Volume 474, Number 3, November II 2007
|Page(s)||807 - 814|
|Published online||23 October 2007|
Checking the reliability of equivalent width R23 for estimating the metallicities of galaxies
National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, PR China e-mail: firstname.lastname@example.org
2 GEPI, Observatoire de Paris-Meudon, 92195 Meudon, France
3 Department of Physics, Hebei Normal University, Shijiazhuang 050016, PR China
4 Department of Physics, Harbin University, Haerbin 150086, PR China
Accepted: 8 August 2007
Aims.We verify whether the O/H abundances of galaxies can be derived from the equivalent width (EW) R23 instead of the extinction-corrected flux R23, and eventually propose a method of improving the reliability of this empirical method, which is often used for the non-flux calibrated spectra of galaxies.
Methods.We select 37 173 star-forming galaxies from the Second Data Release of the Sloan Digital Sky Survey (SDSS-DR2), which offers a wide range of properties to test the EW method.
Results.The EW-R23 method brings with it a significant bias: for the bulk of SDSS galaxies, it may affect the determination of (O/H) by factors ranging from –0.2 to 0.1 dex and for some galaxies by factors ranging from –0.5 to 0.2 dex. We characterize this discrepancy (or bias) by )/(, which is virtually independent of dust extinction, while tightly correlating with Dn(4000), although at a lower significance, with () colors.
Conclusions.The EW-R23 method cannot be used as a proxy for the extinction-corrected flux R23 method. From analytical third-order polynomial fits of α versus () colors, we have been able to correct the EW-R23 method. With this additional and easy correction, the EW-R23 method provides O/H abundance values similar to those derived from the extinction-corrected flux R23 method with an accuracy of ±0.1 dex for >92% of the SDSS galaxies.
Key words: galaxies: abundances / galaxies: evolution / galaxies: ISM / galaxies: photometry / galaxies: spiral / galaxies: starburst
© ESO, 2007
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