SC4K catalogue of candidate LAEs

The data reveal an extra power-law (or Schechter) component above L_Ly{alpha}_~=10^43.3^erg/s at z~2.2-3.5 and we show that it is partially driven by X-ray and radio active galactic nucleus (AGN), as their Ly{alpha} LF resembles the excess. The power-law component vanishes and/or is below our detection limits above z>3.5, likely linked with the evolution of the AGN population. The Ly {alpha} luminosity density rises by a factor ~2 from z~2 to 3 but is then found to be roughly constant (1.1^+0.2^_-0.2_x10^40^erg/s/Mpc^3^) to z~6, despite the ~0.7 dex drop in ultraviolet (UV) luminosity density.

The Ly{alpha}/UV luminosity density ratio rises from 4+/-1 per cent to 30+/-6 per cent from z~2.2 to 6. Our results imply a rise of a factor of ~=2 in the global ionization efficiency ({xi}_ion_) and a factor ~=4+/-1 in the Ly{alpha} escape fraction from z~2 to 6, hinting for evolution in both the typical burstiness/stellar populations and even more so in the typical interstellar medium conditions allowing Ly{alpha} photons to escape.