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 e.g. Antonucci, 1992).
Our specific interest in the unified model is that the central engine (black hole and accretion disk or compact starburst region) 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 may obscure and even fully hide the central engine and BLR.
As a straightforward conclusion, we are naturally led to search for the torus through its infrared emission, which, according to current models should be quite strong (Pier & Krolik, 1992b; Efstathiou & Rowan-Robinson, 1995; Granato & Danese, 1994; Granato et al., 1996, 1997): the near-infrared spectral energy distribution of most AGN shows a bump peaking at 3-5 µm (Edelson & Malkan, 1986; Robson et al., 1986), and a torus with a mean dust temperature of T 800 K would give rise to a peak in the L band (3.5 µm). In this search, high spatial resolution is imperative in order to locate very precisely the torus emission: hence, adaptive optics in the 1-5 µm window is the tool.
As a bright Seyfert 1 galaxy, NGC 7469 is well suited for the study of the dust component. Its proximity, 66 Mpc (H0=75 km/s/Mpc), its brightness (mv13 for the unresolved core used by the wavefront analysis sensor) allows to observe it with an adaptive optics system at a resolution down to 110 pc (0.35") at 3.8 µm . Observations had been made previously in the near-infrared 1-2.2 µm (Genzel et al., 1995), analysing the nuclear gas and the 500 pc radius starburst ring. In the current study, we are presenting new results obtained with adaptive optics at 3.5 and 3.8µm , with a special attention to the very central source (r1.4").
© European Southern Observatory (ESO) 1998
Online publication: July 27, 1998