Chemical enrichment by massive stars |
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| Institution: | 1. Main Astronomical Observatory, Ukrainian National Academy of Sciences, Goloseevo, 03680 Kiev-127, Ukraine;2. Astronomy Department, University of Virginia, Charlottesville, VA 22903, USA;1. Laboratory for Space Sciences and the Physics Department, Washington University, One Brookings Drive, St. Louis, MO 63130, USA;2. Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW Washington DC, 20015, USA;3. Max-Planck-Institut für Chemie, Kosmochemie, P.O. Box 3060, D-55020 Mainz, Germany;4. Dipartimento di Fisica Generale, Università di Torino, Via P. Giuria 1, I-10125 Torino, Italy;5. Centre for Stellar and Planetary Astrophysics, School of Mathematical Sciences, Monash University, Victoria 3800 Australia;6. INAF, Osservatorio Astronomico di Teramo, Italy;1. Centre for Astrophysics, University of Sciences & Technology of China, Hefei 230026 China;2. Shaanxi Observatory, Chinese Academy of Sciences, Lintong 710600 China;1. Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA;2. Department of Physics, Utkal University, Bhubaneswar 751004, India;3. Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, USA;4. Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA;5. Laboratoire d Astrophysique de Marseille, OAMP, UniversiteAix-Marseillé and CNRS, 13388 Marseille cedex 13, France;1. Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden;2. DARK, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø, Denmark;3. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA;1. Max-Planck-Institut für Astrophysik, D-85740 Garching, Germany |
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| Abstract: | Heavy element abundances derived from high-quality ground-based and Hubble Space Telescope (HST) spectroscopic observations of low-metallicity blue compact galaxies (BCGs) with oxygen abundances 12+log O/H between 7.1 and 8.3 are discussed. None of the heavy element-to-oxygen abundance ratios studied here (C/O, N/O, Ne/O, Si/O, S/O, Ar/O, Fe/O) depend on oxygen abundance for BCGs with 12+log O/H≤7.6 (Z≤Z⊙/20). This constancy implies that all these heavy elements have a primary origin and are produced by the same massive (M≥10 M⊙) stars responsible for O production. The dispersion of the C/O and N/O ratios in these galaxies is found to be remarkably small, being only ±0.03 dex and ±0.02 dex respectively. This very small dispersion is strong evidence against any time-delayed production of C and primary N in the lowest-metallicity BCGs, and hence against production of these elements by intermediate-mass (3 M⊙≤M≤9 M⊙) stars at very low metallicities, as commonly thought.In higher metallicity BCGs (7.6<12+log O/H<8.2), the Ne/O, Si/O, S/O, Ar/O and Fe/O abundance ratios retain the same constant value they had at lower metallicities. By contrast, there is an increase of the C/O and N/O ratios along with their dispersions at a given O. We interpret this increase as due to the additional contribution of C and primary N production in intermediate-mass stars, on top of that by high-mass stars. BCGs show the same O/Fe overabundance with respect to the Sun (～0.4 dex) as galactic halo stars, suggesting the same chemical enrichment history. |
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