Kinematic imprint of clumpy disk formation on halo objects
  Context: Clumpy disk galaxies in the distant universe, at redshift of z>1,
have been observed to host several giant clumps in their disks. They are
thought to correspond to early formative stages of disk galaxies. On the other
hand, halo objects, such as old globular clusters and halo stars, are likely to
consist of the oldest stars in a galaxy (age>10 Gyr), therefore the clumpy disk
formation can be presumed to take place in a pre-existing halo system. Aims:
Giant clumps are orbiting in the same direction in a premature disk and so
massive that they may be expected to interact gravitationally with halo objects
and exercise influence on kinematic state of the halo. Accordingly, I
scrutinize the possibility that the clumps leave a kinematic imprint of the
clumpy disk formation on a halo system. Methods: I perform a restricted N-body
calculation with a toy-model to study the kinematic influence on a halo by
orbital motions of clumps, examine dependence of the results on masses
(mass-loss), number and orbital radii of the clumps. Results: I will show that
halo objects can catch clump motions and acquire disky rotation in a dynamical
friction time-scale of the clumps, ~0.5 Gyr. The influence of clumps is limited
within a region around the disk, the halo system shows vertical gradients of
net rotation velocity and orbital eccentricity. The significance of the
kinematic influence strongly depends on the clump masses, the lower limit of
postulated clump mass would be 5x10^8 solar masses. The result depends also on
whether the clumps are subjected to rapid mass-loss or not, which is an open
question under debate in recent studies. The existence of such massive clumps
is not unrealistic, I therefore suggest that there could remain the imprints of
past clumpy disk formation in current galactic halos.
