A Study of the Effect of Bulges on Bar Formation in Disk galaxies
  We use N-body simulations of bar formation in isolated galaxies to study the
effect of bulge mass and bulge concentration on bar formation. Bars are global
disk instabilities that evolve by transferring angular momentum from the inner
to outer disks and to the dark matter halo. It is well known that a massive
spherical component such as halo in a disk galaxy can make it bar stable. In
this study we explore the effect of another spherical component, the bulge, on
bar formation in disk galaxies. In our models we vary both the bulge mass and
concentration. We have used two sets of models, one that has a dense bulge and
high surface density disk. The second model has a less concentrated bulge and a
lighter disk. In both models we vary the bulge to disk mass fraction from 0 to
0.7. Simulations of both the models show that there is an upper cutoff in bulge
to disk mass ratio M b /M d above which bars cannot form; the cutoff is smaller
for denser bulges( M b /M d = 0.2) compared to less denser ones (M b /M d =
0.5). We define a new criteria for bar formation in terms of bulge to disk
radial force ratio (F b /F d ) at the disk scale lengths above which bars
cannot form. We find that if F b /F d > 0.35, a disk is stable and a bar cannot
form. Our results indicate that early type disk galaxies can still form strong
bars in spite of having massive bulges.
