Ancient City of Galaxies Looks Surprisingly Modern

Ancient City of Galaxies Looks Surprisingly Modern

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-157&cid=release_2010-157

Astronomers are a bit like archeologists as they dig back through space and time searching for
remnants of the early universe. In a recent deep excavation, courtesy of NASA's Spitzer Space
Telescope, astronomers unearthed what may be the most distant, primitive cluster of galaxies ever
found.

In a twist, however, this apparent ancestor to today's "big cities" of grouped galaxies looks
shockingly modern. Called CLG J02182-05102, the ancient cluster is dominated by old, red and
massive galaxies, typical of present-day clusters. For example, it is similar to a young version of
the Coma Cluster of today, which has had billions of more years to develop.

"We are seeing something already aged and red like a younger version of the Coma Cluster from
a distant, bygone era," said Casey Papovich, lead author of a new study and an assistant
professor of physics and astronomy at Texas A&M University in College Station.

Papovich added, "it is as though we dug an archeological site in Rome and found pieces of
modern Rome in amongst the ruins."

ClG J02182-05102 might have indeed been ahead of its time. Just as Rome was the world's
biggest city more than 2,000 years ago with a population of about a million residents – a figure
not again matched until the early 1800s in London – so too was this galactic grouping an
advanced civilization for so early an era in the developing universe.

Galaxy clusters are the largest gravitationally bound structures in the universe and are thought to
have formed piecemeal over cosmic time. For now, ClG J02182-05102 is the only known galactic
grouping so far away in the past, and studying it will help researchers understand the overall
history of how galaxies congregate and evolve.

A Cosmic Archeological Expedition

In their hunt for rare ancient cities in the early universe, Papovich and his team started with the
largest extragalactic survey ever made. Called the Spitzer Wide-area InfraRed Extragalactic
(SWIRE) survey, it observed a huge portion of the sky that could contain 250 full moons.

Because more light gathered means more information, the researchers looked at a cosmic region
within this giant starscape that had also been studied by other instruments. These additional
observations came from a survey combining light from Japan's Subaru telescope – housed atop
Mauna Kea, Hawaii – and the European Space Agency's orbiting XMM-Newton telescope. The
United Kingdom Infra-Red Telescope, also in Hawaii, provided infrared data along with another
set of Spitzer observations called the Public Ultra Deep Sky survey.

When all these data were compiled, Spitzer's infrared observations made dozens of distant
galaxies jump out. "We would not have found this object without Spitzer because there is very
little optical light coming from this group of galaxies," said Papovich.

His team then obtained time on the Magellan telescope in Chile to study the faint light coming
from ClG J02182-05102's least-dim galaxies. This light allowed the astronomers to
archeologically date the candidate cluster to 9.6 billion years ago.

With these observations, Papovich and his team confirmed that seven of ClG J02182-05102's
galaxies have nearly the same distance, suggesting they are part of a grouping of about 60
galaxies. Whether or not this association of galaxies fully qualifies as a gravitationally bound
cluster will rely on further observations. Furthermore, the definition of a "cluster" itself remains
unsettled, somewhat like the blurry distinctions between a city and a town, made trickier still
given the limited light that makes it to our telescopes from these relics.

The Rise and Fall of CLG J02182-05102

For now, ClG J02182-05102 stands out as a greatly over-dense region of galaxies – a metropolis
in a land of isolated villages. At its center regions loom red, monster galaxies containing about 10
times as many stars as our Milky Way galaxy. This puts them on par with the most mammoth
galaxies in the nearby universe, which have grown fat through repeated mergers with other
galaxies. These big galaxies are so uncharacteristic of those in the early universe that in some
sense it is like finding modern skyscrapers in ancient Rome.

The Papovich et al paper was accepted for publication in the Astrophysical Journal on April 21,
2010. A subsequent study by Masayuki Tanaka of the Institute for the Physics and Mathematics
of the Universe in Japan confirmed the discovery, and the work was the subject of a news release
on May 10, 2010.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope
mission for NASA's Science Mission Directorate, Washington. Science operations are conducted
at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech
manages JPL for NASA.

#2010-157

-end-

Contact: Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory
whitney.clavin@jpl.nasa.gov

Written by Adam Hadhazy

To remove yourself from this mailing, please go to http://www.kintera.org/TR.asp?a=juIUK5PPLlKTKhL&s=kuJ2L7ONJgLOI6MTJuH&m=dwISJ8PSKgKYIqI

To remove yourself from all mailings from NASA Jet Propulsion Laboratory, please go to http://www.kintera.org/TR.asp?a=cdJGLKMnFeJGIXK&s=kuJ2L7ONJgLOI6MTJuH&m=dwISJ8PSKgKYIqI