A HARD IONIZING SPECTRUM in z = 3-4 Lyα EMITTERS with INTENSE [O III ]EMISSION: ANALOGS of GALAXIES in the REIONIZATION ERA?

Kimihiko Nakajima, Richard S. Ellis, Ikuru Iwata, Akio K. Inoue, Haruka Kusakabe, Masami Ouchi, Brant E. Robertson

研究成果: Article査読

63 被引用数 (Scopus)

抄録

We present Keck/MOSFIRE spectra of the diagnostic nebular emission lines [O iii], [O ii], and Hβ for a sample of 15 redshift Lyα emitters (LAEs) and Lyman break galaxies (LBGs). In conjunction with spectra from other surveys, we confirm earlier indications that LAEs have a much higher [O iii]/[O ii] line ratio than is seen in similar redshift LBGs. By comparing their distributions on a [O iii]/[O ii] versus R23 diagram, we demonstrate that this difference cannot arise solely because of their lower metallicities but most likely is due to a harder ionizing spectrum. Using measures of Hβ and recombination theory, we demonstrate, for a subset of our LAEs, that - the number of Lyman continuum photons per UV luminosity - is indeed 0.2-0.5 dex larger than for typical LBGs at similar redshifts. Using photoionization models, we estimate the effect this would have on both [O iii]/[O ii] and R23 and conclude such a hard spectrum can only partially explain such intense line emission. The additional possibility is that such a large [O iii]/[O ii] ratio is in part due to density rather than ionization bound nebular regions, which would imply a high escape fraction of ionizing photons. We discuss how further observations could confirm this possibility. Clearly LAEs with intense [O iii] emission represent a promising analog of those sources with similarly strong lines that are thought to be an important contributor to cosmic reionization.

本文言語English
論文番号L9
ジャーナルAstrophysical Journal Letters
831
1
DOI
出版ステータスPublished - 2016 11 1
外部発表はい

ASJC Scopus subject areas

  • 天文学と天体物理学
  • 宇宙惑星科学

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