Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010acasn..51....8g&link_type=abstract
Acta Astronomica Sinica, vol. 51, no. 1, p. 8-17
Astronomy and Astrophysics
Astronomy
Galaxies: Abundances, Galaxies: Evolution, Galaxies: Fundamental Parameters, Galaxies: Ism
Scientific paper
Although the Hα emission line provides a useful star formation rate (SFR) indicator for nearby galaxies, it is not easily observed for distant galaxies since this line shifts out of the visible band for z>0.4. Instead, the [O II]λ3727 line is often used as an alternative indicator of SFR. Unfortunately, the [O II] emission line is subjected to several factors, such as reddening, excitation state and abundance dependence. To investigate the systematic dependence of the [O II]λ3727/Hα flux ratio on these different factors, 105 emission line galaxies are selected from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4). The effective V-band optical depths (TV) of galaxies are calculated based on fluxes of Hα and Hβ lines. The dust extinction correction is very important to the [O II]λ3727/Hαflux ratio. The mean observed and extinction-corrected flux ratios are 0.48 and 0.89, respectively. The extinction-corrected [O II]λ3727/Hα flux ratio correlates with the ionization states of the interstellar gas for metal-poor galaxies, but there is no strong dependence for metal-rich galaxies. In additional, the [O II]λ3727/Hα ratio depends on the oxygen abundance. For 12+lg(O/H)>8.5, the emission-line ratio decreases with the increase of metallicity and conversely for metal-poor galaxies. We provide simple formulae to estimate the [O II]λ3727/Hα flux ratio as a function of metallicity and excitation state. These formulae can be used to calculate SFR of galaxies with z>0.4, such as galaxies to be observed from the deep field survey of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST).
Gao Fei
Kong Xin-wei
Lin Ja-Ren
Lin Xiao-Biao
Zhang Wanchuan
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