Magnetic fields, outflows and feedback in spiral galaxies

螺旋星系被气态晕包围，这些气态晕显示出相当大的结构，并将星系盘内的星际介质(ISM，恒星之间的气体)连接到周围环境。越来越多的证据表明，这些晕是动态实体；也就是说，它们表明尘埃、气体(电离的、中性的和分子的)、宇宙射线和磁场从星系盘中喷出。目前尚不清楚的是，有多少星系和哪种类型的星系更有可能出现这样的光晕，有多少被排出的物质再次循环回到盘面，有多少物质离开银河系，丰富了星际介质(IGM，星系之间的低密度气体)。我们知道，这种外流(或“反馈”)在星系的形成中起着至关重要的作用，但这一活动的性质和细节尚不为人所知。证据表明，星系演化(包括我们所在的银河系)受到这种活动的强烈影响，但我们甚至不知道这种活动的主要驱动力。

Spiral galaxies are surrounded by gaseous halos which show considerable structure and connect the interstellar medium (ISM, the gas between the stars) within the galaxy disk to the surrounding environment. The evidence is mounting that these halos are dynamic entities; that is, they manifest the expulsion of dust, gas (ionized, neutral and molecular), cosmic rays, and magnetic fields from galaxy disks. What is not yet clear is how many and what type of galaxy is more likely to display such halos, how much expelled material cycles back to the disk again, and how much material leaves the galaxy, enriching the intergalactic medium (IGM, the low density gas between galaxies). We know that such outflows (or `feedback') play a crucial role in the formation of galaxies, yet the nature and details of this activity are not well known. The evidence suggests that galaxy evolution (including that of our own Milky Way) is strongly influenced by such activity, yet we do not even know the main drivers of such activity.