NEW METHOD USED TO PROBE GALAXY ORIGINS.

Byline: Jane E. Allen Associated Press 

Astronomers have used a new technique to identify the most distant group of infant galaxies that are likely ancestors of bright galaxies like the Milky Way.

By looking into deep space - and back in time - the team made direct observations of 23 galaxies as they appeared soon after they formed, about 12.8 billion to 13.5 billion years ago. The universe is thought to have been created by the Big Bang about 15 billion years ago.

"We know that at some point in the early history of the universe, galaxies came together and formed out of a primordial soup. Until now, we really didn't know exactly when that happened," said Chuck Steidel, an assistant astronomy professor at the California Institute of Technology in Pasadena.

"For the first time, we can actually study what an average galaxy looked like at a time soon after its formation," he said Friday in an interview from an observatory atop Mt. Palomar.

With the new technique, "we've found a means of discovering an entire population of galaxies, rather than just one or two."

The research has been accepted for publication this spring in Astrophysical Journal Letters, a journal of the American Astronomical Society.

In related news, a team at the University of Colorado announced Friday that it had observed a distant galaxy in the process of being born. That galaxy, believed to be the brightest ever observed, is about 10 billion years old and 100 times brighter than the Milky Way, which contains our solar system. The research led by assistant professor Erica Ellingson will appear in the May issue of the Astronomical Journal.

Galaxies are round or football-shape conglomerations of 10 billion to 100 billion stars formed when interstellar gas collapses.

The 23 distant, infant galaxies that Steidel and his team observed "basically look like compact little balls of forming stars. They look like those parts of today's galaxies that we know have the oldest stars in them," Steidel said.

Astronomers dated the galaxies using a technique that takes images of the sky with filters that let through only particular wavelengths of light.

The galaxies could be seen through red filters and green filters. But when ultraviolet filters were used, the galaxies disappeared. That provided an indication of distance, which correlates to age in astronomy.

The astronomers next used a stronger telescope, the W.M. Kick Telescope on Mauna Kea in Hawaii, to get a more precise age. They analyzed each galaxy's spectrum and something called its redshift. The higher the redshift, the further away and older it is. The galaxies analyzed had redshifts of 3 to 3.5.

Steidel said the team has identified more than 100 additional potential distant galaxies.

The color technique allowed the astronomers to make observations through a larger range of distance in a single viewing than previous methods. On some nights, they were able to locate 30 to 40 galaxies.

Steidel said the galaxies were seen in three or four different areas of the sky.

"This method will work no matter which way we point the telescope," he said.

The research was funded by grants from the National Science Foundation, Alfred P. Sloan Foundation, and the National Aeronautics and Space Administration.