The evolution of radio loud quasar host galaxies: AO observations at z ∼ 3

We report on ESO VLT adaptive optics imaging of one radio-loud quasar at z ∼ 3. In spite of the large distance of the object we are able to detect its surrounding extended nebulosity the properties of which are consistent with an underlying massive galaxy of MK ∼ −27 and effective radius Re = 7 kpc. As far as we know this is the clearest detection of a radio loud quasar host at high redshift. The host luminosity is indicative of the existence of massive spheroids even at this early cosmic epoch. The host luminosity is about 1 magnitude fainter than the expected value based on the average trend of the host galaxies of RLQ at lower redshift. The result, which however is based on a single object, suggests that at z ∼ 3 there is a deviation from a luminosity–redshift dependence regulated only by passive evolution.