{Excesses of faint galaxies around seven radio QSOs at 1.0

. We have conducted an optical study of the environments of seven radio-loud quasars at redshifts 1 < z < 1 . 6. In this paper we describe deep B and R band images obtained for fields of ∼ 6 × 6 arcmin around these quasars with 3 σ limiting magnitudes of B ∼ 26 and R ∼ 25 . 4. We found an statistically significant excess of faint ( B > 22 . 5 and R > 22 . 0) galaxies on scales of r < 170” and r < 35” around the quasars. The number of excess galaxies, their magnitudes and the angular extension of the excesses are compatible with clusters of galaxies at the redshift of the QSOs. We also found that the quasars of our sample are in general not located at the peak of the density distribution, lying in a projected distance of about ∼ 70” from it. This result agrees with the scenario of a link between overdensities of galaxies around radio sources and the origin of their radio emission.