issued by the American Astronomical Society

June 5, 2006 CALGARY -- Astronomers at the 208th American Astronomical Society meeting in Calgary announce the discovery of the most distant cluster of galaxies ever found, which may also be the most massive one yet seen at such an early era in the Universe. A cluster of galaxies is a large number of galaxies, gravitationally bound together, in a relatively small volume of space, all at the same distance from us.

"The key question now is: What's it doing there?" said Prof. Bob Nichol from the University of Portsmouth (England) and co-author on the paper. "This massive lump of matter is three-quarters the way back to the Big Bang!"

Almost 10 billion light-years from Earth (at a redshift z=1.45), cluster XMMXCS 2215-1738 contains hundreds of galaxies surrounded by superheated, X-ray-emitting gas at more than 10 million degrees. The XMM Cluster Survey (XCS) team used observations from the European X-ray Multi Mirror (XMM) Newton satellite to discovery this new cluster and then determined its distance using the 10-meter W. M. Keck telescope in Hawaii.

"I couldn't believe it when I saw that this distant cluster appears to be full of old galaxies" commented Adam Stanford, research scientist at UC Davis and at the Lawrence Livermore National Laboratory, and lead author on the discovery paper. "This cluster is a challenge for our models of how massive galaxies formed, and to our understanding of the way such a massive cluster exists at a relatively early era in the Universe."

"This cluster was not hard for us to find" notes Dr. Kathy Romer, Lecturer at the University of Sussex (England) and Principal Investigator of the international XCS team. The XCS is searching the XMM-Newton archive of observations for more clusters like XMMXCS 2215-1738, using algorithms developed by Dr Robert Mann, a lecturer at the University of Edinburgh. "This cluster was confirmed on our first good night at Keck, and we have 1000s more to look at. I can't wait to find out how many more clusters like XMMXCS 2215-1738 there are out there!" said Romer.

The real surprise of XMMXCS 2215-1738 may be its mass. Using the temperature of the X-ray emitting gas, Kivanc Sabirli, a graduate student at Carnegie Mellon University, determined that the cluster is approximately 500 trillion times the mass of our Sun.

Such massive clusters are expected to grow through the amalgamation of many smaller masses, like groups of galaxies. However, this process takes time. "Such a massive cluster at this early time in the Universe is only expected in a flat universe full of dark energy" states Dr. Pedro Viana, a cosmologist on the team from the University of Porto. "It is yet more evidence that we live in a strange Universe".

The XCS is embarked on a long-term observing program led by team member Chris Miller of the National Science Foundation's National Optical Astronomy Observatory (NOAO) to find more clusters like XMMXCS 2215-1738 using the 4-meter telescopes of the NOAO at both the Cerro Tololo Inter-American Observatory (CTIO) in Chile and the Kitt Peak National Observatory in Arizona. "We started well" commented Prof. Chris Collins from Liverpool Johns Moores University (England) and coordinating the observations of XCS clusters at other telescopes, such as the W. M. Keck 10-meter and Gemini 8-meter telescopes, "I expect the XCS to be the premier catalog of clusters for years to come".

That does not mean the team has already forgotten about XMMXCS 2215-1738. "It's special" said Stanford. "We will be studying this cluster using all the tools available to us - we are already getting detailed pictures using the Hubble Space Telescope". The galaxy cluster is a rare fossil of the early Universe and therefore will be treasured by astronomers.

Image may be obtained over the Internet at http://xcs-home.org/aas/

ADDITIONAL CONTACTS:

Kathy Romer
romer@sussex.ac.uk
+44 (0)1273 877478 (office)
+44 (0)7963 792046 (mobile)
Physics & Astronomy
University of Sussex
Brighton, BN1 9QH
United Kingdom

Bob Nichol
Bob.nichol@port.ac.uk
+44 (0)7963792049 (mobile)
Institute of Cosmology and Gravitation
Mercantile House, Hampshire Terrrace
University of Portsmouth
Portsmouth, PO1 2EG
United Kingdom

Chris Collins
cac@astro.livjm.ac.uk
+44 (0)1512 312918
Astrophysics Research Institute
Liverpool John Moores University
Twelve Quays House, Egerton Wharf
Birkenhead, CH41 1LD
United Kingdom

The research team includes: Adam Stanford (University of California, Davis and Lawrence Livermore National Laboratory) Kathy Romer (University of Sussex, UK) Kivanc Sabilri (Carnegie Mellon University) Michael Davidson (University of Edinburgh, UK) Matt Hilton (Liverpool John Moores University, UK) Pedro Viana (Porto, Portugal) Chris Collins (Liverpool John Moores University, UK) Scott Kay (Oxford University, UK) Andrew Liddle (University of Sussex, UK) Robert Mann (University of Edinburgh, UK) Chris Miller (Cerro Tololo Inter-American Observatory, NOAO, Chile) Bob Nichol (University of Portsmouth, UK) Mike West (Gemini Observatory, Chile and University of Hawaii) Christopher Conselice (University of Nottingham, UK) Hyron Spinrad (University of California, Berkeley) Daniel Stern (Jet Propulsion Laboratory) Kevin Bundy (California Institute of Technology) The work was funded by NASA, the Particle Physics and Astronomy Research Council (U.K.), the Hosie Bequest, and the National Science Foundation.