A new analysis of the nucleus of NGC 1068 with MIDI observations

Abstract

We present a new analysis of the very first mid-infrared N-band long-baseline interferometric observations of an extragalactic source: the nucleus of the Seyfert 2 galaxy NGC 1068, obtained with MIDI (Mid-InfrareD Interferometer), the mid-infrared beamcombiner at the European Southern Observatory (ESO) Very Large Telescope Interferometer (VLTI). The resolution of 10 mas allows to study the compact central core of the galaxy between 8 and 13 microns. Both visibility measurements and MIDI spectrum are well reproduced with a simple radiative transfer model with two concentric spherical components. The derived angular sizes and temperatures are about 35 and 83 mas, and 361 K and 226 K for these two components respectively. Some other evidences strongly support such low temperatures. This modeling also provides the variation of optical depth as a function of wavelength for the extended component across the N-band pointing towards the presence of amorphous silicate grains. This shows that MIDI actually carried out the first direct observations of the distribution of dust around the central engine. Together with other observational pieces, we are able to move a step forward in the reconstruction of the picture drawn for AGNs.