@article{040d45cf77284cca9cd5d835af18da42,
title = "A Spectroscopic Search for AGN Activity in the Reionization Era",
abstract = "The ubiquity of Lyman alpha (Lyα) emission in a sample of four bright [O iii]-strong star-forming galaxies with redshifts above seven has led to the suggestion that such luminous sources represent a distinct population compared with their fainter, more numerous counterparts. The presence of Lyα emission within the reionization era could indicate that these sources created early ionized bubbles due to their unusually strong radiation, possibly because of the presence of active galactic nuclei. To test this hypothesis, we secured long integration spectra with XSHOOTER on the VLT for three sources selected to have similar luminosities and prominent excess fluxes in the IRAC 3.6 or 4.5 μm band, usually attributed to strong [O iii] emission. We secured additional spectroscopy for one of these galaxies at z = 7.15 using MOSFIRE at the Keck telescope. For the most well-studied source in our sample with the strongest IRAC excess, we detect significant nebular emission from He ii and N v indicative of a non-thermal source. For the other two sources at z = 6.81 and z = 6.85, for which no previous optical/near-infrared spectroscopy was available, Lyα is seen in one and C iii] emission in the other. Although based on a modest sample, our results further support the hypothesis that the phenomenon of intense [O iii] emission is associated preferentially with sources lying in early ionized bubbles. However, even though one of our sources at z = 7.15 suggests the presence of non-thermal radiation, such ionized bubbles may not uniquely arise in this manner. We discuss the unique advantages of extending such challenging diagnostic studies with JWST.",
keywords = "early universe, galaxies: distances and redshifts, galaxies: evolution, galaxies: formation, infrared: galaxies, stars: formation",
author = "Nicolas Laporte and Kimihiko Nakajima and Ellis, {Richard S.} and Adi Zitrin and Stark, {Daniel P.} and Ramesh Mainali and Roberts-Borsani, {G. W.}",
note = "Funding Information: We acknowledge financial support from European Research Council Advanced Grant FP7/669253 (NL, RSE). D.P.S. acknowledges support from the National Science Foundation through grant AST-1410155. Funding Information: We thank an anonymous referee for very helpful comments on the paper. We acknowledge financial support from European Research Council Advanced Grant FP7/669253 (NL, RSE). D.P.S. acknowledges support from the National Science Foundation through grant AST-1410155. It is a pleasure to thank Rychard Bouwens, Masami Ouchi, Roser Pell{\'o}, and Daniel Schaerer for useful discussions. This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. The CANDELS program also includes observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The work is based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programmes ID 179. A-2005 and 097.A-0043 and data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. Further data was taken with the W.M. Keck Observatory on Mauna Kea, Hawaii, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. This Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish 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. Publisher Copyright: {\textcopyright} 2017. The American Astronomical Society. All rights reserved.",
year = "2017",
month = dec,
day = "10",
doi = "10.3847/1538-4357/aa96a8",
language = "English (US)",
volume = "851",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1",
}