The X-ray and radio activity of typical and luminous Ly α emitters from z ∼ 2 to z ∼ 6: evidence for a diverse, evolving population

Despite recent progress in understanding Ly α emitters (LAEs), relatively little is known regarding their typical black hole activity across cosmic time. Here, we study the X-ray and radio properties of ∼4000 LAEs at 2.2 < z < 6 from the SC4K survey in the COSMOS field. We detect 254 (6.8{{ per cent}} ± 0.4{{ per cent}}) LAEs individually in the X-rays (S/N > 3) with an average luminosity of 10^{44.31± 0.01} erg s^{-1} and average black hole accretion rate (BHAR) of 0.72 ± 0.01 M_⊙ yr^-1, consistent with moderate to high accreting active galactic neuclei (AGNs). We detect 120 sources in deep radio data (radio AGN fraction of 3.2{{ per cent}} ± 0.3{{ per cent}}). The global AGN fraction (8.6{{ per cent}} ± 0.4{{ per cent}}) rises with Ly α luminosity and declines with increasing redshift. For X-ray-detected LAEs, Ly α luminosities correlate with the BHARs, suggesting that Ly α luminosity becomes a BHAR indicator. Most LAEs (93.1{{ per cent}} ± 0.6{{ per cent}}) at 2 < z < 6 have no detectable X-ray emission (BHARs < 0.017 M_⊙ yr^-1). The median star formation rate (SFR) of star-forming LAEs from Ly α and radio luminosities is 7.6^{+6.6}_{-2.8} M_⊙ yr^-1. The black hole to galaxy growth ratio (BHAR/SFR) for LAEs is <0.0022, consistent with typical star-forming galaxies and the local BHAR/SFR relation. We conclude that LAEs at 2 < z < 6 include two different populations: an AGN population, where Ly α luminosity traces BHAR, and another with low SFRs which remain undetected in even the deepest X-ray stacks but is detected in the radio stacks.