Weekly Science Update

Wednesday, May 02, 2007
Star Formation in the Distant Universe
In the northern sky, not far from the handle of the Big Dipper, lies a patch of the heavens that is relatively dark, that is to say, free of bright stars and the diffuse glow of the Milky Way. For the past ten years this region, known as the Extended Groth Strip (EGS: named for Princeton University physicist Edward Groth), has been studied meticulously by groups of astronomers who want to take advantage of the clarity of the region to look beyond our galaxy to remote galaxies in the distant cosmos.

When Edwin Hubble and his colleagues compiled their study of nearby galaxies nearly eighty years ago, their discoveries revolutionized our concept of the universe. They found that what had been imagined to be an eternal and static cosmos was in fact an expanding universe, formed in a big bang, whose galaxies were in outward motion. The galaxies in the EGS are much more remote than Hubble's objects - so distant in fact that their light has been traveling towards us for eleven billion years or more - over 80% of the age of the universe. Astronomers engaged in the study of these distant objects in the EGS wonder about conditions in the early universe, but also about what new surprises might be in store.

The May 1 issue of the Astrophysical Journal Letters is devoted to nineteen papers on the All-Wavelength EGS International (AEGIS) survey. This undertaking by nearly 100 scientists from ten instrument teams in six countries brings together data from all major wavelength bands, from the X-ray to the radio, to study the distant galaxies found in the EGS. SAO astronomers co-authored nine of these nineteen papers, and the SAO-led Infrared Array Camera (IRAC) on the Spitzer Space Telescope was one of the key facilities used. In one of the papers, a group of seven SAO astronomers, Jiasheng Huang, Matthew Ashby, Steve Willner, Pauline Barmby, Howard Smith, and Giovanni Fazio, report on a galaxy that IRAC had discovered to be ultraluminous due to what was thought to be intensive star formation activity underway. In nearby galaxies such starbursts are characterized by infrared emission signature of small dust grains heated by the ultraviolet light of new stars. Because galaxies in the expanding universe are moving away from us, all such features in their received light are shifted to longer wavelengths. In this particular AEGIS study, the features are seen at four times their normal wavelength, making this galaxy the most distant known object in which these diagnostic features have been seen. The results not only help to explain the nature these luminous galaxies, they also help to identify the epochs in the cosmic evolution when stars began to be produced in massive numbers.

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