  Three high-redshift (z=2) and high luminosity (M_B < -28 mag for Ho = 50,
qo=0.5) QSOs, two radio-quiet one radio-loud, were imaged in R, I and K bands.
The luminosities, colours and sizes of the hosts overlap with those of actively
star-forming galaxies in the local Universe. 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 is
preferentially accompanied by enhanced galactic activity at high-redshift.

Astrophysics