February 16, 2005

ALFALFA Project Surveys Galaxies

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The Arecibo telescope, the world’s largest and most sensitive single-dish radio telescope, stationed in Puerto Rico, began to administer a more advanced method of surveying galaxies up to 800 million light years away two weeks ago. The telescope is a part of the National Astronomy and Ionosphere Center (NAIC), operated by Cornell University in cooperation with the National Science Foundation.

By means of a new instrument named the Arecibo Legacy Fast Arecibo L-Band Seed Array (ALFALFA), the radio telescope is making broad and blind sweeps of the entire galaxy that is visible from Puerto Rico. It is looking for galaxies that emit only radio waves and cannot be optically seen. The telescope enables researchers to measure the amount of hydrogen gas in the local universe.

Martha P. Haynes, Goldwin Smith Professor of Astronomy, flew to Puerto Rico yesterday to help conduct observations at the telescope. She explained that the radio telescope would allow researchers to map out the hydrogen gas that exists in the galaxy. Once completed, this information would give the researchers an estimate of how fast objects are rotating, how distant they are and the total amount of matter that is in the universe.

Sabrina Stierwalt grad said that such information could confirm what is known as the “cold dark matter theory,” a theory which states that certain low-mass halos form around other galaxies that optical telescopes would not be able to detect.

“It’s a matter of matching the observations with the theory,” said Brian Kent grad, who will be focusing on studying the HI mass function, a hydrogen-gas graph that ALFALFA will produce with the information collected from the survey. According to Kent, even in preliminary observations since it first began surveying the sky on Feb. 4, the Arecibo telescope has already detected more low-mass halos than researchers have seen ever before.

ALFA, Haynes explained, is essentially a camera that “detects signals from seven spots at the same time … [making] Arecibo much more efficient. We can look for very faint signals over a large part of the sky much faster than before.” The telescope can detect very weak cosmic signals that most other telescopes cannot distinguish from radio noise.

In the past, Arecibo has been used for a large range of research, including studying the earth’s upper atmosphere, to radar observations of the Moon, to Saturn’s rings, to studies of pulsars, to star formations in the Milky Way.

“Among other things, we’ll want to do deeper studies of ALFALFA discoveries to try to learn more about them. ALFALFA is just the beginning,” Haynes said.
Several graduate students at Cornell will be basing their Ph.D. dissertations on the discoveries of ALFALFA made at Arecibo. Stierwalt hopes to focus on the cosmological implications found in the telescope’s data to study how large-scale structures such as galaxies clump together into certain formations. Kent will not only be studying the HI mass function but also helping to contribute ALFALFA’s information to the U.S. National Virtual Observatory, a comprehensive national database that will allow researchers to cross-reference not only ALFALFA’s findings but also astronomical data from other observatories as well.

The graduate students, Stierwalt said, will be traveling to Arecibo to conduct further research during spring break.

“We don’t have to worry about the weather, unlike optical astronomers,” Stierwalt said. “If it’s foggy or if it’s raining, we can still do our work.”

Both Prof. Robert Brown, astronomy, director of NIAC, and Prof. Riccardo Giovanelli, astronomy, are at Arecibo conducting the survey and were unable to comment.