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 the Gemini Multi-Object Spectrograph on the Gemini-South 8.1 m telescope. The radial velocities derived from the spectra range from -61.2 + or - 20.4 km s super(-1) (for C1) to - 11...

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Bibliographic Details
Published in:The Astrophysical journal 2014-03, Vol.783 (1), p.1-10
Main Authors: HWANG, NARAE, Park, Hong Soo, Lee, Myung Gyoon, Lim, Sungsoon, Hodge, Paul W, Kim, Sang Chul, Miller, Bryan, Weisz, Daniel
Format: Article
Language:English
Subjects:
Age
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
CARBON STARS
DISTRIBUTION
Dwarf galaxies
GALAXIES
Halos
Iron
MASS
METALLICITY
NONLUMINOUS MATTER
RADIAL VELOCITY
ROTATION
SPECTRA
Spectroscopic analysis
Spectroscopy
STAR CLUSTERS
TELESCOPES
VISIBLE RADIATION
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Summary:We present a spectroscopic study of the four extended star clusters (ESCs) in NGC 6822 based on the data obtained with the Gemini Multi-Object Spectrograph on the Gemini-South 8.1 m telescope. The radial velocities derived from the spectra range from -61.2 + or - 20.4 km s super(-1) (for C1) to - 115.34 + or - 57.9 km s super(-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 ([> or =, slanted]8 Gyr) and metal poor ([Fe/H] [lap] -1.5). NGC 6822 is found to have both metal poor ([Fe/H] approximately -2.0) and metal rich ([Fe/H] approximately -0.9) star clusters within 15' (2 kpc) from the center, whereas only metal poor clusters are observed in the outer halo with r [> or =, slanted] 20'(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 sub(N6822) = 7.5 super(+45) sub(-1), x 10 super(9) M sub([middotcircle]) and (M/L) sub(N6822) = 75 super(+45) sub(-1)(M /L) sub([middotcircle]). It shows that NGC 6822 is one of the most dark matter dominated dwarf galaxies in the Local Group.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/783/1/49