On the Use of the Index N2 to Derive the Metallicity in Metal-poor Galaxies

Morales-Luis, A. B.; Pérez-Montero, E.; Sánchez Almeida, J.; Muñoz-Tuñón, C.
Referencia bibliográfica

The Astrophysical Journal, Volume 797, Issue 2, article id. 81, 6 pp. (2014).

Fecha de publicación:
12
2014
Número de autores
4
Número de autores del IAC
3
Número de citas
25
Número de citas referidas
23
Descripción
The N2 index ([N II] λ6584/Hα) is used to determine emission line galaxy metallicities at all redshifts, including high redshift, where galaxies tend to be metal-poor. The initial aim of this work was to improve the calibrations used to infer oxygen abundance from N2 by employing updated low-metallicity galaxy databases. We compare N2 and the metallicity determined using the direct method for the set of extremely metal-poor galaxies compiled by Morales-Luis et al. To our surprise, the oxygen abundance presents a tendency to be constant with N2, with a very large scatter. Consequently, we find that the existing N2 calibrators overestimate the oxygen abundance for most low-metallicity galaxies, and can therefore only be used to set upper limits to the true metallicity in low-metallicity galaxies. An explicit expression for this limit is given. In addition, we try to explain the observed scatter using photoionization models. It is mostly due to the different evolutionary state of the H II regions producing the emission lines, but it also arises due to differences in N/O among the galaxies.
Proyectos relacionados
Imagen del Proyecto
Grupo de Estudios de Formación Estelar GEFE
El proyecto interno GEFE está enmarcado en el proyecto coordinado, ESTALLIDOS, financiado por el plan nacional desde el año 2001. El ultimo proyecto aprobado es ESTALLIDOS 6.0 (AYA2016- 79724-C4-2-P). En el proyecto GEFE trabajamos en base al caso científico del proyecto ESTALLIDOS 6.0. Los estallidos de formación estelar (Starbursts o SB) son
Casiana
Muñoz Tuñón