Collimation of extragalactic jets: evidence from hotspots

A linear relation with slope near unity is found between the logarithms of the hotspot size psi_HS perpendicular to the source major axis and the distance theta from the core for 14 compact &/or intense hotspots selected from a sample of 31 quasars having the largest angular sizes at various redshifts, as observed at 4.87 GHz with subarcsec resolution. A slope significantly less than 1 implies that the jet feeding the hotspot is laterally confined by the intergalactis medium, whereas a slope of 1 does not distinguish between a laterally confined jet and a free jet. Our relation has a slope near 1 and implies a 0.1 degree jet confined within a cone half-angle 15 to 20 degrees or a 1 degree wide free jet.