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J. A. Collins, R. J. Rand (University of New Mexico), R. Benjamin (University of Wisconsin)
Using spectroscopic data for the edge-on galaxy NGC 5775, we have obtained velocity centroids of the H\alpha, [\ion{N}{2}]\lambda6583, and [\ion{S}{2}]\lambda6716 lines for two slit positions oriented perpendicular to the plane. These data then provide the first substantial information on halo rotation well above the midplane, and in the case of one slit, up to z\approx13 kpc. A general trend of a change in heliocentric velocity towards systemic with z is observed indicating a decrease in rotation velocity with height above the midplane, with very little rotation at highest z observed. We present results of comparisons to models of the vertical velocity gradient, including a model where clouds take ballistic trajectories from the disk to halo. We discuss implications of these results for topics such as support mechanisms of gaseous layers, the transfer of angular momentum from disk to halo, and the radial redistribution of gas through disk-halo cycling.
This work was partially supported by NSF grant AST-9986113.