Andrew Yee[_1_]
May 12th 08, 04:54 PM
ESA News
http://www.esa.int
9 May 2008
The Antennae Galaxies found to be closer to us
New research on the Antennae Galaxies using the Advanced Camera for Surveys
onboard the NASA/ESA Hubble Space Telescope shows that this proto-typical
pair of interacting galaxies is in fact much closer to us than previously
thought -- at 45 million light-years instead of 65 million light-years.
The Antennae Galaxies are among the closest known merging galaxies. The
merging pair of galaxies, NGC 4038 and NGC 4039, began interacting a few
hundred million years ago, creating one of the most impressive sights in the
night sky. They are considered by scientists as the archetypal merging
galaxy system and are used as a standard against which to validate theories
about galaxy evolution.
An international group of scientists led by Ivo Saviane from the European
Southern Observatory has used Hubble's Advanced Camera for Surveys and Wide
Field Planetary Camera 2 to observe individual stars spawned by the colossal
cosmic collision in the Antennae Galaxies. They reached an interesting and
surprising conclusion. By measuring the colours and brightnesses of red
giant stars in the system, the scientists found that the Antennae Galaxies
are much closer to us than previously thought: residing at a distance of 45
million light-years instead of the previous best estimate of 65 million
light-years.
The team targeted a region in the relatively quiescent outer regions in the
southern tidal tail, away from the active central regions. This tail
consists of material thrown from the main galaxies as they collided. The
scientists needed to observe regions with older red giant stars to derive an
accurate distance. Red giants are known to reach a standard brightness,
which can then be used to infer their distance from the difference between
the intrinsic and observed brightness. The method is known as the tip of the
red giant branch (TRGB).
The proximity of the Antennae system means it is the best-studied galaxy
merger in the sky, with a wealth of observational data to be compared to the
predictions of theoretical models. Saviane says: "All aspiring models for
galaxy evolution must be able to account for the observed features of the
Antennae Galaxies, just as respectable stellar models must be able to match
the observed properties of the Sun. Accurate models require the correct
merger parameters, and of these, the distance is the most essential".
The previous canonical distance to the Antennae Galaxies was about 65
million light-years although values as high as 100 million light years have
been used. Our Sun is only eight light-minutes away from us, so the Antennae
Galaxies may seem rather distant, but if we consider that we already know of
galaxies that are more than ten thousand million light-years away, the two
Antennae Galaxies are really our neighbours.
The previous larger distance required astronomers to invoke some quite
exceptional physical characteristics to account for the spectacular system:
very high star-formation rates, supermassive star clusters, ultraluminous
X-ray sources etc. The new smaller distance makes the Antennae Galaxies less
extreme in terms of the physics needed to explain the observed phenomena.
For instance, with the smaller distance its infrared radiation is now that
expected of a "standard" early merging event rather than that of an
ultraluminous infrared galaxy. The size of the star clusters formed as a
consequence of the Antennae merger now agree with those of clusters created
in other mergers instead of being 1.5 times as large.
The Antennae Galaxies are named for the two long tails of stars, gas and
dust that resemble the antennae of an insect. These "antennae" are a
physical result of the collision between the two galaxies. Studying their
properties gives us a preview of what may happen when our Milky Way galaxy
collides with the neighbouring Andromeda galaxy in several thousand million
years. Although galaxy mergers today are not common, it is believed that in
the past they were an important channel of galaxy evolution. Therefore
understanding the physics of galaxy mergers is a very important task for
astrophysicists.
The Antennae are located in the constellation of Corvus, the Crow.
The findings appeared in the 1 May 2008 issue of The Astrophysical Journal.
Notes for editors
The Hubble Space Telescope is a project of international cooperation between
ESA and NASA.
The authors of the science paper are: Ivo Saviane (European Southern
Observatory), Yazan Momany (Osservatorio Astronomico di Padova, Italy), Gary
S. Da Costa (Research School of Astronomy and Astrophysics, Australia), R.
Michael Rich (Department of Physics and Astronomy, USA) and John E. Hibbard
(National Radio Astronomy Observatory, USA)
Image credit: NASA, ESA & Ivo Saviane (European Southern Observatory)
For more information:
Ivo Saviane
European Southern Observatory, Santiago, Chile
E-mail: isaviane @ eso.org
Gary S. Da Costa
Research School of Astronomy & Astrophysics, ANU, Australia
Tel: +61-2-6125-8913
Lars Lindberg Christensen
Hubble/ESA, Garching, Germany
Tel: +49-(0)89-3200-6306
[NOTE: Images and weblinks supporting this release are available at
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=42759 ]
http://www.esa.int
9 May 2008
The Antennae Galaxies found to be closer to us
New research on the Antennae Galaxies using the Advanced Camera for Surveys
onboard the NASA/ESA Hubble Space Telescope shows that this proto-typical
pair of interacting galaxies is in fact much closer to us than previously
thought -- at 45 million light-years instead of 65 million light-years.
The Antennae Galaxies are among the closest known merging galaxies. The
merging pair of galaxies, NGC 4038 and NGC 4039, began interacting a few
hundred million years ago, creating one of the most impressive sights in the
night sky. They are considered by scientists as the archetypal merging
galaxy system and are used as a standard against which to validate theories
about galaxy evolution.
An international group of scientists led by Ivo Saviane from the European
Southern Observatory has used Hubble's Advanced Camera for Surveys and Wide
Field Planetary Camera 2 to observe individual stars spawned by the colossal
cosmic collision in the Antennae Galaxies. They reached an interesting and
surprising conclusion. By measuring the colours and brightnesses of red
giant stars in the system, the scientists found that the Antennae Galaxies
are much closer to us than previously thought: residing at a distance of 45
million light-years instead of the previous best estimate of 65 million
light-years.
The team targeted a region in the relatively quiescent outer regions in the
southern tidal tail, away from the active central regions. This tail
consists of material thrown from the main galaxies as they collided. The
scientists needed to observe regions with older red giant stars to derive an
accurate distance. Red giants are known to reach a standard brightness,
which can then be used to infer their distance from the difference between
the intrinsic and observed brightness. The method is known as the tip of the
red giant branch (TRGB).
The proximity of the Antennae system means it is the best-studied galaxy
merger in the sky, with a wealth of observational data to be compared to the
predictions of theoretical models. Saviane says: "All aspiring models for
galaxy evolution must be able to account for the observed features of the
Antennae Galaxies, just as respectable stellar models must be able to match
the observed properties of the Sun. Accurate models require the correct
merger parameters, and of these, the distance is the most essential".
The previous canonical distance to the Antennae Galaxies was about 65
million light-years although values as high as 100 million light years have
been used. Our Sun is only eight light-minutes away from us, so the Antennae
Galaxies may seem rather distant, but if we consider that we already know of
galaxies that are more than ten thousand million light-years away, the two
Antennae Galaxies are really our neighbours.
The previous larger distance required astronomers to invoke some quite
exceptional physical characteristics to account for the spectacular system:
very high star-formation rates, supermassive star clusters, ultraluminous
X-ray sources etc. The new smaller distance makes the Antennae Galaxies less
extreme in terms of the physics needed to explain the observed phenomena.
For instance, with the smaller distance its infrared radiation is now that
expected of a "standard" early merging event rather than that of an
ultraluminous infrared galaxy. The size of the star clusters formed as a
consequence of the Antennae merger now agree with those of clusters created
in other mergers instead of being 1.5 times as large.
The Antennae Galaxies are named for the two long tails of stars, gas and
dust that resemble the antennae of an insect. These "antennae" are a
physical result of the collision between the two galaxies. Studying their
properties gives us a preview of what may happen when our Milky Way galaxy
collides with the neighbouring Andromeda galaxy in several thousand million
years. Although galaxy mergers today are not common, it is believed that in
the past they were an important channel of galaxy evolution. Therefore
understanding the physics of galaxy mergers is a very important task for
astrophysicists.
The Antennae are located in the constellation of Corvus, the Crow.
The findings appeared in the 1 May 2008 issue of The Astrophysical Journal.
Notes for editors
The Hubble Space Telescope is a project of international cooperation between
ESA and NASA.
The authors of the science paper are: Ivo Saviane (European Southern
Observatory), Yazan Momany (Osservatorio Astronomico di Padova, Italy), Gary
S. Da Costa (Research School of Astronomy and Astrophysics, Australia), R.
Michael Rich (Department of Physics and Astronomy, USA) and John E. Hibbard
(National Radio Astronomy Observatory, USA)
Image credit: NASA, ESA & Ivo Saviane (European Southern Observatory)
For more information:
Ivo Saviane
European Southern Observatory, Santiago, Chile
E-mail: isaviane @ eso.org
Gary S. Da Costa
Research School of Astronomy & Astrophysics, ANU, Australia
Tel: +61-2-6125-8913
Lars Lindberg Christensen
Hubble/ESA, Garching, Germany
Tel: +49-(0)89-3200-6306
[NOTE: Images and weblinks supporting this release are available at
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=42759 ]