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We investigate the prevalence of AGN in the high-redshift protocluster$\rm{Cl}\,0218.3$-$0510$ at $z=1.62$. Using imaging from the Chandra X-rayTelescope, we find a large overdensity of AGN in the protocluster; a factor of$23\pm9$ times the field density of AGN. Only half of this AGN overdensity isdue to the overdensity of massive galaxies in the protocluster (a factor of$11\pm2$), as we find that $17^{+6}_{-5}\%$ of massive galaxies ($M_* >10^{10}\,\rm{M}_{\odot}$) in the protocluster host an X-ray luminous AGN,compared to $8\pm1\%$ in the field. This corresponds to an enhancement of AGNactivity in massive protocluster galaxies by a factor of $2.1\pm0.7$ at$1.6\sigma$ significance. We also find that the AGN overdensity is centrallyconcentrated, located within 3 arcmin and most pronounced within 1 arcmin ofthe centre of the protocluster. Our results confirm that there is a reversal inthe local anti-correlation between galaxy density and AGN activity, so there isan enhancement of AGN in high-redshift protoclusters. We compare the propertiesof AGN in the protocluster to the field and find no significant differences inthe distributions of their stellar mass, X-ray luminosity, or hardness ratio.We therefore suggest that triggering mechanisms are similar in bothenvironments, and that the mechanisms simply occur more frequently in denserenvironments.

Enhancement of AGN in a protocluster at z=1.6