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 _ { N 6822 } = 7.5 ^ { +4.5 } _ { -0.1 } \times 10 ^ { 9 } M _ { \odot } and ( M / L ) _ { N 6822 } = 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 .