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arXiv 2002.06434astro-ph.GA
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MW中的热气体运动学模型

The Warm Gas in the MW: A Kinematical Model

Zhijie Qu, Joel N. Bregman, Edmund Hodges-Kluck, Jiang-Tao Li, Ryan Lindley

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Accepted by ApJ
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摘要：

我们开发了一个银河系硅IV轴承气体的运动学模型，以确定其密度分布和运动学。该模型由从{ \it HST}/COS存档数据中提取的柱密度线形状样本约束，该样本包含186条活动星系核视线。我们发现Si IV离子密度分布由沿$z$方向（在中平面上方或下方）的扩展盘主导，即，$n(z)=n_0\exp(-(z/z_0)^{0.82})$，其中$z_0$是$6.3_{-1.5}^{+1.6}$ kpc（北半球）和$3.6_{-0.9}^{+1.0}$ kpc（南半球）的标度高度。圆盘在径向上的密度分布在$15-20$ kpc处显示出锐边，由$n(r_{\rm XY})=n_0\exp(-(r_{\rm XY}/r_0)^{3.36})$给出，其中$r_0 \approx 12.5\pm0.6$ kpc。$r_{\rm XY}$和$z$方向上密度分布的差异表明，\ion{Si}{4}追踪的暖气体主要与盘过程有关（例如，反馈或循环气体）而不是吸积。我们估计热气体的质量（在50千秒差距以内）是$\log (M(50 {\rm kpc})/M_\odot)\approx8.1$（假设是$Z\approx0.5Z_\odot$），$3σ$的上限是$\log (M(250 {\rm kpc})/M_\odot)\approx9.1$（不包括麦哲伦星系）。在运动学上，温暖的气体盘几乎与恒星盘在$v_{\rm rot}=215\pm3\rm~km~s^{-1}$处同向旋转，这比中平面旋转滞后大约$8\rm~km~s^{-1}~kpc^{-1}$（5 kpc以内）。同时，我们注意到，在北半球的温暖的气体与$69\pm 7\rm ~km~s^{-1}$的$v_{\rm acc}$在10 kpc的吸积（吸积率为$-0.60_{-0.13}^{+0.11}~M_\odot\rm~yr^{-1}$），而在南半球，没有可测量的吸积，上限为$0.4~M_\odot\rm~yr^{-1}$。

英文摘要：

We develop a kinematical model for the Milky Way Si IV-bearing gas to determine its density distribution and kinematics. This model is constrained by a column density line shape sample extracted from the {\it HST}/COS archival data, which contains 186 AGN sight lines. We find that the Si IV ion density distribution is dominated by an extended disk along the $z$-direction (above or below the midplane), i.e., $n(z)=n_0\exp(-(z/z_0)^{0.82})$, where $z_0$ is the scale height of $6.3_{-1.5}^{+1.6}$ kpc (northern hemisphere) and $3.6_{-0.9}^{+1.0}$ kpc (southern hemisphere). The density distribution of the disk in the radial direction shows a sharp edge at $15-20$ kpc given by, $n(r_{\rm XY})=n_0\exp(-(r_{\rm XY}/r_0)^{3.36})$, where $r_0 \approx 12.5\pm0.6$ kpc. The difference of density distributions over $r_{\rm XY}$ and $z$ directions indicates that the warm gas traced by \ion{Si}{4} is mainly associated with disk processes (e.g., feedback or cycling gas) rather than accretion. We estimate the mass of the warm gas (within 50 kpc) is $\log (M(50 {\rm kpc})/M_\odot)\approx8.1$ (assuming $Z\approx0.5Z_\odot$), and a $3σ$ upper limit of $\log (M(250 {\rm kpc})/M_\odot)\approx9.1$ (excluding the Magellanic system). Kinematically, the warm gas disk is nearly co-rotating with the stellar disk at $v_{\rm rot}=215\pm3\rm~km~s^{-1}$, which lags the midplane rotation by about $8\rm~km~s^{-1}~kpc^{-1}$ (within 5 kpc). Meanwhile, we note that the warm gas in the northern hemisphere has significant accretion with $v_{\rm acc}$ of $69\pm 7\rm ~km~s^{-1}$ at 10 kpc (an accretion rate of $-0.60_{-0.13}^{+0.11}~M_\odot\rm~yr^{-1}$), while in the southern hemisphere, there is no measurable accretion, with an upper limit of $0.4~M_\odot\rm~yr^{-1}$.

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