Volume 579, July 2015
|Number of page(s)||9|
|Published online||19 June 2015|
New candidates for extremely metal-poor emission-line galaxies in the SDSS/BOSS DR10⋆
1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 Main Astronomical Observatory, Ukrainian National Academy of Sciences, Zabolotnoho 27, 03680 Kyiv, Ukraine
3 Institut für Astrophysik, Göttingen Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
4 Astronomy Department, King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
Received: 20 January 2015
Accepted: 30 April 2015
We present a spectroscopic study of eight extremely low-metallicity candidate emission-line galaxies with oxygen abundances possibly below 12 + log O/H = 7.35. These galaxies were selected from data release 10 of the Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey (SDSS/BOSS DR10). We will call these extremely metal-deficient (XMD) galaxies. The electron temperature-sensitive emission line [O iii] λ4363 is detected in three galaxies and marginally detected in two galaxies, allowing for abundance determination by a “direct” method. Because of large uncertainties in the [O iii]λ4363 Å line fluxes, we also calculated oxygen abundance in these galaxies together with the remaining three galaxies using a strong-line semi-empirical method. This method gives oxygen abundances higher than 7.35 for three galaxies with detected [O iii]λ4363 Å line and lower than 7.35 for the remaining five objects of the sample. The newly-discovered galaxies represent excellent targets for follow-up spectroscopic observations with the largest telescopes to improve the oxygen abundance determination and to increase the number of these very rare low-metallicity objects. The extreme location of the most massive and luminous XMD galaxies and XMD candidates in the stellar mass–metallicity diagram implies that these galaxies may be genuine young objects. With stellar masses of up to ~107–108M⊙, the galaxies are not chemically enriched and strongly deviate to lower metallicity as compared to the relation obtained for a large sample of low-redshift, star-forming galaxies.
Key words: galaxies: abundances / galaxies: irregular / galaxies: evolution / galaxies: formation / galaxies: ISM / ISM: abundances
Tables 2–4 are available in electronic form at http://www.aanda.org
© ESO, 2015
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