The mean ultraviolet spectrum of a representative sample of faint z ~ 3 Lyman alpha emitters

Kimihiko Nakajima, Thomas Fletcher, Richard S. Ellis, Brant E Robertson, Ikuru Iwata

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

We discuss the rest-frame ultraviolet (UV) emission line spectra of a large (~100) sample of low luminosity redshift z ~ 3.1 Lyman alpha emitters (LAEs) drawn from a Subaru imaging survey in the SSA22 survey field. Our earlier work based on smaller samples indicated that such sources have high [O III]/[O II] line ratios possibly arising from a hard ionizing spectrum that may be typical of similar sources in the reionization era.With optical spectra secured from VLT/VIMOS, we re-examine the nature of the ionizing radiation in a larger sample using the strength of the high ionization diagnostic emission lines of CIII]λ1909, CIVλ1549, HeIIλ1640, and OIII]λλ1661, 1666Å in various stacked subsets. Our analysis confirms earlier suggestions of a correlation between the strength of Ly α and CIII] emission and we find similar trends with broad-band UV luminosity and rest-frame UV colour. Using various diagnostic line ratios and our stellar photoionization models, we determine both the gas phase metallicity and hardness of the ionization spectrum characterized by ξion - the number of Lyman continuum photons per UV luminosity. We confirm our earlier suggestion that ξion is significantly larger for LAEs than for continuum-selected Lyman break galaxies, particularly for those LAEs with the faintest UV luminosities.We briefly discuss the implications for cosmic reionization if the metal-poor intensely star-forming systems studied here are representative examples of those at much higher redshift.

Original languageEnglish (US)
Pages (from-to)2098-2111
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Volume477
Issue number2
DOIs
StatePublished - Jun 21 2018
Externally publishedYes

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ultraviolet spectra
emitters
luminosity
suggestion
ionization
continuums
ion
ultraviolet emission
ionizing radiation
field survey
set theory
hardness
metallicity
line spectra
photoionization
optical spectrum
ions
emission spectra
vapor phases
galaxies

Keywords

  • Galaxies: Evolution
  • Galaxies: High-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The mean ultraviolet spectrum of a representative sample of faint z ~ 3 Lyman alpha emitters. / Nakajima, Kimihiko; Fletcher, Thomas; Ellis, Richard S.; Robertson, Brant E; Iwata, Ikuru.

In: Monthly Notices of the Royal Astronomical Society, Vol. 477, No. 2, 21.06.2018, p. 2098-2111.

Research output: Contribution to journalArticle

Nakajima, Kimihiko ; Fletcher, Thomas ; Ellis, Richard S. ; Robertson, Brant E ; Iwata, Ikuru. / The mean ultraviolet spectrum of a representative sample of faint z ~ 3 Lyman alpha emitters. In: Monthly Notices of the Royal Astronomical Society. 2018 ; Vol. 477, No. 2. pp. 2098-2111.
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AB - We discuss the rest-frame ultraviolet (UV) emission line spectra of a large (~100) sample of low luminosity redshift z ~ 3.1 Lyman alpha emitters (LAEs) drawn from a Subaru imaging survey in the SSA22 survey field. Our earlier work based on smaller samples indicated that such sources have high [O III]/[O II] line ratios possibly arising from a hard ionizing spectrum that may be typical of similar sources in the reionization era.With optical spectra secured from VLT/VIMOS, we re-examine the nature of the ionizing radiation in a larger sample using the strength of the high ionization diagnostic emission lines of CIII]λ1909, CIVλ1549, HeIIλ1640, and OIII]λλ1661, 1666Å in various stacked subsets. Our analysis confirms earlier suggestions of a correlation between the strength of Ly α and CIII] emission and we find similar trends with broad-band UV luminosity and rest-frame UV colour. Using various diagnostic line ratios and our stellar photoionization models, we determine both the gas phase metallicity and hardness of the ionization spectrum characterized by ξion - the number of Lyman continuum photons per UV luminosity. We confirm our earlier suggestion that ξion is significantly larger for LAEs than for continuum-selected Lyman break galaxies, particularly for those LAEs with the faintest UV luminosities.We briefly discuss the implications for cosmic reionization if the metal-poor intensely star-forming systems studied here are representative examples of those at much higher redshift.

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