费米气泡中的高速中性气体：新的运动学限制与空间结构
High Velocity Neutral Gas in the Fermi Bubbles: New Kinematic Limits and Spatial Structure
AI总结：
本研究基于绿岸望远镜的HI数据，探测到费米气泡中的数百个中性云，明确了其速度分布、加速特征及空间截断，揭示外流曾存在方位不对称性，为银河系核风研究提供了关键观测约束。
AI中文摘要：
我们利用绿岸望远镜开展的新巡天项目获取的中性氢（HI）数据，在覆盖银心（GC）周围约500平方度的天区范围内，探测到了数百个被银河系核风裹挟的中性云。星系风在宇宙中普遍存在，本次9.1角分（对应银心处22秒差距）角分辨率的数据，为研究任何星系中中性核风的垂直剖面提供了最详细的分析。我们选取了228个具有最大|V_LSR|值的费米气泡云，对这些外流气体的分布和运动学特征进行分析。这些云的V_LSR范围为-335 km/s ≤ V_LSR ≤ +438 km/s，是迄今为止报道的与银河系盘相关的中性HI的最大正LSR速度。最高速度出现在离银心最远的位置，表明这些云从核附近的低速度被加速到径向距离≲4千秒差距处时，速度至少达到500 km/s。云在加速过程中呈现出被扰动的状态：它们的线亮度和中性氢柱密度（N_HI）随与银心的距离增加而稳步降低，且云群变得更加均匀。在距银道面垂直距离约2千秒差距处，中性云存在一个突然的截断。我们利用填充费米气泡（FB）体积的外流云群运动学模型，识别气体中的结构。最高速度、最高银纬云的运动学特征，暗示该外流在过去存在方位不对称性。
英文摘要：
We have detected hundreds of neutral clouds entrained in the Milky Way's nuclear wind using HI data from new surveys made with the Green Bank Telescope that cover about 500 sq-degrees around the Galactic center (GC). Galactic winds are common throughout the Universe, and these data at 9.1' angular resolution (22 pc at the GC) provide the most detailed analysis of the vertical profile of a neutral nuclear wind in any galaxy. A set of 228 of these Fermi Bubble clouds with the largest values of |VLSR| has been analyzed to examine the distribution and kinematics of the outflowing gas. The clouds span -335 km/s $\leq$ VLSR $\leq$ +438 km/s, the largest positive LSR velocities ever reported for neutral HI associated with the Milky Way disk. The highest velocities are found furthest from the GC, suggesting that clouds are accelerated from a low velocity near the nucleus to at least 500 km/s at a radial distance of $\lesssim 4$ kpc. Clouds appear disrupted as they are accelerated: their line brightness and NHI decreases steadily with distance from the GC, and the population becomes more uniform. There is an abrupt cutoff in the neutral clouds at a vertical distance of $\approx2$ kpc from the Galactic plane. Kinematic models of an outflowing cloud population that fills the FB volume are used to identify structure in the gas. The kinematics of the highest velocity, highest latitude clouds imply a past azimuthal asymmetry in the outflow.
