Session 54 - Spiral Galaxy Kinematics.
Oral session, Tuesday, January 14
Harbour B,

## [54.01] Structure and Dynamics of Barred Spiral Galaxies

B. J. Weiner, J. A. Sellwood, T. B. Williams (Rutgers), J. H. van Gorkom (Columbia)

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).