Sobral, David; Matthee, Jorryt JISTA ; Darvish, Behnam; Schaerer, Daniel; Mobasher, Bahram; Röttgering, Huub; Santos, Sérgio; Hemmati, Shoubaneh
Faint Lyα emitters become increasingly rarer toward the reionization epoch (z ∼ 6–7). However, observations from a very large (∼5 deg2) Lyα 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 Lyα 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 Lyα 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 Lyα luminosity of 1043.92±0.05 erg s−1 is the most luminous Lyα emitter ever found at z > 6 and is spatially extended (∼16 kpc). “CR7” reveals a narrow Lyα line with 266 ± 15 km s−1 FWHM, being detected in the near-infrared (NIR) (rest-frame UV; β = −2.3 ± 0.1) and in IRAC/Spitzer. We detect a narrow He II 1640 Å emission line (6σ, 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 Lyα 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.
The Astrophysical Journal
We thank the anonymous reviewer for useful and constructive comments and suggestions which greatly improved the quality and clarity of our work. D.S. acknowledges financial support from the Netherlands Organisation for Scientific research (NWO) through a Veni fellowship, from FCT through a FCT Investigator Starting Grant and Start-up Grant (IF/01154/2012/CP0189/CT0010), from FCT grant UID/FIS/04434/2013, and from LSF and LKBF. J.M. acknowledges the award of a Huygens PhD fellowship. H.R. acknowledges support from the ERC Advanced Investigator program NewClusters 321271. The authors thank Mark Dijkstra, Bhaskar Agarwal, Jarrett Johnson, Andrea Ferrara, Jarle Brinchmann, Rebecca Bowler, George Becker, Emma Curtis-Lake, Milos Milosavljevic, Raffaella Schneider, Paul Shapiro, and Erik Zackrisson for interesting, stimulating and helpful discussions. The authors are extremely grateful to ESO for the award of ESO DDT time (294.A-5018 and 294.A-5039) which allowed the spectroscopic confirmation of both sources and the detailed investigation of their nature. Observations are also based on data from W.M. Keck Observatory. The W.M. Keck Observatory is operated as a scientific partnership of Caltech, the University of California and the National Aeronautics and Space Administration. Based on observations obtained with MegaPrime/Megacam, a joint project of CFHT and CEA/IRFU, at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de lUnivers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at Terapix available at the Canadian Astronomy Data Centre as part of the Canada–France–Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programme IDs 294.A-5018, 294.A-5039, and 179.A-2005, and on data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. The authors acknowledge the award of service time (SW2014b20) on the William Herschel Telescope (WHT). WHT and its service programme are operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.
Sobral D, Matthee JJ, Darvish B, et al. Evidence for PopIII-like stellar populations in the most luminous Lyα emitters at the epoch of reionisation: Spectroscopic confirmation. The Astrophysical Journal. 2015;808(2):139. doi:10.1088/0004-637X/808/2/139
Sobral, D., Matthee, J. J., Darvish, B., Schaerer, D., Mobasher, B., Röttgering, H., … Hemmati, S. (2015). Evidence for PopIII-like stellar populations in the most luminous Lyα emitters at the epoch of reionisation: Spectroscopic confirmation. The Astrophysical Journal. IOP Publishing. https://doi.org/10.1088/0004-637X/808/2/139
Sobral, David, Jorryt J Matthee, Behnam Darvish, Daniel Schaerer, Bahram Mobasher, Huub Röttgering, Sérgio Santos, and Shoubaneh Hemmati. “Evidence for PopIII-like Stellar Populations in the Most Luminous Lyα Emitters at the Epoch of Reionisation: Spectroscopic Confirmation.” The Astrophysical Journal. IOP Publishing, 2015. https://doi.org/10.1088/0004-637X/808/2/139.
D. Sobral et al., “Evidence for PopIII-like stellar populations in the most luminous Lyα emitters at the epoch of reionisation: Spectroscopic confirmation,” The Astrophysical Journal, vol. 808, no. 2. IOP Publishing, p. 139, 2015.
Sobral D, Matthee JJ, Darvish B, Schaerer D, Mobasher B, Röttgering H, Santos S, Hemmati S. 2015. Evidence for PopIII-like stellar populations in the most luminous Lyα emitters at the epoch of reionisation: Spectroscopic confirmation. The Astrophysical Journal. 808(2), 139.
Sobral, David, et al. “Evidence for PopIII-like Stellar Populations in the Most Luminous Lyα Emitters at the Epoch of Reionisation: Spectroscopic Confirmation.” The Astrophysical Journal, vol. 808, no. 2, IOP Publishing, 2015, p. 139, doi:10.1088/0004-637X/808/2/139.