Abundance determination from global emission-line SDSS spectra: Exploring objects with high N/O ratios
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...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2012 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/423972 |
| Acceso en línea: | http://hdl.handle.net/10261/423972 |
| Access Level: | acceso abierto |
| Palabra clave: | ISM: abundances H II regions Galaxies: abundances |
| Sumario: | 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 Hii 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 Hii 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 Hii 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 ~0.2dex. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. |
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