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Surveying the universe's middle-aged galaxies. (Sky Prospecting).



With a year's worth of data now in hand from a telescope survey of thousands of galaxies 6 to 8 billion light-years away, astronomers are filling in details about the midlife mid·life
n.
See middle age.

adj.
Of, relating to, or characteristic of middle age.
 years of the nearly 14-billion-year-old universe.

"We're looking back in time," says Alison Coil of the University of California, Berkeley The University of California, Berkeley is a public research university located in Berkeley, California, United States. Commonly referred to as UC Berkeley, Berkeley and Cal . "The light we're seeing traveled for [at least] 6 billion years before it reached our telescope."

The new results come from the first year of a 3-year sky survey, which is the second phase of a project known as the Deep Extragalactic ex·tra·ga·lac·tic  
adj.
Located or originating beyond the Milky Way.

Adj. 1. extragalactic - outside or beyond a galaxy; "extragalactic nebula"
 Evolution Probe. In DEEP2, Coil and her colleagues are mapping galaxies within four distant, cone-shaped sections of the universe that are each about 9.5 billion light-years deep. Viewed from Earth, the base at the far end of each section is about the size of the full moon. The researchers presented their first findings last week at the annual meeting of the International Astronomical Union “IAU” redirects here. For other uses, see IAU (disambiguation).

The International Astronomical Union (IAU) unites national astronomical societies from around the world.
 in Sydney, Australia.

"This survey provides the first detailed picture of what galaxies looked like and how they were clustered when the universe was about half its present age," comments Martin Rees, an astronomer at the University of Cambridge in England. In another major project, the Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico. The project was named after the Alfred P.  (SN: 5/31/03, p. 341), astronomers are scanning more-local neighborhoods of galaxies and the universe's outer limits--but not the vast stretches in between.

In the DEEP2 survey, Coil and her colleagues are examining how galaxies evolve by measuring their mass, motion, and chemical makeup and the ages of their stars. Clues to all these specifications can be gleaned from the different wavelengths of light that a galaxy emits. Using the telescope's Deep Imaging Multi-Object Spectrograph, or DEIMOS, the astronomers split the faint light from distant galaxies into separate wavelengths, just as a prism separates white light into distinct colored bands.

"Spectra are the Rosetta stone Rosetta Stone: see under Rosetta.
Rosetta Stone

Inscribed stone slab, now in the British Museum, that provided an important key to the decipherment of Egyptian hieroglyphs.
 for understanding celestial objects," says Sandra Faber, an astrophysicist at the University of California, Santa Cruz The University of California, Santa Cruz, also known as UC Santa Cruz or UCSC, is a public, collegiate university, one of the ten campuses of the University of California.  and a member of the DEEP2 team. For example, a bluish blu·ish also blue·ish  
adj.
Somewhat blue.



bluish·ness n.
 tinge is the signature of a galaxy crowded with young stars, while galaxies with an older stellar population radiate ra·di·ate
v.
1. To spread out in all directions from a center.

2. To emit or be emitted as radiation.



ra
 more red light.

The DEEP2 team used red and blue light emissions to compare the clustering behavior of galaxies that are 6 to 8 billion light-years away to that of nearer galaxies. In both groups, galaxies containing mostly young stars don't clump as much as galaxies with older stars do. Overall, however, galaxies from the universe's midlife epoch show more clumping than do younger galaxies--supporting the theory that gravity increases clustering over time.

By the end of the survey, the DEEP2 scientists plan to have mapped 50,000 galaxies from the universe's middle years. Rees says that this cache of data should help refine theories about how the universe has evolved.

Also, Coil notes, knowing the masses of that many galaxies could enable astronomers to better discern the distribution of so-called dark matter--one of the driving forces behind the overall geometry and motion of galaxies.
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Author:McDonagh, S.
Publication:Science News
Geographic Code:1USA
Date:Jul 26, 2003
Words:505
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