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Astron. Astrophys. 353, 465-472 (2000)

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1. Introduction

Series of observational facts assembled over the past decade on Active Galactic Nuclei have led to the so-called "unified" model of AGN (for a review of these facts, as well as for the detailed characteristics of the unified model see Krolik 1999). Our current specific interest in the unified model is that the central engine (black hole and accretion disk) and its close environment (dense gas clouds emitting the broad lines which constitute the broad line region, BLR) are embedded within an optically thick dusty/molecular torus. Along some lines of sight, the torus obscures and even fully hides the central engine and the BLR.

In that respect, the case of NGC 1068 , a bright Seyfert 2 active galaxy, is particularly enlightening. The spectrophotometry in polarized light reveals the presence of a hidden BLR (Antonucci & Miller 1985), the conical shape of the narrow line region (NLR) - both on large (Pogge 1988) and small (Evans et al. 1991) scales - indicates that the ionizing radiation is collimated by an opaque blocking torus and, finally, the symmetry center of the UV/optical polarization map (Capetti et al. 1995) is found to be coincident with the radio core (Gallimore et al. 1996a), the 12.4µm peak (Braatz et al. 1993) and the maser emission (Gallimore et al. 1996b), suggesting that this is the location of the hidden true nucleus.

This object appears then particularly suitable for unveiling the putative torus through its infrared emission, which, according to current models should be quite strong (e.g. Pier & Krolik 1992a, b, 1993; Granato & Danese 1994; Efstathiou et al. 1995; Granato et al. 1997). In this search, high spatial resolution is a requisite in order to locate very precisely and to characterize the structure of emission sources. Hence, adaptive optics (hereafter abbreviated AO) in the 1-5µm window is the tool. At the distance of NGC 1068 (14.4 Mpc), 1" is equivalent to 72 pc (assuming H0=75 km/s/Mpc), allowing us to reach a spatial resolution of a few parsecs. Through AO observations, simultaneously in the visible and near-infrared, the 2.2µm peak emission has already been found to be offset by [FORMULA] 0.3" S of the optical continuum peak as defined by Lynds et al. (1991) and to be coincident with the previously identified "hidden true nucleus" (Marco et al. 1997). In the current study, we are presenting new results obtained at 3.5 and 4.8µm with ADONIS, the AO system working at the ESO 3.6 m telescope on La Silla and fully described in Beuzit et al. (1994).

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999