Extended Star Clusters in the Remote Halo of the Intriguing Dwarf Galaxy
  NGC 6822
  We present a study on four new star clusters discovered in the halo of the
intriguing dwarf irregular galaxy NGC 6822 from a wide field survey covering 3
deg x 3 deg area carried out with MegaCam at Canada-France-Hawaii Telescope
(CFHT). The star clusters have extended structures with half-light radii R_h ~
7.5 -- 14.0 pc, larger than typical Galactic globular clusters and other known
globular clusters in NGC 6822. The integrated colors and color magnitude
diagrams (CMD) of resolved stars suggest that the new star clusters are 2 -- 10
Gyr old and relatively metal poor with Z=0.0001--0.004 based on the comparison
with theoretical models. The projected distance of each star cluster from the
galaxy center ranges from 10.7 arcmin (~ 1.5 kpc) to 77 arcmin (~ 11 kpc), far
beyond the optical body of the galaxy. Interestingly, the new star clusters are
aligned along the elongated old stellar halo of NGC 6822, which is almost
perpendicular to the HI gas distribution where young stellar populations exist.
We also find that the colors and half-light radii of the new clusters are
correlated with the galactocentric distance: clusters farther from the galaxy
center are larger and bluer than those closer to the galaxy center. We discuss
the stellar structure and evolution of NGC 6822 implied by these new extended
star clusters in the halo. We also discuss the current status of observational
and theoretical understandings regarding the origin of extended star clusters
in NGC 6822 and other galaxies.
