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Session 54 - Spiral Galaxy Kinematics.
Oral session, Tuesday, January 14
Mass inflow in barred galaxies has been invoked to account for a wide variety of phenomena but until now no direct evidence for inflow has been available. We present Fabry-Perot H\alpha observations of the barred spiral galaxy NGC 1530 for which we determine velocities of the ionized gas for the entire region swept by the bar. We compare the velocity field to models of gas flow in barred spirals and show that it is well reproduced by ideal gas hydrodynamic models. Inspection of the models and observations reveals that gas entering the dust lanes streams directly down the dust lanes toward the 2 kpc radius nuclear ring. Approximately 20% of the gas flowing down the dust lane enters the nuclear ring; the remaining gas sprays around the ring to the other bar dust lane. The fraction of the gas entering the ring is relatively insensitive to the shape or size of the bar. Our observations of the velocity field and dust optical depth yield a mass inflow rate into the nuclear ring of 1 M_\sun yr^-1. We investigate two major sources of global torque that cause gas to lose angular momentum: gravitational torques of the stellar potential and hydrodynamic torques. From observational constraints and modelling, we determine that within the bar region both hydrodynamic and gravitational torques play a role. Even so, neither gravitational nor hydrodynamic torques can explain the radial gas profiles of the outer disks of spiral galaxies; we suggest the Balbus-Hawley magnetic instability as one possible torque which is consistent with the observations.
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