Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pasj...46..165w&link_type=abstract
PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264), vol. 46, no. 2, p. 165-172
Astronomy and Astrophysics
Astronomy
56
Astronomical Models, Celestial Mechanics, Galactic Structure, Gravitational Fields, Hydrodynamics, Mathematical Models, Orbital Resonances (Celestial Mechanics), Potential Fields, Spiral Galaxies, Elliptical Orbits, Equations Of Motion, Gas Dynamics, Harmonic Oscillators, Phase Shift
Scientific paper
We provide an analytical model which represents the behavior of a non-self-gravitating gas in a rotating potential with a weak bar-like distortion. The gas dynamics can be understood in terms of closed elliptical orbits which are solutions to the equations of motion of a damped oscillator driven by a periodic external force. Gaseous elliptical orbits always incline to the bar potential in a leading sense inside of the corotation, and in a following sense outside of the corotation. If there are two inner Lindblad resonances (ILRs), the gas orbits at the ILRs are oriented by 45 deg with respect to the bar potential. The damped orbits gradually change their orientation with their radius. Since the direction of the gradual rotation near to the first ILR and that near to the second ILR are in an opposite sense, leading or trailing spiral-like enhancements appear near to the first and the second ILR, respectively. This gradual rotation is explained in terms of the phase-shift of a damping oscillator. Our analytical model well describes the gas behavior seen in hydrodynamical simulations. The damped-orbit model can also explain the leading gaseous bar which is often seen in self-gravitating gas simulations. We conclude that the particle (stellar) resonance-orbits based on an epicycle approximation is inadequate for interpreting the gaseous dynamics in a barred potential. Our analysis provides the basis for a physical understanding of the gas behavior in both numerical simulations and real galaxies.
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