Nahiely Flores–Fajardo*, Christophe Morisset**, and Luc Binette
Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264 04510, México D.F., México. (* nahiely@astroscu.unam.mx,** morisset@astroscu.unam.mx).
Received 2009 June 17
Accepted 2009 August 15
RESUMEN
]]> Los estudios del Gas Ionizado Difuso (DIG), hasta el momento se han hecho sin un consenso del criterio estricto para diferenciar entre el DIG y las regiones H II. En este trabajo recopilamos las mediciones de las líneas en emisión de 29 galaxias disponibles en la literatura, creando la primera base de datos del DIG (DIGEDA). Haciendo uso de esta base, analizamos las propiedades globales del DIG a partir de los cocientes de líneas [NII]λ6583/Hα, [O I]λ6300/Hα, [O III]λ5007/Hβ y [S II]λ6716/Hα, así como la medida de emisión de Hα. Este análisis nos permitió concluir que el cociente [NII]/Hα es un criterio general para diferenciar si una región en emisión es DIG o región HII, mientras que la EM(Hα) es una cantidad útil únicamente cuando consideramos galaxias por separado. Finalmente, encontramos que las regiones clasificadas como DIG en galaxias Irr parecen tener un comportamiento más cercano al de las regiones H II que al DIG en galaxias espirales.
ABSTRACT
Studies of the Diffuse Ionized Gas (DIG) have progressed without providing so far any strict criterion to distinguish DIGs from HII regions. In this work, we compile the emission line measurements of 29 galaxies that are available in the scientific literature, thereby setting up the first DIG database (DIGEDA). Making use of this database, we proceed to analyze the global properties of the DIG using the [NII]λ6583/Hα, [OI]λ6300/Hα, [O III]λ5007/Hβ and [S II]λ6716/Hα lines ratios, including the Hα emission measure. This analysis leads us to conclude that the [NII]/Hα ratio provides an objective criterion for distinguishing whether an emission region is a DIG or an HII region, while the EM(Hα) is a useful quantity only when the galaxies are considered individually. Finally, we find that the emission regions of Irr galaxies classified as DIG in the literature appear in fact to be much more similar to H II regions than to the DIGs of spiral galaxies.
Key Words: astronomical data bases: miscellaneous — galaxies: general — ISM: HII regions — ISM: lines and bands — line: formation.
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