Evidence that nearby bright galaxies contain massive dark objects in their center has become increasingly compelling over the last few years and early suggestions that a tight correlation exists between the mass of the dark object and the mass of the bulge (Kormendy & Richstone 1995) have been convincingly corroborated (Magorrian et al. 1998; Ferrarese & Merrit 2000). It is thus possible that AGN activity is a usual episode of the history of most, if not all, present-day bright galaxies. One way to investigate this is to determine the luminosity and morphology of galaxies hosting quasars. In addition, this gives clues on the range of conditions needed for strong nuclear activity to occur.
Recent observations of host-galaxies with HST have questioned the previous belief that radio-loud and radio-quiet quasars are found preferentially in the center of, respectively, elliptical and spiral galaxies (Bahcall et al. 1997; McLure et al. 1999). This supports previous conclusions from IR ground-based observations (Dunlop et al. 1993; McLeod & Rieke 1995; Taylor et al. 1996) that the distinction in host-galaxy characteristics between the two classes of QSOs is subtle (see also Hooper et al. 1997, for larger redshift). More surprising is the finding by McLure et al. (1999) that host-galaxies of luminous AGNs (both radio-quiet and radio-loud) are all massive ellipticals whereas Bahcall et al. (1997) found that, in the same redshift range, host-galaxies are of various morphologies but that all radio-loud quasars have bright elliptical hosts or occur in interacting systems (Kirkhakos et al. 1999).
The detection and analysis of host-galaxies is difficult even from space (Bahcall et al. 1994; Bahcall et al. 1995; McLeod & Rieke 1995; McLeod & McLeod 2001). Indeed, the determination of the PSF and the subtraction of the point source image are crucial in this work. Differentiation between the two classical profiles, either an exponential disk or a de Vaucouleurs power-law, is effective only in the regions close to the center, or in the far-wings of the PSF (see Fig. 1 of McLure et al. 2000). This is the main limiting factor in determining host-galaxy morphologies from the ground. With the advent of adaptive optics, it will be possible to alleviate the seeing limitation (Stockton et al. 1998; Aretxaga et al. 1998; Hutchings et al. 1999). Observing in the infrared minimizes the difference in luminosity between the host and nucleus again improving our ability to determine the host morphology.
PSF determination is still a major problem but the difficulties are balanced by the prospect of using very soon 10 m class telescopes which will provide higher sensitivity and better spatial resolution.
In this paper we present the result of a pilot programme aiming at testing the capabilities of adaptive optics in this field. We present the data in Sect. 2, discuss each object in Sect. 3, analyze the results in Sect. 4 and conclude in Sect. 5.
Copyright ESO 2001