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D.A. Kornreich (Ctr for Radiophysics and Space Res.), M.P. Haynes (Ctr for Radiophysics and Space Res. and Nat. Astronomy and Ionosphere Ctr), R.V.L. Lovelace (Cornell University), L. van Zee ()
Although most studies of spiral galaxy dynamics concentrate on understanding the properties of axisymmetric disks, evidence is accumulating that many galaxies lack such overall symmetry. Based on optical appearance, approximately 30% of field disk galaxies exhibit significant ``lopsidedness''(Rix & Zaritsky 1995; Kornreich et al. 1998, KHL). Moreover, Haynes et al. (1998) report that approximately 50% of disk galaxies exhibit asymmetries in their HI line profiles. That study also finds that the very optically lopsided galaxy NGC~1637 exhibits a symmetric profile, raising the question of how well unusual morphology correlates with disturbed kinematics. We are therefore undertaking a project to compare the lopsidedness of optical and gas distributions, to search for correlations between morphological and kinematic asymmetry, and to test possible long-lived asymmetry scenarios. Morphological asymmetry is measured by comparing radially-integrated fluxes in different sectors of the galaxy image, while dynamical asymmetry is measured by differences in rotation-curve fitting between the approaching and receding sides. We have conducted HI synthesis mapping of the galaxies NGC~991, NGC~1042, and UGC~3685, selected from the KHL optical sample of face--on spirals, at the VLA in the CS--configuration. Of the three, NGC~991, NGC~1042 were found to be non-axisymmetric by KHL. While the HI gas distributions are seen to follow the optical light within the optical radius, there are no systematic differences in distribution outside of the optical radius between the optically symmetric and asymmetric galaxies. We find no evidence for asymmetry (beyond warping beyond the optical radius) in the dynamics of any of the three galaxies. This result seems consistent with the findings of Haynes et al. We discuss possible reasons for a lack of correlation between optical and dynamical asymmetry and present plans for the expansion of this study to a larger sample.
The author(s) of this abstract have provided an email address for comments about the abstract: dkorn@alderan.tn.cornell.edu