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Paper: Tracers of Extra-planar Gas and the Disk-Halo Connection
Volume: 331, Extra-Planar Gas
Page: 155
Authors: Dettmar, R.-J.
Abstract: Observations of diffuse ionized gas (DIG) in the halos of edge-on disk galaxies are discussed in reference to other tracers of extra-planar gas. The presence of DIG in the halo correlates well with star formation in the disk, corroborating the paradigm of a disk-halo connection with the interstellar medium driven by multiple and clustered supernovae. This is demonstrated using a survey of H+ halos with more than 70 objects. The survey allows us to establish a minimum energy release per unit area that is required to start the disk-halo mass exchange. The halo DIG is typically correlated with the presence of other gaseous phases and components of the ISM in the halo including hot X-ray gas, cosmic rays, and magnetic fields. The detection of extra-planar HII regions leads us to conclude that also molecular hydrogen must be present. From the polarization of synchrotron radio continuum maps a large scale and well ordered magnetic field in the gaseous halos can be deduced. Finally, we briefly discuss possible physical processes that lead to the formation of dusty structures in the disk-halo interface.
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