Hidden slice of
universe is revealed

Astronomers on Mauna Kea
use a new detector to open another
window on the history of galaxies

By Helen Altonn
Star-Bulletin

Astronomers from Hawaii and Japan have found a hidden population of distant star-forming galaxies by using a unique detection instrument.

Although obscured by dust, the invisible galaxies are putting out as much light as those seen with optical telescopes, said Len Cowie, University of Hawaii Institute for Astronomy associate director and researcher.

"We have to work hard on this to see how much it's going to change things," he said. "It's going to change the historical record of galaxy formation."

Collaborating with Japanese astronomers, Cowie and institute colleagues Dave Sanders, Amy Barger and Eliza Fulton made the discovery with the James Clerk Maxwell Telescope operated by the United Kingdom, Canada and the Netherlands on Mauna Kea. It will be announced in tomorrow's edition of the journal Nature.

A unique instrument on the millimeter/submillimeter telescope called SCUBA (Submillimeter Common User Bolometer Array) opened the window to the hidden region, Cowie said.

Barger said, "The only way we can come up with a comprehensive understanding of the universe is if we look through all available windows."

And submillimeter astronomy offers an entirely different view than optical astronomy, she pointed out. "The objects we're targeting are different beasts than we've already seen."

No one has been able to see these galaxies because they're very distant, and telescopes haven't been sensitive enough, she said. It was possible only recently with the revolutionary SCUBA, Barger said.

Cowie said the instrument, developed for over more than a decade at the Royal Observatory in Edinburgh, was put on the radio telescope about a year ago.

Until recently, he said, astronomers had to look for distant objects at optical wavelengths, but many objects are concealed by a screen of dust.

The new submillimeter detector looks beyond the dust at colder, longer wavelengths.

"We all knew once we got this, there was a good possibility we would see this other class of objects," Cowie said.

"With SCUBA, you can actually go in and see the individual object producing that light, and you can see individual galaxies contributing to that."

What wasn't well known, he said, was how much energy from star formation is being put out in optical or submillimeter regions, or how many "hidden" galaxies there are compared to the ones that could be seen. "It turns out they're quite comparable."

"What this says is, this is a whole other species we're going to have to take into account," Cowie added. "And there are a lot of them."

Richard Ellis, Institute of Astronomy director at the University of Cambridge in the United Kingdom, said the observations have opened a new era in cosmological exploration.

"Understanding this new population is essential in order to obtain a comprehensive picture of cosmic galaxy formation," he said.

Cowie believes astronomers will be able to understand the process and map the dusty galaxies after a few more years of work.

"We're going to be banging away on this. It's really exciting."

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For more information: http://www.ifa.hawaii.edu/~cowie/scuba/scuba_int.html