HIGH SPATIAL-RESOLUTION IMAGING OF 10-3CR GALAXIES WITH ZETA-GREATER-THAN-OR-EQUAL-TO-1 AND STATISTICAL EVIDENCE FOR SELECTION EFFECTS FROM GRAVITATIONAL AMPLIFICATION

We present here broad-band filter imaging of 10 3CR galaxies with z ≥ 1 and narrow-band filter imaging of three of these, with high spatial resolution (0″.6 ≤ FWHM ≤ 1″.2, mean FWHM = 0″.76). New data in favor of the gravitational lensing interpretation of 3C 324 are presented, and the existence of an extremely distant cluster of galaxies around 3CR 239 at z = 1.78 is suggested. So far we have observed 27 3CR galaxies with z ≥ 1 with an unprecedented mean image quality FWHM = 0″.74 (σ = 0″.15). It reveals the very unusual morphologies of these galaxies: f of them are resolved in two to six components over ∼ 50(H0/50) kpc at a flux level 4 σ above the sky noise, with sizes and luminosities of each component comparable to bright galaxies. We present statistical evidence of an excess of bright foreground galaxies on the lines of sight of the 3CR galaxies with z ≥ 1, in the sense that there is as much as 9 times more high-z 3CR galaxies around R ≤ 21 mag galaxies than would be expected from a random distribution. An excess of foreground distant clusters of galaxies is also found at a lower statistical level. A case-by-case analysis shows that the foreground bright galaxies, and one of the foreground clusters, actually gravitationally amplify the background 3CR galaxies by 0.5-2 mag. Finally, we investigate how the contamination by foreground fainter galaxies, and the gravitational amplification/lensing effects they can induce, could affect the observed properties of the high-z 3CR galaxies, and hence their current interpretations.