The evolution of rest-frame UV properties, Ly alpha EWs, and the SFR-stellar mass relation at z similar to 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 109.3 +- 0.6 M and star formation rates (SFR) of SFRSED = 4.4+10.5 −2.4 M yr−1 and SFRLy 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. MUV 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 A (3σ), implying a low number density of (7 +- 1) x 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+280 −70 A, w0 = 129+11−11 A) from z ∼ 6 to z ∼ 2 and below. However, w0 is anticorrelated with MUV and stellar mass. Our results imply that sources selected as LAEs have a high Ly α escape fraction (fesc,Ly α) irrespective of cosmic time, but fesc,Ly α is still higher for UV-fainter and lower mass LAEs. The least massive LAEs (<109.5 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. Show more