07 November 2008
For immediate release
A Pool of Distant Galaxies the deepest ultraviolet image of the Universe
Anyone who has wondered what it might be like to dive into a pool of millions
of distant galaxies of different shapes and colours, will enjoy the latest image
released by ESO. Obtained in part with the Very Large Telescope, the image is
the deepest ground-based U-band image of the Universe ever obtained. It contains
more than 27 million pixels and is the result of 55 hours of observations with
the VIMOS instrument.
ESO PR Photo 39/08
A Pool of Distant GalaxiesThis uniquely beautiful patchwork image, with its
myriad of brightly coloured galaxies, shows the Chandra Deep Field South (CDF-S),
arguably the most observed and best studied region in the entire sky. The CDF-S
is one of the two regions selected as part of the Great Observatories Origins
Deep Survey (GOODS), an effort of the worldwide astronomical community that
unites the deepest observations from ground- and space-based facilities at all
wavelengths from X-ray to radio. Its primary purpose is to provide astronomers
with the most sensitive census of the distant Universe to assist in their study
of the formation and evolution of galaxies.
The new image released by ESO combines data obtained with the VIMOS instrument
in the U- and R-bands, as well as data obtained in the B-band with the Wide-Field
Imager (WFI) attached to the 2.2 m MPG/ESO telescope at La Silla, in the framework
of the GABODS survey.
The newly released U-band image the result of 40 hours of staring at
the same region of the sky and just made ready by the GOODS team is the
deepest image ever taken from the ground in this wavelength domain. At these
depths, the sky is almost completely covered by galaxies, each one, like our
own galaxy, the Milky Way, home of hundreds of billions of stars.
Galaxies were detected that are a billion times fainter than the unaided eye
can see and over a range of colours not directly observable by the eye. This
deep image has been essential to the discovery of a large number of new galaxies
that are so far away that they are seen as they were when the Universe was only
2 billion years old.
In this sea of galaxies or island universes as they are sometimes called
only a very few stars belonging to the Milky Way are seen. One of them
is so close that it moves very fast on the sky. This "high proper motion
star" is visible to the left of the second brightest star in the image.
It appears as a funny elongated rainbow because the star moved while the data
were being taken in the different filters over several years.
Just click on the image above to see it in full resolution!
The Chandra Deep Field South, observed in the U-, B-, and R-bands with ESO's
VIMOS and WFI instruments. The U-band VIMOS observations were made over a period
of 40 hours and constitute the deepest image ever taken from the ground in the
U-band. The image covers a region of 14.1 x 21.6 arcmin on the sky and shows
galaxies that are 1 billion times fainter than can be seen by the unaided eye.
The VIMOS R-band image was assembled by the ESO/GOODS team from archival data,
while the WFI B-band image was produced by the GABODS team.
Credit: ESO/ Mario Nonino, Piero Rosati and the ESO GOODS Team
Because the Universe looks the same in all directions, the number, types and
distribution of galaxies is the same everywhere. Consequently, very deep observations
of the Universe can be performed in any direction. A series of fields were selected
where no foreground object could affect the deep space observations (such as
a bright star in our galaxy, or the dust from our Solar System). These fields
have been observed using a number of telescopes and satellites, so as to collect
information at all possible wavelengths, and characterise the full spectrum
of the objects in the field. The data acquired from these deep fields are normally
made public to the whole community of astronomers, constituting the basis for
Observations in the U-band, that is, at the boundary between visible light and
ultraviolet are challenging: the Earth's atmosphere becomes more and more opaque
out towards the ultraviolet, a useful property that protects people's skin,
but limiting to ground-based telescopes. At shorter wavelengths, observations
can only be done from space, using, for example, the Hubble Space Telescope.
On the ground, only the very best sites, such as ESO's Paranal Observatory in
the Atacama Desert, can perform useful observations in the U-band. Even with
the best atmospheric conditions, instruments are at their limit at these wavelengths:
the glass of normal lenses transmits less UV light, and detectors are less sensitive,
so only instruments designed for UV observations, such as VIMOS on ESO's Very
Large Telescope, can get enough light.
The VIMOS U-band image, which was obtained as part of the ESO/GOODS public programme,
is based on 40 hours of observations with the VLT. The VIMOS R-band image was
obtained co-adding a large number of archival images totaling 15 hours of exposure.
The WFI B-band image is part of the GABODS survey.
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