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The prevalence of galaxy overdensities around UV-luminous Lyman α emitters in the Epoch of Reionization

Leonova, E, Oesch, PA, Qin, Y, Naidu, RP, Wyithe, JSB, De Barros, S, Bouwens, RJ, Ellis, RS, Endsley, RM, Hutter, A, Illingworth, GD, Kerutt, J, Labbé, I, Laporte, N, Magee, D, Mutch, SJ, Roberts-Borsani, GW, Smit, R, Stark, DP, Stefanon, M , Tacchella, S and Zitrin, A (2022) The prevalence of galaxy overdensities around UV-luminous Lyman α emitters in the Epoch of Reionization. Monthly Notices of the Royal Astronomical Society, 515 (4). pp. 5790-5801. ISSN 0035-8711

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Before the end of the Epoch of Reionization, the Hydrogen in the Universe was predominantly neutral. This leads to a strong attenuation of Ly α lines of z ≳ 6 galaxies in the intergalactic medium. Nevertheless, Ly α has been detected up to very high redshifts (z ∼9) for several especially UV luminous galaxies. Here, we test to what extent the galaxy's local environment might impact the Ly α transmission of such sources. We present an analysis of dedicated Hubble Space Telescope (HST) imaging in the CANDELS/EGS field to search for fainter neighbours around three of the most UV luminous and most distant spectroscopically confirmed Ly α emitters: EGS-zs8-1, EGS-zs8-2, and EGSY-z8p7 at zspec = 7.73, 7.48, and 8.68, respectively. We combine the multiwavelength HST imaging with Spitzer data to reliably select z ∼7-9 galaxies around the central, UV-luminous sources. In all cases, we find a clear enhancement of neighbouring galaxies compared to the expected number in a blank field (by a factor ∼3-9×). Our analysis thus reveals ubiquitous overdensities around luminous Ly α emitting sources in the heart of the cosmic reionization epoch. We show that our results are in excellent agreement with expectations from the Dragons simulation, confirming the theoretical prediction that the first ionized bubbles preferentially formed in overdense regions. While three UV luminous galaxies already have spectroscopic redshifts, the majority of the remaining fainter, surrounding sources are yet to be confirmed via spectroscopy. JWST follow-up observations of the neighbouring galaxies identified here will thus be needed to confirm their physical association and to map out the ionized regions produced by these sources.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2022 Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press (OUP)
SWORD Depositor: A Symplectic
Date Deposited: 29 Nov 2022 10:36
Last Modified: 03 Feb 2023 09:43
DOI or ID number: 10.1093/mnras/stac1908
URI: https://researchonline.ljmu.ac.uk/id/eprint/18225
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