The host galaxies of radio-quiet quasars at z ^*,**

¹ Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland e-mail: [totahy;jarkot]@utu.fi;orndahl@gmail.com
² INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy e-mail: falomo@pd.astro.it
³ INAF - IASF Milano, Via E. Bassini 15, 20133 Milano, Italy e-mail: uslenghi@mi.iasf.cnr.it

Received: 13 April 2006
Accepted: 27 September 2006

Abstract

We present near-infrared H-band imaging of 15 intermediate redshift () radio quiet quasars (RQQ) to characterize the properties of their host galaxies. We are able to clearly detect the surrounding nebulosity in 12 objects, whereas the object remains unresolved in three cases. For all the resolved objects, we find that the host galaxy is well represented by a de Vaucouleurs surface brightness law. This is the first reasonably sized sample of intermediate redshift RQQs studied in the near-infrared.
The RQQ host galaxies are luminous (average ) and large giant elliptical galaxies (average bulge scale length  kpc). RQQ hosts are ~1 mag brighter than the typical low redshift galaxy luminosity L^*, and their sizes are similar to those of galaxies hosting lower redshift RQQs, indicating that there is no significant evolution at least up to of the host galaxy structure. We also find that RQQ hosts are ~0.5-1 mag fainter than radio-loud quasar (RLQ) hosts at the similar redshift range. The comparison of the host luminosity of intermediate redshift RQQ hosts with that for lower z sources shows a trend that is consistent with that expected from the passive evolution of the stars in the host galaxies. The nuclear luminosity and the nucleus/host galaxy luminosity ratio of the objects in our sample are intermediate between those of lower redshift RQQs and those of higher redshift () RQQs.