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Session 54 - Spiral Galaxy Kinematics.
Oral session, Tuesday, January 14
The photometric and kinematic structure of barred galaxies is complex; gas in bars shows strongly non-circular streaming motions. These non-axisymmetric motions respond directly to the mass of the luminous bar. This presents an opportunity to lift the ``maximum disk'' degeneracy of tradeoff of luminous disk mass against dark halo mass, encountered in fitting rotation curves of axisymmetric disk galaxies. Fully two-dimensional velocity fields with high spatial and velocity resolution are required to map the non-circular kinematics, and the gas flow pattern shows evidence of shocks within the bar and therefore requires fluid-dynamical modeling. We can constrain parameters of a bar, such as the M/L and pattern speed, by running gas-dynamical computations for a variety of models of the galaxy potential.
We present 2-D velocity fields from Fabry-Perot H\alpha and VLA 21\,cm observations of barred galaxies. We compare to fluid-dynamical computations of the gas flow which use model potentials derived from I-band photometry, to determine the M/L and pattern speeds of the bars. We additionally use gas-dynamical models to constrain parameters of the Milky Way bar, by comparison with the 21\,cm data of Liszt amp; Burton (1980).
Program listing for Tuesday