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Spectroscopic properties of luminous Ly alpha emitters at z approximate to 6-7 and comparison to the Lyman-break population

J. Matthee, D. Sobral, B. Darvish, S. Santos, B. Mobasher, A. Paulino-Afonso, H. Rottgering, L. Alegre

Abstract
We present spectroscopic follow-up of candidate luminous Ly alpha emitters (LAEs) at z = 5.7-6.6 in the SA22 field with VLT/X-SHOOTER. We confirm two new luminous LAEs at z = 5.676 (SR6) and z = 6.532 (VR7), and also present HST follow-up of both sources. These sources have luminosities L-Ly (alpha) approximate to 3 x 10(43) erg s(-1), very high rest-frame equivalent widths of EW0 greater than or similar to 200 angstrom and narrow Ly a lines (200-340 km s-1). VR7 is the most UV-luminous LAE at z > 6.5, with M-1500 = -22.5, even brighter in the UV than CR7. Besides Ly alpha, we do not detect any other rest-frame UV lines in the spectra of SR6 and VR7, and argue that rest-frame UV lines are easier to observe in bright galaxies with low Ly a equivalent widths. We confirm that Ly alpha line widths increase with Ly alpha luminosity at z = 5.7, while there are indications that Ly alpha lines of faint LAEs become broader at z = 6.6, potentially due to reionization. We find a large spread of up to 3 dex in UV luminosity for > L-star LAEs, but find that the Ly alpha luminosity of the brightest LAEs is strongly related to UV luminosity at z = 6.6. Under basic assumptions, we find that several LAEs at z approximate to 6-7 have Ly alpha escape fractions greater than or similar to 100 per cent, indicating bursty star formation histories, alternative Ly alpha production mechanisms, or dust attenuating Ly alpha emission differently than UV emission. Finally, we present a method to compute xi(ion), the production efficiency of ionizing photons, and find that LAEs at z approximate to 6-7 have high values of log(10)(xi(ion)/Hz erg(-1)) approximate to 25.51 +/- 0.09 that may alleviate the need for high Lyman-Continuum escape fractions required for reionization.

Keywords
galaxies: evolution, galaxies: high-redshift, dark ages, reionization, first stars, cosmology: observations

Monthly Notices of the Royal Astronomical Society
Volume 472, Issue 1, Page 772
2017 August

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Fundação para a Ciência e a Tecnologia
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