What is the Origin of the High-$z$ Gas in NGC 4631?
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Session 19 -- Gas and Star Formation in Spiral Galaxies
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [19.09] What is the Origin of the High-$z$ Gas in NGC 4631?

Richard J. Rand (Univ. of Maryland)

A high-resolution (12"x22") 21-cm study of the NGC 4631 group of galaxies has been carried out with the Westerbork Synthesis Radio Telescope. NGC 4631 is a late-type, disturbed edge-on galaxy with impressive radio continuum and X-ray halos which may owe their existence to gas ejected from the disk by star formation, and a pair of H$\alpha$ \lq\lq worms\rq\rq\ above the nuclear regions which may trace a blown out superbubble. This poster focuses on the nature and origin of HI far from the major axis of NGC 4631 and looks for evidence that the HI disk has been shaken up by star formation. Position-velocity diagrams are used extensively to examine: a) the two Supershells reported by Rand \& van der Hulst, b) the global vertical structure of the HI layer and whether star formation has lifted much gas far from the plane, and c) whether there is HI coincident with the high-$z$ radio continuum spurs and H$\alpha$ worms. The most important conclusion is that the large extent of the emission along the minor axis is mostly due to inclination effects, the large scale-height (500--1000 pc) of the outer disk material, and the region where a tidal spur joins onto the outer disk. The ragged appearance of the layer is thus an outer disk phenomenon. There are a few high-$z$ features in the inner disk which are probably gas lifted off the plane by star formation, but these contribute little to the overall vertical extent.