Spectroscopic Study of Extended Star Clusters in Dwarf Galaxy NGC 6822
  We present a spectroscopic study of the four extended star clusters (ESCs) in
NGC 6822 based on the data obtained with Gemini Multi-Object Spectrograph
(GMOS) on the Gemini-South 8.1m telescope. Their radial velocities derived from
the spectra range from $-61.2 \pm 20.4$ km s$^{-1}$ (for C1) to $-115.34 \pm
57.9$ km s$^{-1}$ (for C4) and, unlike the intermediate age carbon stars, they
do not display any sign of systematic rotation around NGC 6822. The ages and
metallicities derived using the Lick indices show that the ESCs are old ($\geq
8$ Gyr) and metal poor ([Fe/H]$\lesssim -1.5$). NGC 6822 is found to have both
metal poor ([Fe/H]$\approx -2.0$) and metal rich ([Fe/H]$\approx -0.9$) star
clusters within 15 arcmin (2 kpc) from the center, while only metal poor
clusters are observed in the outer halo with $r \geq 20$ arcmin (2.6 kpc). The
kinematics, old ages, and low metallicities of ESCs suggest that ESCs may have
accreted into the halo of NGC 6822. Based on the velocity distribution of ESCs,
we have determined the total mass and the mass-to-light ratio of NGC 6822:
$M_{N6822} = 7.5^{+4.5}_{-0.1} \times 10^{9} M_{\odot}$ and $(M/L)_{N6822} =
75^{+45}_{-1} (M/L)_{\odot}$. It shows that NGC 6822 is one of the most dark
matter dominated dwarf galaxies in the Local Group.
