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Searching for Islands of Reionization: A Potential Ionized Bubble Powered by a Spectroscopic Overdensity at z = 8.7

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jats:titleAbstract</jats:title> jats:pWe present the results from a spectroscopic survey using the MOSFIRE near-infrared spectrograph on the 10 m Keck telescope to search for Lyjats:italicα</jats:italic> emission from candidate galaxies at jats:italicz</jats:italic> ∼ 9–10 in four of the CANDELS fields (GOODS-N, EGS, UDS, and COSMOS). We observed 11 target galaxies, detecting Lyjats:italicα</jats:italic> from one object in ∼8.1 hr of integration, at jats:italicz</jats:italic> = 8.665 ± 0.001 with an integrated signal-to-noise ratio > 7. This galaxy is in the CANDELS Extended Groth Strip (EGS) field and lies physically close (3.5 physical Mpc [pMpc]) to another confirmed galaxy in this field with Lyjats:italicα</jats:italic> detected at jats:italicz</jats:italic> = 8.683. The detection of Lyjats:italicα</jats:italic> suggests the existence of large (∼1 pMpc) ionized bubbles fairly early in the reionization process. We explore the ionizing output needed to create bubbles of this size at this epoch and find that such a bubble requires more than the ionizing power provided by the full expected population of galaxies (by integrating the UV luminosity function down to jats:italicM</jats:italic> jats:subUV</jats:sub> = −13). The Lyjats:italicα</jats:italic> we detect would be able to escape the predominantly neutral intergalactic medium at this epoch if our detected galaxy is inhabiting an overdensity, which would be consistent with the photometric overdensity previously identified in this region by Finkelstein et al. This implies that the CANDELS EGS field is hosting an overdensity at jats:italicz</jats:italic> = 8.7 that is powering one or more ionized bubbles, a hypothesis that will be imminently testable with forthcoming James Webb Space Telescope observations in this field.</jats:p>



5109 Space Sciences, 51 Physical Sciences, 5101 Astronomical Sciences

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American Astronomical Society