Journal
ASTROPHYSICAL JOURNAL
Volume 829, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/0004-637X/829/2/70
Keywords
galaxies: distances and redshifts; galaxies: individual (NGC 55); stars: early-type; supergiants
Categories
Funding
- National Science Foundation [AST-1008789, AST-1108906]
- Munich Institute for Astro- and Particle Physics (MIAPP) of the DFG cluster of excellence Origin and Structure of the Universe
- BASAL Centro de Astrofisica y Tecnologias Afines (CATA) [PFB-06/2007]
- Millennium Institute of Astrophysics (MAS) of the Iniciativa Cientifica Milenio del Ministerio de Economia, Fomento y Turismo de Chile [IC120009]
- Ideas Plus grant of the Polish Ministry of Science and Higher Education
- Foundation for Polish Science (FNP)
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Low-resolution (4.5-5 angstrom) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques to determine stellar temperatures, gravities, and metallicities (from iron peak and a-elements). A metallicity gradient of -0.22 +/- 0.06 dex/R-25 is detected. The central metallicity on a logarithmic scale relative to the Sun is [Z] = -0.37 +/- 0.03. A chemical evolution model using the observed distribution of column densities of the stellar and interstellar medium gas mass reproduces the observed metallicity distribution well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extraplanar metal-poor H II regions detected in previous work 1.13 to 2.22 kpc above the galactic plane are ionized by massive stars formed in situ outside the disk. For a subsample of supergiants, for which Hubble Space Telescope photometry is available, the flux-weighted gravity-luminosity relationship is used to determine a distance modulus of 26.85 +/- 0.10 mag.
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