On the Ionizing Sources in Spiral Galaxies: I. From Central Regions to   Thick Disk and Disk-Halo Connection
  We study the ionizing sources in spiral galaxies and examine in more detail our Galaxy. Using Taylor & Cordes (1993) model we analyze the electron density in different parts of the Galaxy, and emphasize the still unsolved problems. Finally, we compare the intensities of H$\alpha$ emission in disk and halo. 
S. Samurovic, M. M. Cirkovic, V. Milosevic-Zdjelar and J. Petrovic