Astronomers reveal the first detailed maps of galaxy distributionin the early universe (Forwarded)

University of California-Santa Cruz

Contact:
Tim Stephens, UC Santa Cruz
831-459-2495;

Robert Sanders, UC Berkeley
510-643-6998;

Laura Kraft, Keck Observatory
808-881-3827;

FOR IMMEDIATE RELEASE: July 17, 2003

Astronomers reveal the first detailed maps of galaxy distribution in the early
universe

SANTA CRUZ, CA -- Peering back in time more than 7 billion years, a team of
astronomers using a powerful new spectrograph at the W. M. Keck Observatory in
Hawaii has obtained the first maps showing the distribution of galaxies in the
early universe. The maps show the clustering of galaxies into a variety of
large-scale structures, including long filaments, empty voids, and dense groups
and clusters.

These maps are among the first results from the DEEP2 Redshift Survey, an
ongoing three-year project designed to study galaxies in the distant universe
over a volume comparable to recent surveys of the local universe. Using the new
DEIMOS (Deep Extragalactic Imaging Multi-Object Spectrograph) instrument at the
10-meter Keck II Telescope, this project is measuring the properties of distant
galaxies as well as mapping out their distribution in space. DEIMOS, which was
built precisely for this survey, allows simultaneous, detailed observations of
up to 150 galaxies at a time. By studying galaxies whose light has taken
billions of years to reach the Earth, the astronomers are effectively looking
far back in time.

"For the first time, we are getting a map of the universe as it was 7 billion
years ago, when it was roughly half the age it is now. Comparing these
observations with local surveys will yield direct clues to some of the most
profound mysteries of the universe, such as the nature of dark matter, the
nature of dark energy, and the origins of galaxies and quasars," said David Koo,
professor of astronomy and astrophysics at the University of California, Santa Cruz.

Koo is presenting the group's first findings Thursday at a meeting of the
International Astronomical Union (IAU) in Sydney, Australia. The DEEP2 survey is
a collaboration between astronomers at UC Santa Cruz, UC Berkeley, and several
other institutions, including the California Institute of Technology and
University of Hawaii. Marc Davis, professor of astronomy at UC Berkeley, is
principal investigator for the current phase of the DEEP2 project. Sandra Faber,
University Professor of astronomy and astrophysics at UCSC, led the team that
designed and built DEIMOS at the Lick Observatory laboratories at UCSC.

"The DEIMOS data are so extensive compared to previous results that we can
construct maps showing considerable large-scale structure, and we can see
differences in the clustering of different types of galaxies," Davis said.

The structures seen in these maps of distant galaxies are similar to structures
seen in the local universe, although DEEP2 shows them at an earlier stage of
development.

"We are watching the galaxy population grow into what it is today," said Alison
Coil, a graduate student at UC Berkeley who was the lead researcher on the
analysis of the maps.

The maps presented at the IAU meeting are the first detailed three-dimensional
pictures of the spatial distribution of galaxies in the early universe. They
show the locations of galaxies in the distant universe in three of the four
DEEP2 fields. Although the maps do not cover much area of the sky (observations
so far cover an area about four times the size of the full moon), they extend
very far along the line of sight, probing deep into the universe to reveal
objects that are very distant in both space and time. This is a different
strategy from current local surveys such as the Sloan Digital Sky Survey and the
2dF Survey, which cover very wide areas of the sky but probe much shorter
distances along the line of sight, Coil said.

"This survey is extremely deep. Not only are we seeing objects more than 7
billion light-years away, but the survey itself covers 2.5 billion light-years,
so we can see the evolution of the galaxy population within the DEEP2 survey, in
addition to comparing it with local surveys," she said.

Statistical tests indicate that the clustering seen in the DEEP2 maps is not as
strong as that seen in the local universe today, Coil said. Galaxies cluster
under the force of gravity, and this clustering grows with time as structures
get larger and exert stronger gravitational pulls, causing them to grow even
more. Regions of space with high densities will exert their gravitational
influence on surrounding galaxies, pulling them in toward the dense regions,
which become even more dense in the process. While these dense regions are
growing, empty voids are left behind where very few, if any, galaxies reside.

At the same time, the galaxies themselves are evolving: creating stars, forming
black holes at their centers, falling in toward each other, and often colliding
and merging to form larger galaxies. All of these processes can be seen in the
DEEP2 data, Coil said.

DEEP2 observations will eventually map the locations of some 60,000 galaxies at
distances of about 6 to 8 billion light-years. Seeing how the large-scale
structures made up of galaxies evolved over time is just one aspect of the
study. The researchers are also investigating the properties of the individual
galaxies: their ages, how bright they are, how much matter they contain, how
quickly they are forming stars, and so on.

"Our ability to, in effect, weigh these distant galaxies is a unique aspect of
our survey," Koo said. "Galaxy mass is a fundamental parameter for understanding
the formation and evolution of galaxies, and by having this dimension we can
study these questions with more precision than has been possible before."

Galaxies are represented on the maps with black or red symbols. The black points
are galaxies that appear to be forming new stars in abundance, while the red
points are galaxies that have little ongoing star formation, which generally are
also older and redder. These older galaxies are much more strongly clustered in
space than the star-forming galaxies. The researchers also found that galaxies
with red colors are more clustered than bluer galaxies, and brighter galaxies
cluster more strongly than fainter galaxies.

"These trends are similar to those seen in the local universe; but for the first
time we can see that they were already in place 7 billion years after the Big
Bang, before our own Sun and solar system had formed," Davis said.

This project was supported in part by grants from the National Science
Foundation (NSF). The DEIMOS spectrograph was funded by a grant from CARA (Keck
Observatory), by an NSF Facilities and Infrastructure grant, by the Center for
Particle Astrophysics, and by gifts from Sun Microsystems and the Quantum
Corporation. The DEEP2 Redshift Survey has been made possible through the
dedicated efforts of the DEIMOS staff at UC Santa Cruz who built the instrument
and the Keck Observatory staff who have supported it on the telescope.

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NOTES FOR REPORTERS

The DEEP2 maps of distant galaxies are available on the web at
http://astron.berkeley.edu/~acoil/deep/cone_plots/

Additional images are available at
http://www.ucolick.org/~raja/deep2_p...lease_fig1.gif
(Image credit: P. Guhathakurta, A. Coil, D. Koo).

The following members of the DEEP2 team are available for interviews:

David Koo, professor, UC Santa Cruz (attending IAU)
, 831-459-2130

Alison Coil, graduate student, UC Berkeley
, 510-642-0388 or 510-644-0454

Sandra Faber, professor, UC Santa Cruz
, 831-459-2944

Jeffrey Newman, postdoctoral researcher, UC Berkeley
, 510-547-0950 or 510-643-8700

Puragra (Raja) GuhaThakurta, professor, UC Santa Cruz
, 831-459-5169

Richard Ellis, professor, Caltech/Palomar Observatory (attending IAU)

(Marc Davis is currently unavailable due to illness.)

Additional information about DEIMOS is available in an earlier press release at
http://www.ucsc.edu/news_events/pres...07.deimos.html