Multicolour imaging of z = 2 QSO hosts

We present multicolour images of the hosts of three z = 2 QSOs previously detected in the R band by our group. The luminosities, colours and sizes of the hosts overlap with those of actively star-forming galaxies in the nearby Universe. Surface brightness radial profiles over the outer resolved areas roughly follow eithter an r(1/4) or an exponential law. These properties give support to the young host galaxy interpretation of the extended light around QSOs at high redshift, The rest-frame UV and UV-optical colours are inconsistent with the hypothesis of a scattered halo of light from the active nucleus by a simple optically thin scattering process produced by dust or hot electrons. If the UV light is indeed stellar, star formation rates of hundreds of solar masses per year are implied, an order of magnitude larger than in field galaxies at similar redshifts and above. This might indicate that the QSO phenomenon (at least the high-luminosity one) is preferentially accompanied by enhanced galactic activity at high redshifts.