Modern view of the warm ionized medium
  We review the observational evidence that the warm ionized medium (WIM) is a major and physically distinct component of the Galactic interstellar medium. Although up to ~20% of the faint, high-latitude H-alpha emission in the Milky Way may be scattered light emitted in midplane H II regions, recent scattered light models do not effectively challenge the well-established properties of the WIM. 
A. S. Hill, R. J. Reynolds, L. M. Haffner, K. Wood, G. J. Madsen
astro-ph.GA