The evolution of Radio Loud Quasar host galaxies: AO observations at z = 3

Abstract

We report on ESO--VLT adaptive optics imaging of one radio-loud quasar at z $\sim$ 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 M$_K$ $\sim$ --27 and effective radius R$_e$ = 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 $\sim$ 3 there is a deviation from a luminosity--redshift dependence regulated only by passive evolution.