The mean ultraviolet spectrum of a representative sample of faint z ∼ 3 Lyman alpha emitters
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 O III]λλ1661, 1666 Å 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 2018
- DOI:
- 10.1093/mnras/sty750
- arXiv:
- arXiv:1801.03085
- Bibcode:
- 2018MNRAS.477.2098N
- Keywords:
-
- galaxies: evolution;
- galaxies: high-redshift;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 15 pages, 9 figures. Accepted for publication in MNRAS