期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 421, 期 2, 页码 1624-1634出版社
WILEY-BLACKWELL
DOI: 10.1111/j.1365-2966.2012.20420.x
关键词
ISM: abundances; H II regions; galaxies: abundances
资金
- Ministerio de Education of Spain [SAB2010-0054]
- National Academy of Sciences of Ukraine
- Spanish PNAYA [AYA2010-21887-C04-01]
- MICINN [CSD2006-00070]
- Danish National Research Foundation
- Alfred P. Sloan Foundation
- National Science Foundation
- US Department of Energy
- National Aeronautics and Space Administration
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
- American Museum of Natural History
- Astrophysical Institute Potsdam
- University of Basel
- University of Cambridge
- Case Western Reserve University
- University of Chicago
- Drexel University
- Fermilab
- Institute for Advanced Study
- Japan Participation Group
- Johns Hopkins University
- Joint Institute for Nuclear Astrophysics
- Kavli Institute for Particle Astrophysics and Cosmology
- Korean Scientist Group
- Chinese Academy of Sciences (LAMOST)
- Los Alamos National Laboratory
- Max-Planck-Institute for Astronomy (MPIA)
- Max-Planck-Institute for Astrophysics (MPA)
- New Mexico State University
- Ohio State University
- University of Pittsburgh
- University of Portsmouth
- Princeton University
- United States Naval Observatory
- University of Washington
We have compared the oxygen and nitrogen abundances derived from global emission-line Sloan Digital Sky Survey (SDSS) spectra of galaxies using (1) the T-e method and (2) two recent strong-line calibrations: the ON and NS calibrations. Using the T-e method, anomalously high N/O abundance ratios have been found in some SDSS galaxies. To investigate this, we have Monte Carlo simulated the global spectra of composite nebulae by a mix of spectra of individual components, based on spectra of well-studied H II regions in nearby galaxies. We found that the T-e method results in an underestimated oxygen abundance (and hence in an overestimated nitrogen-to-oxygen ratio) if H II regions with different physical properties contribute to the global spectrum of composite nebulae. This effect is somewhat similar to the small-scale temperature fluctuations in H II regions discussed by Peimbert. Our work thus suggests that the high T-e-based N/O abundance ratios found in SDSS galaxies may not be real. However, such an effect is not expected to be present in dwarf galaxies since they generally have a uniform chemical composition. The ON and NS calibrations give O and N abundances in composite nebulae which agree with the mean luminosity-weighted abundances of their components to within similar to 0.2 dex.
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