Using the unprecedented power of adaptive optics combined
with the 10-meter (400 inch) Keck II telescope, UCLA astronomers and Center for
Adaptive Optics (CfAO membersTiffany Glassman and Dr. James Larkin are peering
into the distant universe to discover what our own Milky Way galaxy might have
been like at the time our sun was forming.
The observations are an important step forward in the process
of understanding how galaxies formed and how they evolved into the wide variety
"For the first time, we're able to get very detailed
images in a survey of distant galaxies in the infrared," said Larkin, associate
professor of astronomy at UCLA speaking at the annual meeting of the American
Astronomical Society. "These new measurements will help pin down the details
of galaxy evolution, and they show that adaptive optics will play an important
role in understanding galaxy formation billions of years ago."
The ten galaxies observed are about 5 billion light years
from earth (redshift of about 0.5), a period when the universe was about two-thirds
of its present age. This time span represents a significant portion of the lifetime
of a galaxy and is far enough back to begin to discriminate between different
theories of galaxy formation.
"This is an important first step in gaining much more
information about galaxies in the early universe," said Glassman, graduate
student in astronomy at UCLA. "Though our current sample is small and the
results preliminary, our only clue towards an understanding of how galaxies -
like our own Milky Way - form is to look further and further into the past, and
adaptive optics promises to be one of the best ways to do that."
Galaxies are among the largest cohesive structures in the
universe, often consisting of more than 100 billion stars. At great distances,
however, even these vast structures appear as only small smudges through the world's
largest ground-based telescopes.
Adaptive optics (AO) allows astronomers to remove much of
the blurring effects of the earth's atmosphere and achieve sharper images
than any previously taken. These sharper images allow the sizes of galaxies, as
well as the properties of smaller components that make up each galaxy, to be studied.
Glassman and Larkin observed galaxies whose dominant components
are a large, flattened disk and a central, spherical bulge, similar to the Milky
Way and other nearby spiral galaxies. With AO the same basic properties (size
and brightness of the disks and bulges) can be measured for the distant galaxies
they observed and for local galaxies.
The astronomers can now compare these properties to see how
the galaxies have changed over billions of years. They found that as a group the
disks of the distant galaxies are 2.5 times brighter at their center and 20% smaller
than local disks. A less quantitative analysis of the galaxies' bulges showed
that their central brightness also fades by about a factor of 2 but their size
stays relatively constant.
The results produced by Glassman and Larkin support other
observations and theories that indicate that large galaxies were primarily assembled
more than 10 billion years ago and are slowly fading as a group as the rate of
new star formation declines.
To continue their research, Glassman and Larkin are building
a much larger sample of galaxies including many at significantly greater distances.
This survey is possible because of a new camera for the Keck Telescope's
Adaptive Optics system called NIRC2 (Near Infrared Camera 2) which has been available
to the researchers since July through the cooperation of the camera team led by
Keith Matthews of Caltech.
NIRC2 has a much larger field of view and is significantly
more sensitive than the earlier cameras and greatly improves the quality of the
data available to Glassman and Larkin. "This new sample should allow for
more detailed comparisons between local and distant galaxies, but perhaps more
importantly it will contain a small number of galaxies seen just after their initial
formation," said Glassman. "Detailed images like these, of galaxies
in their infancy, will give astronomers the best handle on how galaxies first
hown above are two, false-color images of the same galaxy, both taken with the
10-meter Keck Telescope by UCLA astronomers Tiffany Glassman and Dr. James Larkin.
The image on the left was taken without Adaptive Optics and shows the usual limit
on the detail that can be seen with ground-based telescopes. The image on the
right was taken with the Keck Adaptive Optics system and shows the vast improvement
in the sharpness of the image and the detail than can be seen. This galaxy, located
in the constellation Pegasus, is 4 billion light years from Earth (redshift of
0.37). A basic disk and bulge structure can be seen, as well as a central bar,
a smaller point source that might be a satellite galaxy, and the hint of spiral
arms in the disk. With detailed images of distant galaxies like this one, astronomers
can learn more about what the universe was like billions of years ago. This material
was presented to the American Astronomical Society meeting in Washington, DC on
January 7, 2002. PHOTO CREDIT: UCLA, Department of Physics and Astronomy: T. Glassman
& J. Larkin.