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

Abstract

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^{+10.5}_{-2.4} M_⊙ yr^-1 and SFR_{Ly α }=5.9^{+6.3}_{-2.6} M_⊙ yr^-1, combined with very blue UV slopes of β =-2.1^{+0.5}_{-0.4}, 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 EW<sub>0</sub> > 240 Å (3σ), implying a low number density of (7 ± 1) × 10<sup>-7</sup> Mpc<sup>-3</sup>. Overall, we measure little to no evolution of the Ly α EW<sub>0</sub> and scale length parameter (w<sub>0</sub>), which are consistently high (EW_0=140^{+280}_{-70} Å, w_0=129^{+11}_{-11} Å) from z ∼ 6 to z ∼ 2 and below. However, w<sub>0</sub> is anticorrelated with M<sub>UV</sub> and stellar mass. Our results imply that sources selected as LAEs have a high Ly α escape fraction (f<sub>esc,Ly α</sub>) irrespective of cosmic time, but f<sub>esc,Ly α</sub> is still higher for UV-fainter and lower mass LAEs. The least massive LAEs (<10<sup>9.5</sup> M<sub>⊙</sub>) 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.