The Nature of Ionized Gas in the Milky Way Galactic Fountain
The Nature of Ionized Gas in the Milky Way Galactic Fountain
复制标题
DOI：
10.3847/1538-4357/ab54cf
复制
发表时间：
2019-04
期刊：
影响因子：
--
通讯作者：
J. Werk;K. Rubin;H. Bish;J. Prochaska;Y. Zheng;J. O’Meara;D. Lenz;C. Hummels;A. Deason
中科院分区：
文献类型：
--
作者：
J. Werk;K. Rubin;H. Bish;J. Prochaska;Y. Zheng;J. O’Meara;D. Lenz;C. Hummels;A. Deason
我们解决的空间尺度，电离结构，质量和金属含量的气体在银河系盘晕界面检测到的吸收在前景的七个紧密间隔，高纬度晕蓝水平分支恒星高度z = 3-14千秒差距。我们检测跟踪多个电离状态的跃迁（例如，Ca ii，Fe ii，Si iv，C iv），柱密度随距盘的高度保持恒定，表明气体最有可能位于z < 3.4 kpc内。中间电离态气体跟踪C IV和Si IV是强烈相关的，在整个范围内的横向分离探测我们的视线，表明大，相干结构大于1千秒差距的大小。低电离状态的材料跟踪钙二和铁二不表现出相关性与NH i或横向分离，这意味着小于10 pc的尺度上的云或块状。我们发现，观测到的比值log（NSi iv/NC iv），中值为-0.69 ± 0.04，在光电离或碰撞电离的假设下，对电离气体的总碳含量敏感。光致电离气体的唯一自洽解决方案要求Si以相对于太阳Si/C比的0.35 dex耗尽到尘埃上，类似于DLAs和银河系星际介质中的Si耗尽水平。在盘-晕界面上，温暖的电离气体的面积质量下降率的允许值范围是0.0003 < dMgas/dtdA [M kpc−2 yr−1] <0.006。我们的数据支持一种物理场景，即银河系在其盘-晕界面处受到复杂的多相过程的馈送，这些过程涉及千秒差距尺度的电离包层或包含秒差距尺度的冷团块的流。
We address the spatial scale, ionization structure, mass, and metal content of gas at the Milky Way disk–halo interface detected as absorption in the foreground of seven closely spaced, high-latitude halo blue horizontal branch stars with heights z = 3–14 kpc. We detect transitions that trace multiple ionization states (e.g., Ca ii, Fe ii, Si iv, C iv) with column densities that remain constant with height from the disk, indicating that the gas most likely lies within z < 3.4 kpc. The intermediate ionization state gas traced by C iv and Si iv is strongly correlated over the full range of transverse separations probed by our sight lines, indicating large, coherent structures greater than 1 kpc in size. The low ionization state material traced by Ca ii and Fe ii does not exhibit a correlation with either NH i or transverse separation, implying cloudlets or clumpiness on scales less than 10 pc. We find that the observed ratio log(NSi iv/NC iv), with a median value of −0.69 ± 0.04, is sensitive to the total carbon content of the ionized gas under the assumption of either photoionization or collisional ionization. The only self-consistent solution for photoionized gas requires that Si be depleted onto dust by 0.35 dex relative to the solar Si/C ratio, similar to the level of Si depletion in DLAs and in the Milky Way interstellar medium. The allowed range of values for the areal mass infall rate of warm, ionized gas at the disk−halo interface is 0.0003 < dMgas/dtdA [M⊙ kpc−2 yr−1] <0.006. Our data support a physical scenario in which the Milky Way is fed by complex, multiphase processes at its disk−halo interface that involve kiloparsec-scale ionized envelopes or streams containing parsec-scale, cool clumps.