The density of extremely red objects around high-z radio-loud active galactic nuclei

We present the results of a K-band imaging survey of 40 arcmin(2) in fields around 14 radio-loud active galactic nuclei (AGN), comprising six radio ga laxies and eight quasars, with z > 1.5. The survey, which is 80 per cent co mplete to K < 19.2 mag and complemented by R-band imaging, aimed at investi gating whether extremely red objects are present in excess around high-z AG N, and to study the environment of z > 1.5 radio galaxies and radio-loud qu asars. At 18 < K < 19 mag, the differential galaxy counts in our fields sug gest a systematic excess over the general field counts. At K < 19.2 mag we find an excess of galaxies with R - K > 6 in comparison with the general fi eld. Consistently, we also find that the R - K colour distribution of all t he galaxies in the AGN fields is significantly redder than the;colour distr ibution of the field galaxies. On the other hand, the distribution of the R - K colours is indistinguishable from that of galaxies taken from literatu re fields around radio-loud quasars at 1 < z < 2. We discuss the main impli cations of our findings and we compare the possible scenarios that could ex plain our results.