Editor's Summary
14 September 2006
The oldest known galaxy
The galaxy described on page 186 may be, for the moment, the most distant and hence oldest galaxy known. Large samples of galaxies have been found at redshifts of z
6, but detections at earlier times tend to be uncertain and unreliable. But this 'new' old galaxy has a spectroscopic redshift of z=6.96, corresponding to just 750 million years after the Big Bang; and a Lyman-
emission line in its spectrum suggests that active star formation was under way when the Universe was only about 6% of its present age. This galaxy was detected during a survey using the Subaru Suprime-Cam on the summit of Mauna Kea. Looking at the galaxy population as a whole, the same survey produced a number density of galaxies at z
7 that is only 18-36% that at z=6.6. A separate search for galaxies at at z7–8 using data from the Hubble Space Telescope yielded (conservatively) only one candidate galaxy, where 10 would be expected if there were no evolution in the galaxy population between z7 and z6. The simplest explanation for this is that the Universe is just too young to have built up many luminous galaxies at z7–8 by hierarchical merging of small galaxies.
News: Journey to the birth of the Universe
Record-breaking galaxy found.
Jenny Hogan
doi:10.1038/443128a
News and Views: Astronomy: Dawn after the dark age
The latest surveys provide evidence for one, maybe two, galaxies farther back in cosmic time than ever detected before. But does the fact that we don't see more mean these are the very first galaxies to be formed?
Richard McMahon
doi:10.1038/443151a
Letter: A galaxy at a redshift z = 6.96
Masanori Iye, Kazuaki Ota, Nobunari Kashikawa, Hisanori Furusawa, Tetsuya Hashimoto, Takashi Hattori, Yuichi Matsuda, Tomoki Morokuma, Masami Ouchi and Kazuhiro Shimasaku
doi:10.1038/nature05104
First paragraph | Full Text | PDF (269K)
Letter: Rapid evolution of the most luminous galaxies during the first 900 million years
Rychard J. Bouwens and Garth D. Illingworth
doi:10.1038/nature05156
First paragraph | Full Text | PDF (258K) | Supplementary information