5 Conclusions

Adaptive-optics imaging in the H and K bands has been used to study the morphology of QSO host-galaxies at low and intermediate redshifts (z < 0.6). We detect the host-galaxies in 11 out of 12 quasars, of which 5 are radio-quiet and 7 are radio-loud. The images, obtained under poor seeing conditions, and with the QSOs themselves as reference for the correction, have typical spatial resolution of FWHM $\sim$ 0.3 arcsec before deconvolution. In the best case, the deconvolved H-band image of PG 1700+514 (with a spatial resolution of 0.16 arcsec) reveals a wealth of detail on the companion and the host-galaxy, and is probably the best-quality image of this object thus far.

Four of the quasars in our sample have close companions and show obvious signs of interactions. The two-dimensional images of three of the host-galaxies unambiguously reveal bars and spiral arms. For the other objects, it is difficult to determine the host-galaxy morphology on the basis of one dimensional surface brightness fits alone.

We have simulated mocked images of host-galaxies, both spirals and ellipticals, and applied the same analysis as to the data. Disk hosts can be missed for small disk scalelengths and large QSO contributions. In this case, the host-galaxy can be misidentified as an elliptical galaxy. Elliptical galaxies are always recognized as such, but with a luminosity which can be overestimated by up to 0.5 mag. The reason for this is that the method used here tends to attribute some of the QSO light to the host. This is also the case for disk galaxies with a strong contribution of the unresolved component.

Acknowledgements

We acknowledge the suggestions by the referee, Alan Stockton, that helped to improve the presentation. I. Márquez acknowledges financial support from the Spanish Ministerio de Educación y Ciencia (EX94-8826734). This work is financed by DGICyT grants PB93-0139 and PB96-0921. Financial support to develop the present investigation has been obtained through the Junta de Andalucía TIC-114.