UKIRT, CFHT, and Chandra team up to unveil what could be the most distant galaxy cluster ever

CFHT image of the most distant cluster ever

The most distant cluster, JKCS041, 10.2 billion light years away. The concentration of reddish galaxies of JKCS041 stands up at the center of the image, and contrasts with bluish galaxies, sitting between us and JKCS041. Courtesy of CFHT/TERAPIX/WIRDS. Full resolution image is available at this URL

The most distant galaxy cluster ever has been discovered on a survey made by the United Kingdom Infrared Telescope, confirmed with a wealth of optical and infrared data, and its nature as a fully formed cluster revealed using NASA's Chandra X-ray Observatory. The cluster is located about 10.2 billion light years away, and is seen when the Universe was only about a quarter of its present age. Its discovery is being published in Astronomy & Astrophysics.

This newly discovered galaxy cluster, known as JKCS041, beats the previous record holder by over a billion light years. Galaxy clusters are some of the largest objects in the Universe. JKCS041 is found at the cusp of when scientists think galaxy clusters can form in the early Universe based on how long it should take for them to assemble.

"We have now the most basic information needed to study cluster galaxies at a very early epochs: where to point our telescopes," said Stefano Andreon of the National Institute for  Astrophysics (INAF) in Milano, Italy. "We can now study cluster galaxies that have 1/10th the age of galaxies near us and about half the age of galaxies in the previous distance record cluster."

The previous record holder for a galaxy cluster was 9.2 billion light years away, XMMXCS J2215.9-1738, discovered by ESA's XMM-Newton in 2006. This broke the previous distance record by only about 0.1 billion light years, while JKCS041 surpasses XMMXCS J2215.9 by about ten times that.

Galaxy clusters are often detected first with optical and infrared observations that reveal their component galaxies dominated by old, red stars. JKCS041 was originally detected in 2006 in a survey from the United Kingdom Infrared Telescope (UKIRT). The distance to the cluster was then determined from optical and infrared observations from UKIRT and the Canada-France-Hawaii Telescope in Hawaii, and the NASA's Spitzer Space Telescope.

Infrared observations are important because the optical light from the galaxies at large distances is shifted into infrared wavelengths because of the expansion of the universe and this part of the galaxy spectrum carries an important feature, the one used to infer the object distance.

The Chandra data were the final but crucial piece of evidence as it showed that JKCS041 was, indeed, a genuine galaxy cluster: the extended X-ray emission detected by Chandra testifies the presence of an hot intracluster medium, present in formed clusters and lacking in proto-clusters.

"Our success in detecting such a distant object shows how well our methods are working," said Andreon. "JKCS041 should give a re-newed momentum to future missions searching for clusters at very high redshift: the mere existence of JKCS041 demonstrates that we have yet to reach the boundaries of the knowable universe: very high redshift clusters do exist!"

Contact: S. Andreon ( stefano.andreon _at_, tel: +39-02-72320324)

The article to appear in Astronomy and Astrophysics,
JKCS 041: a colour-detected galaxy cluster at zphot = 1.9 with deep potential well as confirmed by X-ray data
by S. Andreon, B. Maughan, G. Trinchieri, and J. Kurk is available at this URL

Press releases also issued by INAF (in Italian) and Chandra