Open AccessThe [O ii ]λ3727/Hα ratio of emission‐line galaxies in the 2dF Galaxy Redshift Survey
Author(s) -
Mouhcine M.,
Lewis I.,
Jones B.,
Lamareille F.,
Maddox S. J.,
Contini T.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.09211.x
Subject(s) - physics , astrophysics , galaxy , field galaxy , galaxy group , lenticular galaxy , redshift , metallicity , astronomy , redshift survey , brightest cluster galaxy , surface brightness fluctuation , luminosity , luminous infrared galaxy
We investigate the systematic variation of the [O ii ]λ3727/Hα flux line ratio as a function of various galaxy properties, i.e. luminosity, metallicity, reddening and excitation state, for a sample of 1124 emission‐line galaxies, with a mean redshift z ∼ 0.06 , drawn from the 2dF Galaxy Redshift Survey. The mean observed and extinction‐corrected emission‐line flux ratios agree well with the values derived from the B ‐band selected Nearby Field Galaxy Survey galaxy sample, but are significantly different from the values obtained from the Hα‐selected Universidad Complutense de Madrid Survey galaxy sample. This is because the different selection criteria applied in these surveys lead to a significant difference in the mean extinction and metallicity of different samples. We use the R 23 parameter to estimate the gas‐phase oxygen abundance and find that the extinction‐corrected [O ii ]λ3727/Hα ratio depends on the oxygen abundance. For 12 + log(O/H) ≳ 8.4 , we confirm that the emission‐line ratio decreases with increasing metallicity. We have extended the relationship further to the metal‐poor regime, 12 + log(O/H) ≲ 8.4 , and find that the correlation between the extinction‐corrected [O ii ]λ3727/Hα ratio and the metallicity reverses in comparison to the relationship for metal‐rich galaxies. For metal‐poor galaxies, in contrast with metal‐rich galaxies, the variation of extinction‐corrected [O ii ]λ3727/Hα ratio is correlated with the ionization states of the interstellar gas. The relative importance of the metallicity or the excitation state in determining the extinction‐corrected [O ii ]λ3727/Hα ratio depends on galaxy luminosity.