渗透银河系CGM的亚太阳Fe/O、logT~7.5气体成分
A Sub-solar Fe/O, logT~7.5 Gas Component Permeating the Milky Way's CGM
AI总结：
本研究利用叠加的Chandra光谱和PHASE代码建模，发现银河系CGM中存在温度均匀但柱密度不均的hot气体成分，其非太阳丰度比表明该超位力气体相起源于星系反馈。
摘要：
我们的研究重点是表征银河系（MW）环星系介质（CGM）内的高电离气体，这些气体在2-25 Å的X射线波段产生离子跃迁。利用叠加的Chandra/ACISS MEG和LETG朝向类星体（QSO）视线方向的观测光谱，我们采用自洽的混合电离代码PHASE对数据进行建模。叠加光谱最优地由三个不同的气体相成分描述：warm（logT ~ 5.5）、warmhot（logT ~ 6）和hot（logT ~ 7.5）成分。这些发现证实了MW的CGM中存在hot成分，表明其与warm和warmhot气体相共存。我们发现该hot成分在温度上是均匀的，但在柱密度上是不均匀的。为了与文献中报告的银河系晕的色散测量（DM）一致，hot成分中的气体需要相对于太阳的过丰度。对于hot相，我们估计的DM = 55.1^{+29.9}_{-23.7} pc cm^{-3}。我们得出结论，该相要么在氧、硅和硫中富集，要么其金属丰度超过太阳值的6倍，或者是两者的结合。我们未检测到Fe L壳层吸收线，这意味着O/Fe ≥ 4。在银河系晕的超位力气体成分中发现的非太阳丰度比表明，该相起源于星系反馈。
英文摘要：
Our study focuses on characterizing the highly ionized gas within the Milky Way's (MW) Circumgalactic Medium (CGM) that gives rise to ionic transitions in the X-ray band 2 - 25 Å. Utilizing stacked \Chandra/\ACISS\ \MEG\ and \LETG\ spectra toward QSO sightlines, we employ the self-consistent hybrid ionization code PHASE to model our data. The stacked spectra are optimally described by three distinct gas phase components: a \warm\ (\logT\ $\sim$ 5.5), \warmhot\ (\logT\ $\sim 6$), and \hot\ (\logT\ $\sim$ 7.5) components. These findings confirm the presence of the \hot\ component in the MW's CGM indicating its coexistence with a \warm\ and a \warmhot\ gas phases. We find this \hot\ component to be homogeneous in temperature but inhomogeneous in column density. The gas in the \hot\ component requires over-abundances relative to solar to be consistent with the Dispersion Measure (DM) from the Galactic halo reported in the literature. {For the hot phase we estimated a DM = $55.1^{+29.9}_{-23.7}$ pc cm$^{-3}$}. We conclude that this phase is either enriched in Oxygen, Silicon, and Sulfur, or has metallicity {over 6} times solar value, or a combination of both. We do not detect Fe L-shell absorption lines, implying O/Fe $\geq$ 4. The non-solar abundance ratios found in the super-virial gas component in the Galactic halo suggest that this phase arises from Galactic feedback.
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