An ALMA [CII] survey of the environments around bright Lyman-α emitters in the epoch of re-ionisation

Cooper, Ryan and Newton, Bentley and Fletcher, Matthew and Muller, Catherine and Turner, Kyle and Sobral, David (2020) An ALMA [CII] survey of the environments around bright Lyman-α emitters in the epoch of re-ionisation. Notices of Lancaster Astrophysics (NLUAstro), 2. pp. 53-70.

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Abstract

The bright early Lyman-α emitters (LAEs) studied here (CR7, VR7 and MASOSA) are some of the brightest known LAEs at high redshift. These galaxies likely reside in early ionised bubbles, producing a significant amount of ionising photons to sustain and reionise the surrounding intergalactic medium during the epoch of reionisation (EoR). It is not clear how those early ionised bubbles formed, but studying luminous LAEs in the EoR could bring us closer to understanding the processes involved. Here we use deep ALMA observations (σ ~ 5mJy/beam km/s) obtained around each bright distant LAE to survey for [CII] emitters at z≈6.5-7.1. This was done by looking for line emitters in the ALMA data using SExtractor and other statistical analysis methods. We have identified 9, 11 & 5 robust candidate [CII] line emitters within the full data-sets for CR7, VR7 & MASOSA respectively. By dividing the number density of sources in the vicinity of each LAE by the average number density of [CII] emitters at z≈7, we find that the immediate environment of bright LAEs is over-dense by factors of about 2 to 4. Our results are consistent with luminous LAEs within the epoch of re-ionisation being in moderately over-dense regions.