Fraction of X-ray selected AGNs in a sample of protoclusters as a function of redshift. The different symbol shapes and colors correspond to different structures and selection methods of the parent galaxy population, as marked in the figure. Different symbols for the same structure are slightly shifted in redshift for clarity. We consider the parent samples of spectroscopically confirmed protocluster members, when available (filled symbols); otherwise we consider all the member candidates (empty symbols). We refer to Sect. 4.2 and Appendix B for the computation of these values and the relevant citations. For comparison with low-redshift, virialised systems, the filled and hashed yellow stripes represent the X-ray AGN fractions in galaxy clusters presented by Martini et al. (2009) and Bufanda et al. (2017), respectively.