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             Information from the European Southern Observatory

ESO Press Release 17/03

19 June 2003                                               [ESO Logo]

For immediate release
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A First Look at the Doughnut Around a Giant Black Hole

Part 2 of 2

NGC 1068: a prototype AGN

NGC 1068 is among the brightest and most nearby active galaxies.
Located in the constellation Cetus at a distance of about 60 million
light years, it is also known as Messier 77. It is in fact one of the
biggest galaxies in Messier's catalogue and one of the first
recognised spiral galaxies. On optical images, NGC 1068 looks indeed
like a rather normal barred spiral galaxy. The core of the galaxy,
however, is very luminous not only in the optical, but also in
ultraviolet and X-ray light. A black hole with a mass equivalent to
approximately 100 million stars like our Sun is required to account
for the nuclear activity in NGC 1068. 


Fringes in the distant dust: resolving the torus in NGC 1068

The MIDI observations used two of the 8.2 m VLT unit telescopes (Antu
and Melipal), separated by a baseline of 102 m. Due to projection
effects, the actual baseline for the NGC 1068 observations amounted to
79 m. While observing NGC 1068, the astronomers detected
interferometric fringes (ESO PR Photo 18c/03). Fringes are produced
when beams of light from two telescopes are brought together exactly
in phase. For a point-like source, such fringes have the maximum
possible theoretical contrast (i.e. 100%): the source is unresolved.
However, sources of increasing angular size produce fringes with
decreasing contrast. In the case of NGC 1068, the measured contrast
was only about 10% of the maximum one. An exact interpretation of
this result will follow in the context of additional measurements
along different baselines, which are planned for this coming Autumn
[5]. Already this initial result is nevertheless very convincing: the
fringes were obtained with consistent values on several measurements
over 2 consecutive nights, thanks also to the excellent observing
conditions at the Paranal site ("seeing" values were between 0.3 and
0.6 arcsec). It is already possible to state that a structure on a
spatial scale of approximately 0.03 arcsec (corresponding to about 10
light-years) has been detected in the dust torus in NGC 1068. The
relative size of this structure is shown in ESO PR Photo 18b/03.


A breakthrough in interferometry

This measurement represents the first observation ever by the
technique of long-baseline interferometry of an extragalactic object
in the thermal infrared. This new success of the VLTI opens the door
to a completely new field in astronomy: the study of gas and dust
structures surrounding and feeding the biggest monsters in the
universe. MIDI and the VLTI will offer for years to come the best
combination for astronomers from all over the world to carry out
these studies. 


Notes

[1] More information about the VLTI and photos of many of the
components of the facility are available at the VLTI website, as well
as in ESO PR 06/01 ("First Light" in March 2001 and explanation of
the interferometric measurements), ESO PR 23/01 (observations with
two 8.2-m telescopes in October 2001) and ESO PR 16/02 (observations
with four 8.2-m telescopes in September 2002), ESO PR 22/02
(measurements of the diameters of small stars in November 2002) and
ESO PR 11/03 (installation of the first MACAO adaptive optics unit in
May 2003). 

[2]: The observations were planned and carried out by a team led by
Andrea Richichi (ESO) and including C. Leinert, R. Koehler, K.
Meisenheimer (MPIA), R. Waters (Amsterdam), F. Malbet (Grenoble), M.
Schoeller, S. Morel , F. Paresce, A. Glindemann, M.Tarenghi (ESO), H.
Roettgering and W. Jaffe (Leiden).

[3]: The MIDI instrument (http://www.mpia-hd.mpg.de/MIDI/) is the
result of a collaboration between German, Dutch and French
institutes. See ESO PR 25/02.

[4]: The AMBER instrument will equip the VLTI starting from 2004. It
will cover the 1-2.5 micron range, combining up to three different
telescopes. http://www.obs-nice.fr/amber/

[5]: NGC 1068 is well visible in September/October. The present
measurement was obtained under demanding pointing in June, in the very
last hour of the night.


Contacts

A. Richichi
ESO
Garching, Germany
Phone: +49 89 3200-6803
email: arichich{at}eso.org

C. Leinert [MIDI]
Max-Planck-Institut fur Astronomie
Heidelberg, Germany
Phone: +49 6221 528 264
email: leinert{at}mpia.de

H. Roettgering [NEVEC]
Leiden Observatory, The Netherlands
Phone: +31 71-5275851
email: rottgeri{at}strw.leidenuniv.nl

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