Galaxy Flybys: Evolution of the Bulge, Disk, and Spiral Arms
  Galaxy flybys are as common as mergers in low redshift universe and are
important for galaxy evolution as they involve the exchange of significant
amounts of mass and energy. In this study we investigate the effect of minor
flybys on the bulges, disks, and spiral arms of Milky Way mass galaxies for two
types of bulges - classical bulges and boxy/peanut pseudobulges. Our N-body
simulations comprise of two disk galaxies of mass ratios 10:1 and 5:1, where
the disks of the galaxies lie in their orbital plane and the pericenter
distance is varied. We performed photometric and kinematic bulge-disk
decomposition at regular time steps and traced the evolution of the disk size,
spiral structure, bulge sersic index, bulge mass, and bulge angular momentum.
Our results show that the main effect on the disks is disk thickening, which is
seen as the increase in the ratio of disk scale height to scale radius. The
strength of the spiral structure A2/A0 shows small oscillations about the mean
time-varying amplitude in the pseudobulge host galaxies. The flyby has no
significant effect on non-rotating classical bulge, which shows that these
bulges are extremely stable in galaxy interactions. However, the pseudobulges
become dynamically hotter in flybys indicating that flybys may play an
important role in accelerating the rate of secular evolution in disk galaxies.
This effect on pseudobulges is a result of their rotating nature as part of the
bar. Also, flybys do not affect the time and strength of bar buckling.
