子$η_{3e5}$($T\le 3 \times 10^5$ K)与维里半径处的质量负载因子($η_{v}$)相关,为$η_{v} \approx 25\, η_{3e5}\, \left(\mbox{SFR}/{\rm M}_\odot{\rm yr}^{-1} \right)^{-0.15}$。我们还讨论了由短周期和长周期分开的多个爆发的影响。在维里半径处的流出速度接近于热晕中的声速,$\lesssim 200$ km s $^{-1}$。我们确定了两个“序列”的流出冷气体在小尺度:快速($\approx 500$公里~s $^{-1}$)序列,由未受冲击的自由风驱动;和一个缓慢的序列($\approx \pm 100$公里s $^{-1}$)在锥形界面的超级风和热晕。

英文摘要:

Using hydrodynamic simulations, we study the mass loss due to supernova-driven outflows from Milky Way type disk galaxies, paying particular attention to the effect of the extended hot halo gas. We find that the total mass loss at inner radii scales roughly linearly with total mass of stars formed, and that the mass loading factor at the virial radius can be several times its value at inner radii because of the swept up hot halo gas. The temperature distribution of the outflowing material in the inner region ($\sim $10 kpc) is bimodal in nature, peaking at $10^5$ K and $10^{6.5}$ K, responsible for optical and X-ray emission, respectively. The contribution of cold/warm gas with temperature $\le 10^{5.5}$ K to the outflow rate within 10 kpc is $\approx 0.3\hbox{--}0.5$. The warm mass loading factor, $η_{3e5}$ ($T\le 3 \times 10^5$ K) is related to the mass loading factor at the virial radius ($η_{v}$) as $η_{v} \approx 25\, η_{3e5}\, \left(\mbox{SFR}/{\rm M}_\odot{\rm yr}^{-1} \right)^{-0.15}$ for a baryon fraction of 0.1 and a starburst period of 50 Myr. We also discuss the effect of multiple bursts that are separated by both short and long periods. The outflow speed at the virial radius is close to the sound speed in the hot halo, $\lesssim 200$ km s$^{-1}$. We identify two `sequences' of outflowing cold gas at small scales: a fast ($\approx 500$ km~s$^{-1}$) sequence, driven by the unshocked free-wind; and a slow sequence ($\approx \pm 100$ km s$^{-1}$) at the conical interface of the superwind and the hot halo.

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