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arXiv 1806.04832astro-ph.GA
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朱雀X射线观测对Milky Way热气晕空间分布的约束

Spatial distribution of the Milky Way hot gaseous halo constrained by Suzaku X-ray observations

Shinya Nakashima, Yoshiyuki Inoue, Noriko Yamasaki, Yoshiaki Sofue, Jun Kataoka, Kazuhiro Sakai

摘要:

与银河系有关的热气晕的形成机制仍在争论之中。我们使用107线的朱雀X射线观测在$75^{\circ}<l<285^{\circ}$和$|b|>15^{\circ}$的总曝光量为6.4毫秒的气体晕的新的观测约束。气体晕光谱表示的碰撞电离平衡的单温度等离子体模型。观测场的中值温度为0.26 keV($3.0\times10^6$ K),具有$\sim30$ %的典型波动。发射量的变化是一个数量级,与银河系的纬度略有相关。尽管数据的分散性很大,但排放测量分布大致上是由盘状密度分布再现的,其标度长度为$\sim7$ kpc,标度高度为$\sim2$ kpc,总质量为$\sim5\times10^7$ $M_{\odot}$。此外,我们发现,一个球形的热气体与$β$模型的轮廓几乎没有贡献的观察到的X射线,但它的总质量可能达到$\gtrsim10^9$ $M_{\odot}$。结合从其他观测得到的扩展气体晕的间接证据,热气体晕可能由致密的盘状成分和稀薄的球形成分组成; X射线发射主要来自前者,但质量由后者主导。盘状成分可能源于银河系盘中的恒星反馈,由于低尺度高度和发射测量的大散射。$\sim0.25$的中值[O/Fe]表明了核心坍缩超新星的贡献,支持恒星反馈起源。

英文摘要:

The formation mechanism of the hot gaseous halo associated with the Milky Way Galaxy is still under debate. We report new observational constraints on the gaseous halo using 107 lines-of-sight of the Suzaku X-ray observations at $75^{\circ}<l<285^{\circ}$ and $|b|>15^{\circ}$ with a total exposure of 6.4 Ms. The gaseous halo spectra are represented by a single-temperature plasma model in collisional ionization equilibrium. The median temperature of the observed fields is 0.26 keV ($3.0\times10^6$ K) with a typical fluctuation of $\sim30$%. The emission measure varies by an order of magnitude and marginally correlates with the Galactic latitude. Despite the large scatter of the data, the emission measure distribution is roughly reproduced by a disk-like density distribution with a scale length of $\sim7$ kpc, a scale height of $\sim2$ kpc, and a total mass of $\sim5\times10^7$ $M_{\odot}$. In addition, we found that a spherical hot gas with the $β$-model profile hardly contributes to the observed X-rays but that its total mass might reach $\gtrsim10^9$ $M_{\odot}$. Combined with indirect evidence of an extended gaseous halo from other observations, the hot gaseous halo likely consists of a dense disk-like component and a rarefied spherical component; the X-ray emissions primarily come from the former but the mass is dominated by the latter. The disk-like component likely originates from stellar feedback in the Galactic disk due to the low scale height and the large scatter of the emission measures. The median [O/Fe] of $\sim0.25$ shows the contribution of the core-collapse supernovae and supports the stellar feedback origin.

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