1 Introduction

Attempts to understand properties of active galactic nuclei (AGN) and their cosmological evolution has led to the conclusion that the AGN activity as a whole is most likely to be described as a succession of episodic and time limited events happening in most if not all galaxies (Cavaliere & Padovani 1989; Collin-Souffrin 1991). The most plausible explanation for the onset of activity is fuelling of the nucleus by gas streaming towards the center of the galaxy as a result of interaction, accretion or merging events.

AGN surrounded by an extended emission line region are of particular interest since most often gas lying very far from the center is revealed by the ionizing flux from the active nucleus. Studying the kinematics and physical properties of this gas is a unique way towards disentangling the tight interaction between the gas motions and the nuclear activity (see e.g. the case of NGC 4388, where we have shown that the gas is certainly connected to the intracluster gas and that the source of ionization is not coincident with the optical nucleus, Petitjean & Durret 1993). In such studies, the knowledge of the host galaxy morphology is crucial since it strongly constrains the framework in which the observations should be analyzed (presence of a companion, distorsion of the disk, orientation and inclination of the galaxy).

A number of extended ionized nebulae have been detected with radii of the order of tens to hundreds of kpc from the nucleus itself (see catalogues by Durret 1989, and Heckman et al. 1991). The properties of these gaseous nebulae appear to be tightly correlated with the AGN activity, in particular with the UV and radio emission (McCarthy et al. 1987; Durret 1990), and the gas often suffers from important turbulent motions (Jorsäter et al. 1984; Bergeron et al. 1989; Heckman et al. 1991; Durret et al. 1994). Besides, the emission line widths are observed to increase with redshift (Heckman et al. 1991), implying that the properties of the gaseous nebulae evolve with redshift. For $z\approx 2$ the properties of the ionized gas around quasars and radio galaxies seem to be similar, as would be the case for similar objects seen from different viewing angles (Barthel 1989). However, an analysis of the IRAS data for a sample of radio quasars and radio galaxies has shown a systematic difference between the IR properties of these two types of objects (Heckman et al. 1992).

The morphologies of the host galaxies have been investigated by Hutchings (1987) through optical broad band images of radio galaxies and radio quasars; he concludes that 80% of them are interacting. However, for objects with redshifts of about 0.3, the [OIII]$\lambda$500.7 emission line is redshifted in the R band and can contribute most of the light. A striking example is TON 616 for which the [OIII]$\lambda$500.7 map (Durret et al. 1994) perfectly matches the R band image (Hutchings & McClure 1990). Near infrared imaging is not sensitive to young stellar populations, but on the contrary allows to sample mainly the old stellar population and can reveal unambiguously the structure of the underlying host. Moreover, near infrared images with a good spatial resolution in the K band are particularly well adapted to this purpose, since at these wavelengths the contributions of both dust and young ionizing stars are also minimized. The K band images will reveal the morphologies and near environments of the harboring galaxies, and allow us to connect the emitting gas morphology and kinematics (when available) with the potential of the underlying galaxy. In particular, such data should allow to study what kinds of perturbations could be invoked as the origin of the gas fuelling (presence of close companions, nonaxisymmetrical perturbations in accretion or merging events, or tidal interacting forces).

We present here observations in the J and K' bands of a sample of eleven quasars that were known to be associated with an extended ionized nebulosity. Three other nearby quasars (indicated with an ^* in Table 1) were included because they had extensions in their optical images which could be contaminated by ionized gas emission lines. Finally, A 0401-350A was observed serendipitously because it was in our redshift range and there was no object in our sample at this right ascension.

  

Table 1: Journal of observations

^a C=0.507''/pix, B=0.278''/pix.
^b No star in the frame.