On the origin of gaseous galaxy halos - Low-column density gas in the
  Milky Way halo
  Recent observations show that spiral galaxies are surrounded by extended
gaseous halos as predicted by the hierarchical structure formation scenario.
The origin and nature of extraplanar gas is often unclear since the halo is
continuously fueled by different circulation processes as part of the on-going
formation and evolution of galaxies (e.g., outflows, galaxy merging, and gas
accretion from the intergalactic medium). We use the Milky Way as a laboratory
to study neutral and mildly ionised gas located in the inner and outer halo.
Using spectral line absorption and emission measurements in different
wavelength regimes we obtain detailed information on the physical conditions
and the distribution of the gas. Such studies are crucial for our understanding
of the complex interplay between galaxies and their gaseous environment as part
of the formation and evolution of galaxies. Our analysis suggests that the
column-density distribution and physical properties of gas in the Milky Way
halo are very similar to that around other disk galaxies at low and high
redshifts.
