The evolution of rest-frame UV properties, Ly α EWs, and the SFR–stellar mass relation at z ∼ 2–6 for SC4K LAEs

We explore deep rest-frame UV to FIR data in the COSMOS field to measure the individual spectral energy distributions (SED) of the ∼4000 SC4K (Sobral et al.) Lyman α (Ly α) emitters (LAEs) at z ∼ 2–6. We find typical stellar masses of 10^9.3 ± ^0.6 M☉ and star formation rates (SFR) of SFR_SED = 4.4⁺₋¹⁰_2.4⁵ M☉ yr⁻¹ and SFR_{Ly α} = 5.9⁺₋⁶₂³₆ M☉ yr⁻¹, combined with very blue UV slopes of β = −2.1⁺₋⁰₀⁵₄, but with significant variations within the population. M_UV and β are correlated in a similar way to UV-selected sources, but LAEs are consistently bluer. This suggests that LAEs are the youngest and/or most dust-poor subset of the UV-selected population. We also study the Ly α rest-frame equivalent width (EW₀) and find 45 ‘extreme’ LAEs with EW₀ > 240 Å (3σ), implying a low number density of (7 ± 1) × 10⁻⁷ Mpc⁻³. Overall, we measure little to no evolution of the Ly α EW₀ and scale length parameter (w₀), which are consistently high (EW₀ = 140⁺₋²⁸⁰₇₀ Å, w₀ = 129⁺₋¹¹₁₁ Å) from z ∼ 6 to z ∼ 2 and below. However, w₀ is anticorrelated with M_UV and stellar mass. Our results imply that sources selected as LAEs have a high Ly α escape fraction (f_{esc,Ly α}) irrespective of cosmic time, but f_{esc,Ly α} is still higher for UV-fainter and lower mass LAEs. The least massive LAEs (<10^9.5 M☉) are typically located above the star formation ‘main sequence’ (MS), but the offset from the MS decreases towards z ∼ 6 and towards 10¹⁰ M☉. Our results imply a lack of evolution in the properties of LAEs across time and reveals the increasing overlap in properties of LAEs and UV-continuum selected galaxies as typical star-forming galaxies at high redshift effectively become LAEs.