Old galaxies in a young universe: Finding stumps astronomers

01/05/04



Bright galaxies where stars are forming may outshine dimmer, more massive galaxies. In all previous surveys of the “Redshift Desert,” the brighter star-forming galaxies were the only type bright enough to be sampled. The Gemini Deep Deep Survey was able to sample the dimmer, more massive galaxies and provide a better representation of the galaxies at this epoch of the Universe. The GDDS results revealed that there is a greater abundance of these more massive and older galaxies than expected from current models when the Universe was only 20-40% of its current age.
Gemini Illustration by Jon Lomberg
Creditline “Gemini Observatory Illustration”

Full size image available here

Pasadena, California. "We expected to see small, young galaxies colliding and growing in the adolescent universe when it was about 20% to 40% of its present age," remarked Dr. Patrick McCarthy, Carnegie Observatories astronomer and co-principal investigator of the multinational Gemini Deep Deep Survey (GDDS)*. "It turns out, however, that the young universe was home to much older and more massive galaxies than we thought possible. I can't wait to see what the theoreticians will come up with to explain our observations."

Distant galaxies live far back in time and have been notoriously difficult to study. Not only are they dim because of their distance, the motion of the expanding universe makes it additionally problematic to capture their light and read the secrets of their spectra. A sophisticated technique called "Nod and Shuffle" has allowed scientists to break through this obstacle for the first time. It was developed by co-principal investigator of the survey, Dr. Karl Glazebrook of Johns Hopkins, and was used on the Gemini Multiobject Spectrograph on the 8-meter Gemini North telescope in Mauna Kea, Hawaii.

"We were able to collect spectra from over 300 galaxies initially identified in the Carnegie Las Campanas Infrared Survey completed in the late 1990s," ** explained McCarthy. "That survey collected infrared and optical colors of more than 100,000 galaxies to find the handful of massive, old galaxies in the early universe that we subsequently surveyed with Gemini. The Gemini group homed in on these far-away objects from the part of time we call the Redshift Desert--an era between 8 and 11 billion years ago that has been very difficult to observe. This survey is the most comprehensive study of galaxies in the early universe to date. It required over 120 total hours of telescope time and exposures that are about 10 times longer than is typical. The results have been simply startling."

"I think these results are extremely important," commented Dr. Wendy Freedman, director of the Carnegie Observatories. "There's absolutely no substitute for going out and looking at the universe to see what's actually there. The current best ideas suggest that it takes time for galaxies to assemble into the mature, beautiful objects we see today. But these exciting new observations suggest that the childhood, growth-phase of galaxies is accelerated. The Gemini group has shown us that our picture of how galaxies formed is not yet complete."

The findings were announced today at the 203nd meeting of the American Astronomical Society at the Hyatt Regency, 265 Peachtree St., NE, in Atlanta, Georgia. Papers from the study will be published in The Astrophysical Journal and The Astronomical Journal. Images are available at http://www.gemini.edu/gdds/

Source: Eurekalert & others

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