LOFAR properties of SILVERRUSH Ly$\alpha$ emitter candidates in the ELAIS-N1 field

Abstract

Lyman alpha emitters (LAEs) in the Epoch of Reionization (EoR) offer valuable probes of early galaxy evolution and the process of reionization; however, the exact evolution of their abundance and the nature of their emission remain open questions. We combine samples of 229 and 349 LAE candidates at $z=5.7$ and $z=6.6,$ respectively, from the SILVERRUSH narrowband survey with deep Low Frequency Array (LOFAR) radio continuum observations in the ELAIS-N1 field to search for radio galaxies in the EoR and study the low-frequency radio properties of $z\gtrsim 5.7$ LAE emitters. Our LOFAR observations reach an unprecedented noise level of $\sim 20\mu$Jy beam${}^{-1}$ at 150MHz, and we detect five candidate LAEs at $>5\sigma$ significance. Based on detailed spectral energy distribution modelling of independent multi-wavelength observations, we conclude that these sources are likely [OII] emitters at $z=1.47$, yielding no reliable $z\gtrsim 5.7$ radio galaxy candidates. We examine the 111 $z=5.7$ and $z=6.6$ LAE candidates from our panchromatic photometry catalogue that are undetected by LOFAR, finding contamination rates of 81-92% for the $z=5.7$ and $z=6.6$ subset of the LAE candidate samples. This subset is biased towards brighter magnitudes and redder near-infrared colours. The contamination rates of the full sample will therefore likely be lower than the reported values. Contamination is lowered significantly through constraints on the near-infrared colours, highlighting the need for infrared observations to robustly identify bright LAEs in narrowband surveys. Finally, the stacking of radio continuum observations for the robust LAE samples yields 2$\sigma$ upper limits on radio luminosity of 8.2$\times$10${}^{23}$ and 8.7$\times$10${}^{23}$ W Hz${}^{-1}$ at $z=5.7$ and $6.6$, respectively, corresponding to limits on their median star-formation rates of $<$53 and $<$56 M${}_{\odot }$ yr${}^{-1}$.

arXiv comment17 pages, 11 figures, accepted for publication in A&A. The abstract is abridged. This paper is part of the 1st data release of the LoTSS Deep Fields

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