Mapping Outflowing Gas in the Fermi Bubbles: A UV Absorption Survey of the Galactic Nuclear Wind
Mapping Outflowing Gas in the Fermi Bubbles: A UV Absorption Survey of the Galactic Nuclear Wind
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DOI：
10.3847/1538-4357/ab9ff8
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发表时间：
2020-08-01
影响因子：
4.9
通讯作者：
Karim, Tanveer
中科院分区：
文献类型：
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作者：
Ashley, Trisha;Fox, Andrew J.;Karim, Tanveer
利用哈勃太空望远镜上的宇宙起源光谱仪（Cosmic Origins Spectrograph）对5个背景类星体的紫外（UV）光谱，我们分析了银河系中心巨大的伽玛射线发射叶费米气泡（Fermi Bubbles）的低纬度（垂线b垂线= 20度-30度）区域。我们将这些数据与之前的UV和原子氢（Hi）数据集结合起来，建立了一个关于费米气泡中冷流出云的运动学和金属柱密度的综合图像。我们发现，每条视线中紫外线吸收成分的数量随着纬度的增加而减少，这表明外流云随着纬度的增加而减少。费米气泡云被加速到大约7度，而当我们模拟UV费米气泡云的预估流速时，我们发现它们是平坦的，甚至随着距离银河系中心的距离而加速。这种趋势在北半球和南半球都存在，表明核流出加速了整个费米气泡中的云，或者有一个加速阶段，然后是滑行阶段。最后，我们注意到在纬度超过类似于30度的地方存在几个蓝移高速云，其速度不能用伽马射线定义的费米气泡内部的气体云来解释。这些速度异常的云很可能在费米气泡的前面，可能是过去核流出的残余物。总的来说，这些观测形成了一组有价值的经验数据，用于研究来自恒星形成星系的核风中的冷气体的特性。
Using new ultraviolet (UV) spectra of five background quasars from the Cosmic Origins Spectrograph on the Hubble Space Telescope, we analyze the low-latitude (vertical bar b vertical bar = 20 degrees-30 degrees) regions of the Fermi Bubbles, the giant gamma-ray-emitting lobes at the Galactic Center. We combine these data with previous UV and atomic hydrogen (Hi) data sets to build a comprehensive picture of the kinematics and metal column densities of the cool outflowing clouds entrained in the Fermi Bubbles. We find that the number of UV absorption components per sight line decreases as a function of increasing latitude, suggesting that the outflowing clouds become less common with increasing latitude. The Fermi Bubble Hiclouds are accelerated up to b similar to 7 degrees, whereas when we model the UV Fermi Bubbles clouds' deprojected flow velocities, we find that they are flat or even accelerating with distance from the Galactic center. This trend, which holds in both the northern and southern hemispheres, indicates that the nuclear outflow accelerates clouds throughout the Fermi Bubbles or has an acceleration phase followed by a coasting phase. Finally, we note the existence of several blueshifted high-velocity clouds at latitudes exceeding similar to 30 degrees, whose velocities cannot be explained by gas clouds confined to the inside of the gamma-ray-defined Fermi Bubbles. These anomalous-velocity clouds are likely in front of the Fermi Bubbles and could be remnants from past nuclear outflows. Overall, these observations form a valuable set of empirical data on the properties of cool gas in nuclear winds from star-forming galaxies.