Multicolour imaging of z=2 QSO hosts

We present multicolour images of the hosts of three z=2 QSOs previously detected in 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 either a 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 acompanied by enhanced galactic activity at high-redshifts. (orig.)Available from TIB Hannover: RR 4697(1055) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Adaptive optics observations of LBQS 0108+0028: K-band detection of the host galaxy of a radio-quiet QSO at z #approx# 2

We report the first unambiguous detection of the host galaxy of a normal radio-quiet QSO at high-redshift in K-band. The luminosity of the host comprises about 35% of the total K-band luminosity. Assuming the average colour of QSOs at z#approx#2, the host would be about 5 to 6 mag brighter than an unevolved L_* galaxy placed at z#approx#2, and 3 to 4 mag brighter than a passively evolved L_* galaxy at the same redshift. The luminosity of the host galaxy of the QSO would thus overlap with the highest found in radio-loud QSOs and radio-galaxies at the same redshift. (orig.)Available from TIB Hannover: RR 4697(1093) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman