Astrophysicists Discover Massive Forming Galaxies in Young Galaxy Clusters

Sept. 17, 2003

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-red shift 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-red shift 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 red shifts, 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 red shift suggests that the scientists may have witnessed this process for the first time.

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