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3.4. Discussion

This first large Halpha survey of edge-on galaxies has shown that eDIG is a general phenomenon only for galaxies which exceed a minimal threshold of SF activity. As already suggested by Rand (1996) and Rossa & Dettmar (2000), the results presented in this work corroborate this view that a considerable fraction of late-type spirals indeed show extended DIG emission in their galactic halos. Although not as common as in starburst galaxies eDIG is a widespread phenomenon and is not a characteristic belonging only to a small fraction of late-type spirals. For details concerning the interpretation of our data we refer to Rossa & Dettmar (2003, Paper I).

Evidence for the disk-halo interaction has also been gathered from observations tracing other constituents of the ISM, such as the hot ionized medium (HIM) (Dahlem, 1997; Bregman & Pildis, 1994), and dust (Howk & Savage, 1999). The latter constituent is also briefly discussed for our survey galaxies in the following section.