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Two distant galaxies provide new puzzles.

Astronomers exploring the nature of galaxy formation and evolution have shed new light on two of the most distant galaxies known in the universe. Both bodies were initially identified by their unusually intense radio emissions, and both lie so far away from Earth that astronomers observe them as they appeared billions of years ago, when the universe was just 10 percent of its current age. Nonetheless, the galaxies sport several differences.

"It's like looking at a roomful of babies ranging from 1 day to 1 year old," says Mark Dickinson of the University of California, Berkeley. "A small difference in age can make a big difference in appearance -- and in the case of galaxies, not all were born at the same time."

One of the two studies examined in unprecedented detail the radio galaxy 4C 41.17, the most distant galaxy ever observed. Using the Hubble Space Telescope, George K. Miley of Leiden University in the Netherlands and his colleagues discovered that the galaxy's core has a chain of luminous clumps that are aligned with its jets of radio emissions. Miley suggests that these clumps are knots of star formation triggered by the high-intensity radio jets. Alternatively, he says, the clumps may not be stars at all. Instead, they may represent light scattered by gas or dust caught in the searchlight of a bright energy source -- possibly a quasar -- buried at the galaxy's center. Miley says his team will need further Hubble observations, examining 4C 41.17 at a second wavelength, to decide between the two possibilities.

In studying another distant radio galaxy, B2 0902+34, which lies only slightly closer to Earth, Dickinson and Peter R. Eisenhardt of the Jet Propulsion Laboratory in Pasadena, Calif., have solved an old puzzle. The researchers began their ground-based infrared study after astronomer Simon J. Lilly, now at the University of Toronto, reported that although the galaxy is observed soon after the birth of the universe, it has very red stars -- indicating that the stars are more than 1 billion years old (SN: 4/23/88, p.262). That finding spells trouble for most cosmology theories, which can't explain how a galaxy could have evolved so rapidly after the Big Bang.

Eisenhardt and Dickinson now report that Lilly's view of B2 0902+34 was colored by the red glow of ionized oxygen gas in the galaxy. They say that the stars at the center of the galaxy are actually bluer, and thus younger, than believed -- no more than 300 million years old. Indeed, B2 0902+34 could be a proto-galaxy, a galaxy caught in the act of formation, the researchers report in the Nov. 1 ASTROPHYSICAL JOURNAL LETTERS. In contrast to 4C 41.17, light from the galaxy is not aligned with its radio emissions, they note. In addition, B2 0902+34 has a somewhat younger star population and a blobby, less elongated shape.

The study also revealed an unsettling finding. The team detected what appears to be a bright red halo around B2 0902+34. If the halo is confirmed, it suggests that stars at the outskirts of the galaxy are redder, and possibly older, than those at the core -- a phenomenon never before observed.
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Title Annotation:4C 41.17, B2 09021+34
Author:Cowen, Ron
Publication:Science News
Date:Nov 14, 1992
Words:533
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