Bibcode
Morales-Luis, A. B.; Sánchez-Almeida, J.; Pérez Montero, E.; Muñoz-Tuñon, C.; Aguerri, J. A. L.; Vilchez, J. M.; Terlevich, E.; Terlevich, R.
Referencia bibliográfica
Highlights of Spanish Astrophysics VII, Proceedings of the X Scientific Meeting of the Spanish Astronomical Society (SEA), held in Valencia, July 9 - 13, 2012, Eds.: J.C. Guirado, L.M. Lara, V. Quilis, and J. Gorgas., pp.294-299
Advertised on:
5
2013
Número de citas
2
Número de citas referidas
2
Descripción
The determination of oxygen abundance in nebulae requires measuring a
significant number of emission lines distributed along a wide spectral
range. The required measurements are hard to obtain at high redshift,
where sources are very faint, and where the accessible spectral range is
limited. These difficulties are often overcome using empirical
relationships between the oxygen abundance and the fluxes in a small
number of strong lines. The so-called strong-line methods are often the
only practical alternative for metallicity estimate at high redshift.
In this sense, the low metallicities range is particularly important
since high redshift objects are primitive and so of low metallic
content. One of the most widely used relationships links the oxygen
with the ratio between [NII]6583 and Hα. This relationship shows a
large scatter at low metallicity. In an effort to bring down the
errors, we re-calibrated the relationship using a large sample of
extremely metal-poor galaxies. The SDSS spectra of the galaxies were
all analyzed in the same way to minimize systematic errors. To our
surprise, the decrease of scatter reveals that the ratio [N{II}]6583 to
Hα seems to be independent of metallicity at low oxygen abundance
(12+log[{O}/{H}] < 7.6). This result casts doubts on the
metallicities of high-redshift objects based on the relationship. We
explain how the re-calibration was carried (including the sample
selection and the abundance determinations). In addition, we try explain
what produces the lack of correlation.