A Multiply-Imaged z ∼ 6.3 Lyman ɑ Emitter candidate behind Abell 2261

Creators: Rydberg, Claes-Erik; Zitrin, Adi; Zackrisson, Erik; Melinder, Jens; Whalen, Daniel J.; Klessen, Ralf S.; Gonzalez, Juan; Östlin, Göran; Carollo, Daniela

Abstract

While the Lyman α (Ly α) emission line serves as an important tool in the study of galaxies at z ≲ 6, finding Ly α emitters (LAE) at significantly higher redshifts has been more challenging, probably because of the increasing neutrality of the intergalactic medium above z ∼ 6. Galaxies with extremely high rest-frame Ly α equivalent widths, EW(Ly α) ≳ 150 Å, at z > 6, are good candidates for Ly α follow-up observations, and can stand out in multiband imaging surveys because of their unusual colours. We have conducted a photometric search for such objects in the Cluster Lensing And Supernova survey with Hubble (CLASH), and report here the identification of three likely gravitationally lensed images of a single LAE candidate at z ∼ 6.3, behind the galaxy cluster Abell 2261 (z = 0.225). In the process, we also measured with Keck/Multi-Object Spectrometer For Infra-Red Exploration the first spectroscopic redshift of a multiply imaged galaxy behind Abell 2261, at z = 3.337. This allows us to calibrate the lensing model, which, in turn, is used to study the properties of the candidate LAE. Population III galaxy spectral energy distribution model fits to the CLASH broad-band photometry of the possible LAE provide a slightly better fit than Population I/II models. The best-fitting model suggests intrinsic EW(Ly α) ≈160 Å after absorption in the interstellar and intergalactic medium. Future spectroscopic observations will examine this prediction as well as shed more light on the morphology of this object, which indicates that it may be a merger of two smaller galaxies.

Additional Information

© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 January 17. Received 2016 December 19; in original form 2016 October 21. CER acknowledges funding from the Swedish National Space Board and the Royal Swedish Academy of Sciences. CER, RSK and DJW were supported by the European Research Council under the European Community's Seventh Framework Programme (FP7/2007 – 2013) via the ERC Advanced Grant 'STARLIGHT: Formation of the First Stars' (project number 339177). EZ acknowledges financial support from the Swedish National Space Board, the Swedish Research Council (project 2011-5349) and the Wenner-Gren Foundation. RSK is further grateful for funding from the Deutsche Forschungsgemeinschaft DFG via SFB 881, 'The Milky Way System' (sub-projects B1, B2 and B8) and from SPP 1573 'Physics of the Interstellar Medium' (projects KL 1358/18.1, KL 1358/19.2). Support for AZ was provided by NASA through Hubble Fellowship grant #HST-HF2-51334.001-A awarded by STScI. The Keck observations were conducted by AZ together with Richard Ellis and Sirio Belli, and we thank their respective role. JG acknowledges financial support from the Wenner-Gren Foundation. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. AZ wishes to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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