Astrophysicists Discover Massive Forming Galaxies in Young GalaxyClusters (Forwarded)

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FOR IMMEDIATE RELEASE: September 17, 2003

NR-03-09-05

Astrophysicists Discover Massive Forming Galaxies in Young Galaxy Clusters

LIVERMORE, Calif. -- A Lawrence Livermore National Laboratory astrophysicist, in
collaboration with international researchers, has found evidence for the
synchronous formation of massive, luminous elliptical galaxies in young galaxy
clusters.

The forming galaxies were detected at sub-millimeter wavelengths. Emission at
these wavelengths is due to dust from young stars that is heated by the stars or
by active black holes. The galaxies were grouped around high-redshift radio
galaxies, the most massive systems known, suggesting that they all formed at
approximately the same time.

In the present universe, the most massive galaxies are elliptical galaxies,
which are found in the centers of rich galaxy clusters. The stars in these
galaxies are now old, and must have formed at much earlier times. The enormous
bursts of star formation that build these galaxies produce large quantities of
dust that can be observed at submillimeter wavelengths.

Wil van Breugel, of Livermore's Institute of Geophysics and Planetary Physics,
along with scientists from the University of Edinburgh, the University of
Durham, Instituto Nacional de Astrofiscia and Leiden Observatory in The
Netherlands, present their research, "The Formation of Cluster Elliptical
Galaxies as Revealed by Extensive Star Formation," in the Sept. 18 edition of
Nature.

Earlier sub-millimeter studies of high-redshift radio galaxies have shown that
their star-formation rates are large enough to build a massive galaxy. However,
that research provided no information on the spatial extent of the emission or
on the star-formation in their environments. By mapping seven objects with
varying redshifts, the team was able to illustrate the distribution of
dust-reradiated emission in and around the radio galaxies.

"One of the most striking aspects of these maps is that we can see that the dust
emission from the central radio galaxy is very extended, the size of many times
the diameter of our own galaxy," van Breugel said. "But even more interesting is
that we also found other massive forming galaxies near these radio galaxies,
suggesting that they all started their formation at approximately the same time."

Models of galaxy formation show that the most massive galaxies form in overdense
regions that then form clusters of galaxies. The discovery of groups of
luminous, dusty galaxies at high redshift suggests that the scientists may have
witnessed this process for the first time.

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