Midsummer's Dream Galaxies (Forwarded)

ESO Education and Public Relations Dept.

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Text with all links and the photos are available on the ESO
Website at URL:

http://www.eso.org/outreach/press-re...hot-24-05.html
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Contact:
Henri Boffin, ESO
Phone: +49 89 3200 6222

For immediate release: 10 August 2005

ESO Press Photos 24a-b/05

Midsummer's Dream Galaxies

Images of Two Magnificent Spiral Galaxies from ESO Data
Archive

ESO PR Photo 24a/05 ESO PR Photo 24b/05
Spiral Galaxy NGC 4565 Spiral Galaxy Messier 83

How does the Galaxy in which we live look like?

It is almost certain that we will never be able to send a
probe out of our Milky Way to take a snapshot, in the same
way as the first satellites could do to give us striking
images of planet Earth. But astronomers do not need this
to imagine what our bigger home resembles. And they have
a pretty good idea of it.

The Milky Way with its several hundreds of billion stars is
thought to be a relatively flat disc -- 100,000 light-year
across [1] -- with a central bulge lying in the direction
of the constellation Sagittarius (The Archer) and six spiral
arms. The Milky Way has most probably also a central bar
made of young, bright stars.

If we can't take pictures of the Milky Way, we may photograph
others galaxies which astronomers think look similar to it.
The two galaxies presented here are just two magnificient
examples of barred spiral galaxies. One -- Messier 83 -- is
seen face-on, and the other -- NGC 4565 -- appears edge-on.
Together, they give us a nice idea of how the Milky Way may
appear from outer space.

These images are based on data obtained with the twin FORS1
and FORS2 (FOcal Reducer and Spectrograph) instruments
attached to two ESO's 8.2-m Unit Telescopes of the Very
Large Telescope Array located on Cerro Paranal. The data
were extracted from the ESO Science Archive Facility, which
contains approximately 50 Terabytes [2] of scientific data
and is, since April 1, 2005, open to the worldwide community.
These invaluable data have already led to the publication of
more than 1000 scientific papers. They also contains many nice
examples of beautiful astronomical objects which could be the
theme of as many midsummer's dreams.

NGC 4565

The first galaxy pictured here is NGC 4565 [3], which for
obvious reasons is also called the Needle Galaxy. First
spotted in 1785 by Uranus' discoverer, Sir William Herschel
(1738-1822), this is one of the most famous example of an
edge-on spiral galaxy and is located some 30 million light-
years away in the constellation Coma Berenices (Berenice's
Hair). It displays a bright yellowish central bulge that
juts out above most impressive dust lanes.

Because it is relatively close (it is only 12 times farther
away than Messier 31, the Andromeda galaxy, which is the major
galaxy closest to us) and relatively large (roughly one third
larger than the Milky Way), it does not fit entirely into the
field of view of the FORS instrument (about 7 x 7 arcmin2).

Many background galaxies are also visible in this FORS image,
giving full meaning to their nickname of "island universes".

Messier 83

If our Milky Way were to resemble this one, we certainly would
be proud of our home! The beautiful spiral galaxy Messier 83
[4] is located in the southern constellation Hydra (the Water
Snake) and is also known as NGC 5236 and as the Southern
Pinwheel galaxy. Its distance is about 15 million light-years.
Being about twice as small as the Milky Way, its size on the
sky is 11x10 arcmin2.

The image show clumpy, well-defined spiral arms that are rich
in young stars, while the disc reveals a complex system of
intricate dust lanes. This galaxy is known to be a site of
vigorous star formation.

Notes

[1]: A light-year is the distance that light travels in a
vacuum in a year -- about 9.46 million million kilometres.

[2]: 1 Terabyte = 10**12 byte = 1000 Gigabyte = 1 million
million byte.

[3]: "NGC" means "New General Catalogue" (of nebulae and
clusters) that was published in 1888 by J.L.E. Dreyer in
the "Memoirs of the Royal Astronomical Society".

[4]: French astronomer and comet hunter Charles Messier (1730-
1817) is the author of world famous "Catalog of Nebulae and
Star Clusters" containing more than 100 objects.

Technical information: PR Photo 24a/05 and 24b/05 are based
on data obtained by FORS1 and FORS2 at the VLT. They were
extracted from the ESO Science Archive and further processed
by Henri Boffin (ESO). These photos are based on exposures
made through four optical filters. For PR Photo 24a/05,
these were B, V, R and I. For PR Photo 24b/05, the broad-band
filters B, I and R were used together with a narrow optical
filter that isolates light emitted by hydrogen in the red
H-alpha spectral line. It shows predominantly star-forming
regions and other emission nebulae, most of which are located
along the spiral arms. The field size is about 7 x 7 arcmin2.
North is down and East is right for PR Photo 24a/05, while
North is up and East is left for PR Photo 24b/05. Another
image of Messier 83 based on part of these data is available
at ESO Press Release 18/99 while an image of the same galaxy
obtained in the near-infrared is available at ESO Press
Photos 32a-b/01.

National contacts for the media:

Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Terhi Loukiainen, +358 9 7748 8385
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: Prof. Massimo Capaccioli, +39-081-55 75 511
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
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

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