Hot Very Small dust Grains in NGC 1068 seen in jet induced structures
thanks to VLT/NACO adaptive optics
ArXiv astro-ph/0312094 (2003)
Authors:
Daniel Rouan, Francois Lacombe, Eric Gendron, Damien Gratadour, Yann Clenet, Anne-Marie Lagrange, David Mouillet, Catherine Boisson, Gerard Rousset, Laurent Mugnier, Niranjan Thatte, Reinhard Genzel, Pierre Gigan, Robin Arsenault, Pierre Kern
Abstract:
We present K, L and M diffraction-limited images of NGC 1068 obtained with
NAOS+CONICA at VLT/YEPUN over a 3.5" field around the central engine. Hot dust
(Tcol = 550-650 K) is found in three different regions : (a) in the true
nucleus, seen as a slightly NS elongated, core of extremely hot dust,
"resolved" in K and L with respective diameters of ~5 pc and 8.5 pc ; (b) along
the NS direction, as a "spiral arm" and a southern tongue ; (c) as a set of
parallel elongated nodules ("wave-like") bracketting the jet. Several
structures observed on radio maps, mid-IR or HST UV-visible maps are seen, so
that a precise registration can be done from UV to 6 cm. These results do
support the current interpretion that source (a) corresponds to emission from
dust near sublimation temperature delimiting the walls of the cavity in the
central obscuring torus. Structure (b) is thought to be a mixture of hot dust
and active star forming regions along a micro spiral structure that could trace
the tidal mechanism bringing matter to the central engine. Structure c)which
was not known, exhibits too high a temperature for "classical'' grains ; it is
most probably the signature of transiently heated very small dust grains (VSG)
: "nano-diamonds", which are resistant and can form in strong UV field or in
shocks, are very attractive candidates. The "waves'' can be condensations
triggered by jet induced shocks, as predicted by recent models. First
estimates, based on a simple VSG model and on a detailed radiative transfer
model, do agree with those interpretations, both qualitatively and
quantitatively.
