Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies

Akio K. Inoue*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

186 Citations (Scopus)


Finding the first generation of galaxies in the early Universe is the greatest step forward towards understanding galaxy formation and evolution. For a strategic survey of such galaxies and the interpretation of the obtained data, this paper presents an ultraviolet-to-optical spectral model of galaxies with a great care of the nebular emission. In particular, we present a machine-readable table of intensities of 119 nebular emission lines from Lyα to the rest-frame 1m as a function of metallicity from zero to the solar one. Based on the spectral model, we present criteria of equivalent widths of Lyα, Heiiλ1640, Hα, Hβ and [Oiii]λ5007 to select extremely metal-poor and metal-free galaxies although these criteria have uncertainty caused by the Lyman continuum escape fraction and the star formation duration. We also present criteria of broad-band colours which will be useful to select candidates for spectroscopic follow-up from drop-out galaxies. We propose the line intensity ratio of [Oiii]λ5007 to Hβ <0.1 as the most robust criterion for <1/1000 of the solar metallicity. This ratio of a galaxy with a few Myr-1 at z∼ 8 is detectable by spectroscopy with the James Webb Space Telescope within a reasonable exposure time.

Original languageEnglish
Pages (from-to)2920-2931
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 2011 Aug
Externally publishedYes


  • Cosmology: observations
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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