Anatomy of a Bird: VLT's NACO instrument reveals a triple cosmiccollision (Forwarded)

ESO Education and Public Relations Dept.

Contacts

Petri Väisänen
South African Astronomical Observatory
Cape Town, South Africa
Phone: +27-21-460-9354 (office)

Seppo Mattila
Tuorla Observatory, University of Turku, Finland
Phone: +358 2 333 8299

For Immediate Release: 21 December 2007

ESO Press Photo 55/07

----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at
URL:
http://www.eso.org/public/outreach/p.../pr-55-07.html
----------------------------------------------------------------------------

Anatomy of a Bird

VLT's NACO instrument reveals a triple cosmic collision

Using ESO's Very Large Telescope, an international team of astronomers [1]
has discovered a stunning rare case of a triple merger of galaxies. This
system, which astronomers have dubbed 'The Bird' -- albeit it also bears
resemblance with a cosmic Tinker Bell -- is composed of two massive spiral
galaxies and a third irregular galaxy.

The galaxy ESO 593-IG 008, or IRAS 19115-2124, was previously merely known
as an interacting pair of galaxies at a distance of 650 million
light-years. But surprises were revealed by observations made with the
NACO instrument attached to ESO's VLT, which peered through the
all-pervasive dust clouds, using adaptive optics to resolve the finest
details [2].

Underneath the chaotic appearance of the optical Hubble images --
retrieved from the Hubble Space Telescope archive -- the NACO images show
two unmistakable galaxies, one a barred spiral while the other is more
irregular.

The surprise lay in the clear identification of a third, clearly separate
component, an irregular, yet fairly massive galaxy that seems to be
forming stars at a frantic rate.

"Examples of mergers of three galaxies of roughly similar sizes are rare,"
says Petri Väisänen, lead author of the paper reporting the results. "Only
the near-infrared VLT observations made it possible to identify the triple
merger nature of the system in this case."

Because of the resemblance of the system to a bird, the object was dubbed
as such, with the 'head' being the third component, and the 'heart' and
'body' making the two major galaxy nuclei in-between of tidal tails, the
'wings'. The latter extend more than 100,000 light-years, or the size of
our own Milky Way.

Subsequent optical spectroscopy with the new Southern African Large
Telescope, and archive mid-infrared data from the NASA Spitzer space
observatory, confirmed the separate nature of the 'head', but also added
further surprises. The 'head' and major parts of the 'Bird' are moving
apart at more than 400 km/s (1.4 million km/h !). Observing such high
velocities is very rare in merging galaxies. Also, the 'head' appears to
be the major source of infrared luminosity in the system, though it is the
smallest of the three galaxies.

"It seems that NACO has caught the action right at the time of the first
high-speed fly-by of the 'head' galaxy through the system consisting of
the other two galaxies," says Seppo Mattila, member of the discovery team.
"These two galaxies must have met earlier, probably a couple of hundred
million years ago."

The 'head' is forming stars violently, at a rate of nearly 200 solar
masses per year, while the other two galaxies appear to be at a more
quiescent epoch of their interaction-induced star formation history.

The 'Bird' belongs to the prestigious family of luminous infrared
galaxies, with an infrared luminosity nearly one thousand billion times
that of the Sun. This family of galaxies has long been thought to signpost
important events in galaxy evolution, such as mergers of galaxies, which
in turn trigger bursts of star formation, and may eventually lead to the
formation of a single elliptical galaxy.

The findings presented here are reported in a paper to appear in a future
issue of the journal Monthly Notices of the Royal Astronomical Society
("Adaptive optics imaging and optical spectroscopy of a multiple merger in
a luminous infrared galaxy", by P. Väisänen" et al.).

Note

[1]: The team is composed of P. Väisänen, A. Kniazev, D. A. H. Buckley, L.
Crause, Y. Hashimoto, N. Loaring, E. Romero-Colmenero, and M. Still (SAAO,
South Africa), S. Mattila (Tuorla Observatory, Finland), A. Adamo and G.
Östlin (Stockholm University, Sweden), A. Efstathiou (Cyprus College,
Nicosia, Cyprus), D. Farrah (Cornell University, USA), P. H. Johansson
(Universitäts-Sternwarte München, Germany), E. B. Burgh and K. Nordsieck
(University of Wisconsin, USA), P. Lira (Universidad de Chile, Santiago,
Chile), A. Zijlstra (University of Manchester, UK ), and S. Ryder (AAO,
Australia).

[2]: The final resolution was better than a tenth of an arcsecond, that
is, the angle sustained by a 2-cm coin seen from a distance of 40 km. This
is roughly a factor 600 better than what a keen human eye can distinguish.

National contacts for the media:

Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Czech Republic: Pavel Suchan, +420 267 103 040
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vørnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Spain: Dr. Miguel Mas-Hesse, +34918131196
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
USA: Dr. Paola Rebusco, +1-617-308-2397

----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------