EAS Publications Series
Volume 56, 2012The Role of the Disk-Halo Interaction in Galaxy Evolution: Outflow vs. Infall?
|Page(s)||213 - 220|
|Section||Evidence for a Disk-Halo Connection in Galaxies|
|Published online||17 September 2012|
Miguel A. de Avillez (ed)
EAS Publications Series, 56 (2012) 213–220
Diffuse Ionized Gas in Spiral Galaxies and the Disk-Halo Interaction
1 Astronomy Department, University of Wisconsin, Madison, WI 53706, USA
2 School of Physics, The University of Sydney, NSW 2006, Australia
3 School of Physics and Astronomy, University of St. Andrews, Scotland
Thick layers of warm, low density ionized hydrogen (i.e., the warm ionized medium or WIM) in spiral galaxies provide direct evidence for an interaction between the disk and halo. The wide-spread ionization implies that a significant fraction of the Lyman continuum photons from O stars, produced primarily in isolated star forming regions near the midplane and often surrounded by opaque clouds of neutral hydrogen, is somehow able to propagate large distances through the disk and into the halo. Moreover, even though O stars are the source of the ionization, the temperature and ionization state of the WIM differ significantly from what is observed in the classical O star H ii regions. Therefore, the existence of the WIM and observations of its properties provide information about the structure of the interstellar medium and the transport of energy away from the midplane as well as place significant constraints on models.
© EAS, EDP Sciences, 2012