Andrew Yee
September 1st 05, 01:47 AM
Office of Public Affairs and Educational Outreach
National Optical Astronomy Observatory
Tucson, Arizona
For More Information:
Douglas Isbell
Office of Public Affairs and Educational Outreach
National Optical Astronomy Observatory
Phone: 520/318-8230
FOR IMMEDIATE RELEASE: Tuesday, August 30, 2005
RELEASE NO: NOAO 05-08
Survey of 4,000 Galaxies Finds "Downsizing" on a Cosmic Scale
A comprehensive survey of more than 4,000 elliptical and lenticular
galaxies in 93 nearby galaxy clusters has found a curious case of galactic
"downsizing."
Contrary to expectations, the largest, brightest galaxies in the census
consist almost exclusively of very old stars, with much of their stellar
populations having formed as long ago as 13 billion years. There appears
to be very little recent star formation in these galaxies, nor is there
strong evidence for recent ingestion of smaller, younger galaxies.
By contrast, the smaller, fainter galaxies studied by the NOAO Fundamental
Plane Survey are significantly younger -- their stars were formed as
little as four billion years ago, according to new results from the survey
team to be published in the September 10, 2005, Astrophysical Journal.
These findings are based on a sample more than five times larger than
previous efforts. The results of the survey contrast sharply with
conventional hierarchical model of galaxy formation and evolution, where
large elliptical galaxies in the nearby universe formed by swallowing
smaller galaxies with young stars; this theory predicts that, on average,
the stars in the largest elliptical galaxies should be no older than those
in the smallest ones.
"This sample probes the largest and richest galaxy clusters in the nearby
universe, out to a distance of about a billion light-years from Earth,"
says Jenica Nelan, lead author of the study. "Our analysis shows that
there is a clear relationship between mass and age in these red galaxies,
meaning that the stars in the biggest, oldest galaxies that we studied
formed early in the history of the Universe. On average, the smaller
galaxies have one-tenth the mass of the larger ones, and are only about
half their age."
"The term 'downsizing' essentially means that when the Universe was young,
the star formation activity occurred in large galaxies, but as the
Universe aged, the 'action' stopped in the larger galaxies, even as it
continued in smaller galaxies," says Michael Hudson of the University of
Waterloo, Ontario, Canada, principal investigator for the NOAO Fundamental
Plane Survey.
The new study is based on thousands of spectra obtained by the Fundamental
Plane Survey team over dozens of nights at the WIYN 3.5-meter telescope at
Kitt Peak National Observatory, southwest of Tucson, AZ, and the National
Science Foundation's Blanco 4-meter telescope at Cerro Tololo
Inter-American Observatory, east of La Serena, Chile. With some
painstaking work, these spectra can reveal the average age of the stars
that make up a galaxy.
"Although we cannot directly see these galaxies as they were in the past,
their stars are a kind of 'fossil record' that can be used to unearth
their histories," Hudson explains. "It appears that the older galaxies are
much less of a 'melting pot' than had been thought, and that their star
formation activity turned off somehow while they were being put together."
The evolutionary history of elliptical galaxies and lenticular galaxies
(which have a central bulge and a disk, but no evidence of spiral arms) is
not well understood. Their colors appear to be "redder" than typical
spiral galaxies. The largest ellipticals are the reddest of all, but until
this work it has not been clear whether this property results primarily
from being older in age, as the survey found, or from having a higher
proportion of heavy chemical elements (metallicity content).
"These so-called red galaxies contain the bulk of the stellar mass in the
nearby universe, but we know little about their formation and evolution,"
says co-author Russell Smith of the University of Waterloo. "It was
thought that all of the red galaxies were made of stars that formed very
early, and are now quite old. Our results show that while this is true for
the large galaxies, the smaller ones formed their stars comparatively
recently in the history of the Universe. We predict that as new surveys
look deeper and hence further into the past, they should see fewer faint
red galaxies."
An image of galaxy cluster Abell 3266 taken by survey team members at the
Gemini South telescope as part of their follow-up work is available above.
Lead author Jenica Nelan completed this work while earning her doctorate
at Dartmouth College; she is now an astronomer at Yale University.
Co-authors of this paper include Hudson and Smith of the University of
Waterloo; Gary Wegner of Dartmouth College; John R. Lucey, Stephen A. W.
Moore, and Stephen J. Quinney of the University of Durham, and Nicholas B.
Suntzeff of NOAO's Cerro Tololo Inter-American Observatory.
The Fundamental Plane Survey is one of 18 projects granted long-term
access to observing nights at the telescope of the National Optical
Astronomy Observatory (NOAO) under the NOAO Survey Program.
See here for more information:
http://www.noao.edu/gateway/surveys/programs.html
and
http://astro.uwaterloo.ca/~mjhudson/nfp
Based in Tucson, AZ, NOAO is operated by the Association of Universities
for Research in Astronomy (AURA) Inc., under a cooperative agreement with
the National Science Foundation.
IMAGE CAPTION:
This image of galaxy cluster Abell 3266 was taken using the Gemini
Multi-Object Spectrograph (GMOS) instrument on the Gemini South telescope
on Cerro Pachón, Chile, in July 2005. The image was obtained by the NOAO
Fundamental Plane Survey team as part of follow-up observations in support
of their spectroscopic data from Kitt Peak National Observatory and Cerro
Tololo Inter-American Observatory.
Abell 3266 is located at a distance of 250 million light-years from Earth.
It is one of the most populous galaxy clusters in the nearby universe, and
one of 93 clusters that were the subject of an August 2005 NOAO press
release. Galaxy clusters contain mostly red elliptical galaxies, as seen
in this view of the central region of Abell 3266.
Image Credit: Michael Hudson and Russell Smith (University of Waterloo)
and Gemini Observatory
Download:
* A3266.tif [2346x1458, 19.6 MB]
http://www.noao.edu/outreach/press/pr05/images/A3266.tif
* A3266.jpg [2346x1458, 388 KB]
http://www.noao.edu/outreach/press/pr05/images/A3266.jpg
* A3266_1200.jpg [1200x756 121 KB]
http://www.noao.edu/outreach/press/pr05/images/A3266_1200.jpg
National Optical Astronomy Observatory
Tucson, Arizona
For More Information:
Douglas Isbell
Office of Public Affairs and Educational Outreach
National Optical Astronomy Observatory
Phone: 520/318-8230
FOR IMMEDIATE RELEASE: Tuesday, August 30, 2005
RELEASE NO: NOAO 05-08
Survey of 4,000 Galaxies Finds "Downsizing" on a Cosmic Scale
A comprehensive survey of more than 4,000 elliptical and lenticular
galaxies in 93 nearby galaxy clusters has found a curious case of galactic
"downsizing."
Contrary to expectations, the largest, brightest galaxies in the census
consist almost exclusively of very old stars, with much of their stellar
populations having formed as long ago as 13 billion years. There appears
to be very little recent star formation in these galaxies, nor is there
strong evidence for recent ingestion of smaller, younger galaxies.
By contrast, the smaller, fainter galaxies studied by the NOAO Fundamental
Plane Survey are significantly younger -- their stars were formed as
little as four billion years ago, according to new results from the survey
team to be published in the September 10, 2005, Astrophysical Journal.
These findings are based on a sample more than five times larger than
previous efforts. The results of the survey contrast sharply with
conventional hierarchical model of galaxy formation and evolution, where
large elliptical galaxies in the nearby universe formed by swallowing
smaller galaxies with young stars; this theory predicts that, on average,
the stars in the largest elliptical galaxies should be no older than those
in the smallest ones.
"This sample probes the largest and richest galaxy clusters in the nearby
universe, out to a distance of about a billion light-years from Earth,"
says Jenica Nelan, lead author of the study. "Our analysis shows that
there is a clear relationship between mass and age in these red galaxies,
meaning that the stars in the biggest, oldest galaxies that we studied
formed early in the history of the Universe. On average, the smaller
galaxies have one-tenth the mass of the larger ones, and are only about
half their age."
"The term 'downsizing' essentially means that when the Universe was young,
the star formation activity occurred in large galaxies, but as the
Universe aged, the 'action' stopped in the larger galaxies, even as it
continued in smaller galaxies," says Michael Hudson of the University of
Waterloo, Ontario, Canada, principal investigator for the NOAO Fundamental
Plane Survey.
The new study is based on thousands of spectra obtained by the Fundamental
Plane Survey team over dozens of nights at the WIYN 3.5-meter telescope at
Kitt Peak National Observatory, southwest of Tucson, AZ, and the National
Science Foundation's Blanco 4-meter telescope at Cerro Tololo
Inter-American Observatory, east of La Serena, Chile. With some
painstaking work, these spectra can reveal the average age of the stars
that make up a galaxy.
"Although we cannot directly see these galaxies as they were in the past,
their stars are a kind of 'fossil record' that can be used to unearth
their histories," Hudson explains. "It appears that the older galaxies are
much less of a 'melting pot' than had been thought, and that their star
formation activity turned off somehow while they were being put together."
The evolutionary history of elliptical galaxies and lenticular galaxies
(which have a central bulge and a disk, but no evidence of spiral arms) is
not well understood. Their colors appear to be "redder" than typical
spiral galaxies. The largest ellipticals are the reddest of all, but until
this work it has not been clear whether this property results primarily
from being older in age, as the survey found, or from having a higher
proportion of heavy chemical elements (metallicity content).
"These so-called red galaxies contain the bulk of the stellar mass in the
nearby universe, but we know little about their formation and evolution,"
says co-author Russell Smith of the University of Waterloo. "It was
thought that all of the red galaxies were made of stars that formed very
early, and are now quite old. Our results show that while this is true for
the large galaxies, the smaller ones formed their stars comparatively
recently in the history of the Universe. We predict that as new surveys
look deeper and hence further into the past, they should see fewer faint
red galaxies."
An image of galaxy cluster Abell 3266 taken by survey team members at the
Gemini South telescope as part of their follow-up work is available above.
Lead author Jenica Nelan completed this work while earning her doctorate
at Dartmouth College; she is now an astronomer at Yale University.
Co-authors of this paper include Hudson and Smith of the University of
Waterloo; Gary Wegner of Dartmouth College; John R. Lucey, Stephen A. W.
Moore, and Stephen J. Quinney of the University of Durham, and Nicholas B.
Suntzeff of NOAO's Cerro Tololo Inter-American Observatory.
The Fundamental Plane Survey is one of 18 projects granted long-term
access to observing nights at the telescope of the National Optical
Astronomy Observatory (NOAO) under the NOAO Survey Program.
See here for more information:
http://www.noao.edu/gateway/surveys/programs.html
and
http://astro.uwaterloo.ca/~mjhudson/nfp
Based in Tucson, AZ, NOAO is operated by the Association of Universities
for Research in Astronomy (AURA) Inc., under a cooperative agreement with
the National Science Foundation.
IMAGE CAPTION:
This image of galaxy cluster Abell 3266 was taken using the Gemini
Multi-Object Spectrograph (GMOS) instrument on the Gemini South telescope
on Cerro Pachón, Chile, in July 2005. The image was obtained by the NOAO
Fundamental Plane Survey team as part of follow-up observations in support
of their spectroscopic data from Kitt Peak National Observatory and Cerro
Tololo Inter-American Observatory.
Abell 3266 is located at a distance of 250 million light-years from Earth.
It is one of the most populous galaxy clusters in the nearby universe, and
one of 93 clusters that were the subject of an August 2005 NOAO press
release. Galaxy clusters contain mostly red elliptical galaxies, as seen
in this view of the central region of Abell 3266.
Image Credit: Michael Hudson and Russell Smith (University of Waterloo)
and Gemini Observatory
Download:
* A3266.tif [2346x1458, 19.6 MB]
http://www.noao.edu/outreach/press/pr05/images/A3266.tif
* A3266.jpg [2346x1458, 388 KB]
http://www.noao.edu/outreach/press/pr05/images/A3266.jpg
* A3266_1200.jpg [1200x756 121 KB]
http://www.noao.edu/outreach/press/pr05/images/A3266_1200.jpg