Abstract The presence of both the inner inner Lindblad resonance IILR and the outer inner Lindblad r

1
Evolution of Bar-driven Disks under the Influence
of the Interaction between Two Inner Lindblad
Resonances
Chi Yuan1 and David C.C. Yen1,2 1Institute of
Astronomy and Astrophysics, Academia Sinica,
Taiwan, R.O.C. 2Department of Mathematics, Fu-Jen
Catholic University, Hinchuang, Taipei Hsien,
Taiwan, R.O.C.
Abstract The presence of both the inner inner
Lindblad resonance (IILR) and the outer inner
Lindblad resonance (OILR) in a bar-driven
galactic disk highly complicates the
gas-dynamical processes in the disk and greatly
affects its structure and evolution. In this
study, we use the Antares codes to simulate the
evolution of the such disks. The Antares codes
are higher order Godunov codes we have developed,
which are featured with exact Riemann solver, the
self-gravitation of the disk, and the
non-reflection boundary conditions. There are
three important results (1) The resonance effect
spreads substantially beyond the maximum pattern
speed, which is tangent to the
curve, and hence beyond which there is no
resonance. (2) For the case of self-gravitation,
structural features in close resemblance with x1
and x2 orbits appear. (3) But in the case without
self-gravitation, no x1 and x2 orbital features.
The interaction of IILR and OILR produces a gas
bar aligned with and therefore reinforcing the
imposed bar. We will show results in movies. The
work is in parts supported by a grant from
National Science Council, Taiwan,
NSC94-2752-M-001-002-PAE.
Antares Code Two-dimensional high-order Godunov
codes based on the exact Riemann solver, and
featured with second order Poisson solver for
disk self-gravitation and with characteristics
decomposition to guarantee no reflection on the
boundary.
Axisymmetric Model We adopt the Elmegreen
rotation curve, with which the angular velocity
curve is depicted below. The
curve has a plateau, under which there are two
Lindblad resonances, the outer inner and the
inner inner (OILR and IILR) and above which no
resonance in the computing domain. The bar force
and initial density of the gas are also depicted.
Bar Force
Lindblad Resonance
Rotation Curve
Bell-Shape Density
Bar Orientation
Case of no resonance Bar speed from left to
right 25,30,35,40,50 km/s-kpc Resonance effect
remains despite of no resonance, tapering off at
high speeds.
Evolution IILR-OILR inter-action, 1-5 turns, bar
speed 15 km/s-kpc. No self-gravity. Gas forms a
bar aligning with the imposed bar,
eventually concentrated in the center.
Evolution IILR-OILR inter- action at 1-5 turns of
the bar, rotating speed 21 km/s-kpc,
no self-gravitation. Gas spirals turn from
leading to trailing. Gas bar parallel to the
imposed bar.
Double Ring Instability Same as above, except
self- gravity for the disk. Double rings form in
resemblance to x1 x2 orbits. Toomre
instability results after 4 turns of the bar.
Conclusion IILR adds amazing changes to the case
of single resonance at OILR. The interaction
results in bar-type responses aligned the
imposed bar. (1) When the two resonances are
more separate, like the case 15
km/s-kpc, a large gas bar forms, similar to the
case of major bar galaxies. (2) When IILR OILR
are close, 21 km/s-kpc, the last two
cases, there are major differences between with
and without self-gravity. For the without, it is
similar to case (1). But for the case with
self-gravity, double rings form, in resemblance
to x1 and x2 orbits in stellar dynamics. The
outer ring x1 displays Toomre type of
instability. (3) Resonance effect spreads beyond
the resonance point. For the case of no
resonance, as long as the bar speed is not too
large, the gas response remains similar to the
resonance case.