Dark Matter Halos and Evolution of Bars in Disk Galaxies: Varying Gas
  Fraction and Gas Spatial Resolution
  We conduct numerical experiments by evolving gaseous/stellar disks embedded
in live dark matter halos aiming at quantifying the effect of gas spatial
resolution and gas content on the bar evolution. Model sequences have been
constructed using different resolution, and gas fraction has been varied along
each sequence within fgas=0%-50%, keeping the disk and halo properties
unchanged. We find that the spatial resolution becomes important with an
increase in `fgas'. For the higher resolution model sequences, we observe a
bimodal behavior in the bar evolution with respect to the gas fraction,
especially during the secular phase of this evolution. The switch from the
gas-poor to gas-rich behavior is abrupt and depends on the resolution used. The
diverging evolution has been observed in nearly all basic parameters
characterizing bars, such as the bar strength, central mass concentration,
vertical buckling amplitude, size, etc. We find that the presence of the gas
component severely limits the bar growth and affects its pattern speed
evolution. Gas-poor models display rapidly decelerating bars, while gas-rich
models exhibit bars with constant or even slowly accelerating tumbling. The
gas-rich models have bar corotation (CR) radii within the disk at all times, in
constrast with gas-poor and purely stellar disks. The CR-to-bar size ratio is
less than 2 for gas rich-models. We have confirmed that the disk angular
momentum within the CR remains unchanged in the gas-poor models, as long as the
CR stays within the disk, but experiences a sharp drop before leveling off in
the gas-rich models. Finally, we discuss a number of observed correlations
between various parameters of simulated bars, e.g., bar sizes and gas
fractions, bar strength and buckling amplitude, bar strength and its size, etc.
