Exploration of the physical conditions of gas in Local Group halos

我们建议研究本星系群内的中性气体。世界上最大的全可控射电望远镜已经被我们用来准备银河I的全天调查。凭借Effelsberg-Bonn HI巡天（EBHIS）和Parkes银河全天巡天（GASS）前所未有的灵敏度，可以在本星系群的“边缘”（1Mpc）探测到质量低于M≤2.104 M⊙的HI云。现在我们打算利用这些数据来探索整个天空中的矮星系、紧凑的高速云和高速云复合体的环境和物理状态。这包括面外气体，我们可以在pc尺度上解析结构。这些天体都属于银河晕，但它们暴露在不同的环境条件下：最重要的是电离辐射场和银河系引力场内的运动学情况。我们打算将我们之前的调查扩展到整个天空，以便对高速的高天体进行公正的普查。这包括星系的吸积历史，多相日冕气体的组成，由湍流和热不稳定性引起的相变以及与磁场的相互作用。我们建议在高速下建立一个全面的星际介质数据库，目的是评估其物理性质，并在小尺度和大尺度上追踪星际介质的演化。

We propose to study the neutral gas within the Local Group of Galaxies. The world’s largest fully-steerable radio telescopes of both hemispheres have been used by us to prepare Galactic H I all-sky surveys. With the unprecedented sensitivity of the Effelsberg–Bonn HI Survey (EBHIS) and the Parkes Galactic All–Sky Survey (GASS) it gets possible to detect HI clouds with masses down to M ≤ 2•104 M⊙ at the “rim” (1Mpc) of the Local Group. Now we intend to use these data to explore all over the sky the environments and physical states of dwarf galaxies, compact high–velocity clouds and high–velocity cloud complexes. This includes the extraplanar gas where we can resolve structures on pc scales. Such objects belong all to the Galactic halo but they are exposed to different environmental conditions: most important are the ionizing radiation field and the kinematical situation within the gravitational field of the Milky Way. We intend to extend our previous investigations all over the sky for an unbiased census of HI objects at high velocities. This includes the accretion history of galaxies, the composition of the multiphase coronal gas, phase transitions induced by turbulence and thermal instabilities and interactions with the magnetic field. We propose to generate a comprehensive data base of the ISM at high velocities with the aim to evaluate the physical properties and to trace the evolution of the interstellar medium on small as well as large scales.