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Title:
Evidence for PopIII-like Stellar Populations in the Most Luminous Lyman-alpha Emitters at the Epoch of Reionization: Spectroscopic Confirmation
Authors:
Sobral, David; Matthee, Jorryt; Darvish, Behnam; Schaerer, Daniel; Mobasher, Bahram; Röttgering, Huub J. A.; Santos, Sérgio; Hemmati, Shoubaneh
Affiliation:
AA(Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, PT1349-018 Lisbon, Portugal; Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, Campo Grande, PT1749-016 Lisbon, Portugal; Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands;; 0000-0001-8823-4845), AB(Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands), AC(Department of Physics and Astronomy, University of California, 900 University Avenue, Riverside, CA 92521, USA), AD(Observatoire de Genève, Département d'Astronomie, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland; CNRS, IRAP, 14 Avenue E. Belin, F-31400 Toulouse, France), AE(Department of Physics and Astronomy, University of California, 900 University Avenue, Riverside, CA 92521, USA), AF(Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands), AG(Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, PT1349-018 Lisbon, Portugal; Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, Campo Grande, PT1749-016 Lisbon, Portugal;), AH(Department of Physics and Astronomy, University of California, 900 University Avenue, Riverside, CA 92521, USA 0000-0003-2226-5395)
Publication:
The Astrophysical Journal, Volume 808, Issue 2, article id. 139, 14 pp. (2015). (ApJ Homepage)
Publication Date:
08/2015
Origin:
IOP
Astronomy Keywords:
dark ages, reionization, first stars, early universe, galaxies: evolution
DOI:
10.1088/0004-637X/808/2/139
Bibliographic Code:
2015ApJ...808..139S

Abstract

Faint Lyalpha emitters become increasingly rarer toward the reionization epoch (z ˜ 6-7). However, observations from a very large (˜5 deg2) Lyalpha narrow-band survey at z = 6.6 show that this is not the case for the most luminous emitters, capable of ionizing their own local bubbles. Here we present follow-up observations of the two most luminous Lyalpha candidates in the COSMOS field: ``MASOSA'' and ``CR7.'' We used X-SHOOTER, SINFONI, and FORS2 on the Very Large Telescope, and DEIMOS on Keck, to confirm both candidates beyond any doubt. We find redshifts of z = 6.541 and z = 6.604 for ``MASOSA'' and ``CR7,'' respectively. MASOSA has a strong detection in Lyalpha with a line width of 386 ± 30 km s-1 (FWHM) and with very high EW0 (>200 Å), but undetected in the continuum, implying very low stellar mass and a likely young, metal-poor stellar population. ``CR7,'' with an observed Lyalpha luminosity of 1043.92±0.05 erg s-1 is the most luminous Lyalpha emitter ever found at z > 6 and is spatially extended (˜16 kpc). ``CR7'' reveals a narrow Lyalpha line with 266 ± 15 km s-1 FWHM, being detected in the near-infrared (NIR) (rest-frame UV; beta = -2.3 ± 0.1) and in IRAC/Spitzer. We detect a narrow He ii 1640 Å emission line (6sigma, FWHM = 130 ± 30 km s-1) in CR7 which can explain the clear excess seen in the J-band photometry (EW0 ˜ 80 Å). We find no other emission lines from the UV to the NIR in our X-SHOOTER spectra (He ii/O iii] 1663 Å > 3 and He ii/C iii] 1908 Å > 2.5). We conclude that CR7 is best explained by a combination of a PopIII-like population, which dominates the rest-frame UV and the nebular emission, and a more normal stellar population, which presumably dominates the mass. Hubble Space Telescope/WFC3 observations show that the light is indeed spatially separated between a very blue component, coincident with Lyalpha and He ii emission, and two red components (˜5 kpc away), which dominate the mass. Our findings are consistent with theoretical predictions of a PopIII wave, with PopIII star formation migrating away from the original sites of star formation.

Based on observations obtained with X-SHOOTER, FORS2, and SINFONI on the VLT, ESO DDT time (294.A-5018, 294.A-5039) and with DEIMOS on Keck II (U082D).

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