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Ca ɪɪ triplet spectroscopy of RGB stars in NGC 6822: kinematics and metallicities


Swan, J and Cole, AA and Tolstoy, E and Irwin, MJ, Ca ɪɪ triplet spectroscopy of RGB stars in NGC 6822: kinematics and metallicities, Monthly Notices of the Royal Astronomical Society, 456, (4) pp. 4315-4327. ISSN 0035-8711 (2016) [Refereed Article]


Copyright Statement

Copyright 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

DOI: doi:10.1093/mnras/stv2774


We present a detailed analysis of the chemistry and kinematics of red giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at ≈8500 Ĺ was acquired for 72 red giant stars across two fields using FORS2 at the VLT. Line-of-sight extinction was individually estimated for each target star to accommodate the variable reddening across NGC 6822. The mean radial velocity was found to be 〈υrad〉 = −52.8 ± 2.2 km s−1 with dispersion συ = 24.1 km s−1, in agreement with other studies. Ca ɪɪ triplet equivalent widths were converted into [Fe/H] metallicities using a V magnitude proxy for surface gravity. The average metallicity was 〈[Fe/H]〉 = −0.84 ± 0.04 with dispersion σ = 0.31 dex and interquartile range 0.48. Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal-rich and metal-poor stars; the former were found to cluster towards small radii with the metal-poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal-poor stars was found to be higher than that of the metal-rich stars (συMP = 27.4 km s−1; συMR = 21.1 km s−1); combined with the age–metallicity relation this indicates that the older populations have either been dynamically heated during their lifetimes or were born in a less disc-like distribution than the younger stars. The low ratio υrotυ suggests that within the inner 10 arcmin, NGC 6822's stars are dynamically decoupled from the H ɪ gas, and possibly distributed in a thick disc or spheroid structure.

Item Details

Item Type:Refereed Article
Keywords:galaxies: abundances, galaxies: dwarf, galaxies: irregular, galaxies: kinematics and dynamics, galaxies: stellar content
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Galactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Swan, J (Mr Jesse Swan)
UTAS Author:Cole, AA (Professor Andrew Cole)
ID Code:107645
Year Published:2016
Web of Science® Times Cited:12
Deposited By:Mathematics and Physics
Deposited On:2016-03-21
Last Modified:2017-11-01
Downloads:169 View Download Statistics

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