Exploration of the physical conditions of gas in Local Group halos

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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.