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 galaxies and eight quasars, with z > 1.5. The survey, which is 80 per cent complete to K < 19.2 mag and complemented by R-band imaging, aimed at investigating whether extremely red objects are present in excess around high-z AGN, and to study the environment of z > 1.5 radio galaxies and radio-loud quasars. At 18 < K < 19 mag, the differential galaxy counts in our fields suggest 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 field. Consistently, we also find that the R - K colour distribution of all the galaxies in the AGN fields is significantly redder than the;colour distribution of the field galaxies. On the other hand, the distribution of the R - K colours is indistinguishable from that of galaxies taken from literature fields around radio-loud quasars at 1 < z < 2. We discuss the main implications of our findings and we compare the possible scenarios that could explain our results.