Mar. 21, 2005 Pasadena, CA -- Astronomers have found distant red galaxies—very massive and very old—in the universe when it was only 2.5 billion years post Big Bang. “Previous observations suggested that the universe at this age was home to young, small clumps of galaxies long before they merged into massive structures we see today,” remarked Carnegie Observatories Ivo Labbé, who led the group of astronomers in the study.* “We are really amazed—these are the earliest, oldest galaxies found to date. Their existence was not predicted by theory and it pushes back the formation epoch of some of the most massive galaxies we see today."
About two years ago, astronomers from Leiden (The Netherlands) using the European ground-based Very Large Telescope found a population of distant red galaxies in the near infrared. But the images could not ascertain what made the galaxies red: Were they old and “dead” and no longer forming stars, or were massive amounts of dust obscuring star-forming regions?
The Labbé-led group used the infrared-imaging Spitzer Space Telescope to analyze the content of the new galactic population to address the questions of age, stellar mass, and activity. Giovanni Fazio (Harvard-Smithsonian Center for Astrophysics), a co-author on the study, said, "Spitzer offers capabilities that the Hubble Space Telescope and other instruments don't, giving us a unique way to study very distant galaxies long ago that eventually became the galaxies we see around us now."
The team was particularly surprised to find very old, red galaxies that had stopped forming new stars altogether. They had rapidly formed massive amounts of stars out of gas much earlier in the universe's history, but then suddenly starved to death, raising the question of what caused them to die so early. Such "red and dead" galaxies may be the forefathers of some of the old and giant elliptical galaxies seen in the local universe today.
In addition to the old "dead” galaxies long past star formation, there were other red, dusty galaxies still vigorously producing stars. Jiasheng Huang (Harvard-Smithsonian Center for Astrophysics) said, "We're detecting galaxies we never expected to find, having a wide range of properties we never expected to see." Apparently, the early universe was already a wildly complex place. "It's becoming more and more clear that the young universe was a big zoo with animals of all sorts," continued Labbé. "There's as much variety in the early universe as we see around us today."
Ultimately, these studies will help to unravel how galaxies like our Milky Way assembled and how they got to look the way they appear today. The research will be published in an upcoming issue of The Astrophysical Journal (Letters).
Carnegie Observatories: http://www.ociw.edu/
More information on Spitzer can be found at: http://www.spitzer.caltech.edu/spitzer/index.shtml
* Researchers on the project were Ivo Labbé, Carnegie Observatories; Jiasheng Huang, Harvard-Smithsonian Center for Astrophysics; Marijn Franx, Leiden Observatory; Gregory Rudnick, NOAO; Pauline Barmby, Harvard-Smithsonian Center for Astrophysics, Emanuele Daddi, NOAO; Pieter G. van Dokkum, Yale University; Giovanni G. Fazio, Harvard-Smithsonian Center for Astrophysics; Natascha Forster Schreiber Max Plank-Institute für extraterrestrische Physik; Alan Moorwood, ESO; Hans-Walter Rix, Max-Plank-Institute für Astronomie; Huub Röttgering NOAO; Ignaciao Trujillo, Max-Plank-Institute für Astronomie; Paul van der Werf, Leiden Observatory.
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