The Distribution of Warm Ionized Medium in Galaxies
  Ionized nebulae have been targets of interest since the introduction of the
telescope centuries ago. These isolated, "classical" H II regions gave us some
of the earliest insight into the copious feedback energy that stars inject into
the interstellar medium. Their unique spectra contain information about the
quality and quantity of the ionizing field as well as the temperature, density,
and metallicity of these discrete locations in the Galaxy. With increasing
sensitivity across many spectral domains, we now know that ionized gas is not
localized to massive star regions in many star-forming galaxies. In particular,
recent observational studies allow a thorough comparison of the physical
conditions and distribution of the well-studied classical H II regions to the
more widespread warm, diffuse gas. By more realistically evolving a dynamic
interstellar medium, models are beginning to reproduce the observed emission
measure variations and provide a natural solution to the propagation of
ionizing flux from a predominantly neutral galactic disk to the distant halo.
