标题： 螺旋星系中的盘外气体的动力学模型 显示英文标题

标题： A Dynamical Model for the Extra-planar Gas in Spiral Galaxies

摘要： 近期的氢气（HI）观测显示，螺旋星系的盘面被延伸的气体晕所包围。 这种盘外气体到达远离盘面的大距离（数kpc），并表现出特殊的动力学特性（低旋转速度和内流）。 我们将盘外气体建模为从螺旋星系盘面向其晕区持续流动的物质。 我们的模型输出的是伪数据立方体，可以直接与HI观测数据进行比较。 我们已经将这些模型应用于两个已知拥有大量盘外气体的螺旋星系（NGC891和NGC2403）。 我们的模型能够准确再现盘外气体的垂直分布，对于超新星释放能量的小部分（<4%）作为能量输入时尤其如此。 然而，在两个重要方面它们未能成功：1）它们无法再现正确的旋转速度梯度；2）它们预测盘外气体总体上向外流出，这与观测结果相反。 我们表明，如果云团在离开盘面时被电离且在21厘米波段不可见，但在轨道上的某个点变得可见，那么上述困难都无法消除。 我们推测，这些失败可能表明需要从星系际介质（IGM）吸积物质，以提供所需的低角动量和内流。 显示英文摘要

摘要： Recent HI observations reveal that the discs of spiral galaxies are surrounded by extended gaseous haloes. This extra-planar gas reaches large distances (several kpc) from the disc and shows peculiar kinematics (low rotation and inflow). We have modelled the extra-planar gas as a continuous flow of material from the disc of a spiral galaxy into its halo region. The output of our models are pseudo-data cubes that can be directly compared to the HI data. We have applied these models to two spiral galaxies (NGC891 and NGC2403) known to have a substantial amount of extra-planar gas. Our models are able to reproduce accurately the vertical distribution of extra-planar gas for an energy input corresponding to a small fraction (<4%) of the energy released by supernovae. However they fail in two important aspects: 1) they do not reproduce the right gradient in rotation velocity; 2) they predict a general outflow of the extra-planar gas, contrary to what is observed. We show that neither of these difficulties can be removed if clouds are ionized and invisible at 21cm as they leave the disc but become visible at some point on their orbits. We speculate that these failures indicate the need for accreted material from the IGM that could provide the low angular momentum and inflow required.