Spectroscopic study of extended star clusters in dwarf galaxy NGC 6822

Journal Article · Sat Mar 01 04:00:00 EST 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/783/1/49· OSTI ID:22351350

Hwang, Narae; Kim, Sang Chul ^[1]; Park, Hong Soo; Lee, Myung Gyoon; Lim, Sungsoon ^[2]; Hodge, Paul W.; Weisz, Daniel ^[3]; Miller, Bryan ^[4]

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1. Korea Astronomy and Space Science Institute, 776 Daedeokdae-Ro Yuseong-Gu, Daejeon 305-348 (Korea, Republic of)
2. Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of)
3. Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States)
4. Gemini Observatory, Casilla 603, La Serena (Chile)

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 ± 20.4 km s{sup –1} (for C1) to –115.34 ± 57.9 km s{sup –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 (≥8 Gyr) and metal poor ([Fe/H] ≲ –1.5). NGC 6822 is found to have both metal poor ([Fe/H] ≈–2.0) and metal rich ([Fe/H] ≈–0.9) star clusters within 15' (2 kpc) from the center, whereas only metal poor clusters are observed in the outer halo with r ≥ 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{sub −0.1}{sup +4.5}×10{sup 9} M{sub ⊙} and (M/L){sub N6822}=75{sub −1}{sup +45}(M/L){sub ⊙}. It shows that NGC 6822 is one of the most dark matter dominated dwarf galaxies in the Local Group.

• OSTI ID: 22351350
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 783; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON STARS
DISTRIBUTION
GALAXIES
MASS
METALLICITY
NONLUMINOUS MATTER
RADIAL VELOCITY
ROTATION
SPECTRA
STAR CLUSTERS
TELESCOPES
VISIBLE RADIATION