A Young Cluster of Galaxies at z=2.5
Matthew A. Malkan, Harry Teplitz, and Ian S. McLean

FOR RELEASE 10:15 A.M. CDT, June 10, 1996

For More Information: Harlan Lebo (310) 206-0510 [harlanl@college.ucla.edu]

Matthew Malkan (310) 825-3404 [malkan@astro.ucla.edu]

Harry Teplitz is presenting these findings in Madison (608) 233-9717


UCLA astronomers, in the first successful application of a new technique to discover ``primeval'' galaxies, will today report their discovery of two clusters of infant galaxies, which are so distant that the light we are now receiving from them has been travelling for five-sixths of the entire history of the Universe.

With the Keck 10-meter telescope on Mauna Kea, Hawaii, they have detected the light from several large groupings of young stars seen when the Universe was only a few billion years old. It provides a view of galaxies like our own Milky Way in their first stages of formation, approximately 12.5 billion light years ago, so that the telescope is in effect a time machine.

``At last, we are not merely theorizing about how galaxies like ours are born and evolve into their current states. We are now actually watching this happen," said Matthew Malkan, a UCLA Professor of Physics and Astronomy. His colleagues are Ian McLean, UCLA Professor of Physics and Astronomy, and Harry Teplitz, a UCLA graduate student in Physics and Astronomy, who will present their latest findings today at a meeting of the American Astronomical Society in Madison, Wisconsin.

Until recently, the only objects known in these early stages of the Universe's 15-billion-year history had been the enigmatic quasars and the gaseous clouds in front of them which absorb a portion of their light. These objects are suspected to have some connection with normal galaxies like ours, but the relation is still unknown, Teplitz said. The key problem is that no stars can be detected in them. The formation of stars is the crucial process in galaxy evolution. It is necessary for the formation of planets, and the synthesis of heavy elements, and thus it is essential for the development of life.

The first actual detection of starlight from a newly formed galaxy was published last year by the same three UCLA researchers. McLean explained that until that time, extensive searches looking for visible-light had failed to discover any primeval galaxies. Instead, The UCLA project used an array of detectors sensitive infrared light (the radiation at wavelengths longer than the visible region of the electromagnetic spectrum). They used a special glass filter which transmits light only at a wavelength that is emitted by hydrogen, the simplest and most common atom. This hydrogen emission would normally be visible in the red region of the spectrum. However, due to the enormous distance to the galaxy, its light waves are stretched out by 3.5 times as they travel to Earth. So the hydrogen emission is "redshifted" to the infrared portion of the spectrum, where it was detected.

The UCLA astronomers compared two pictures of the same region of sky in the constellation of Ursa Major -- one that was tuned to the hydrogen emission, and one that was not. They found one faint fuzzy image of a galaxy that was relatively two and half times brighter in the first picture, indicating that it had strong emission from hydrogen gas. The two pictures are combined into one false color photo. Light from hydrogen emission is shown in red and other light in blue. With this color scheme, the primeval galaxy (designated MTM 095355+545428), in the middle of the left-hand side, stands out as being far redder than any of the other objects.

Malkan explained that the hydrogen gas is glowing so brightly because it is bombarded by intense ultraviolet (short wavelength light) radiation from a large number of massive hot stars. "Since the lives of these stars are relatively brief, we must be viewing them shortly after they were born," he said. The astronomers estimated that the galaxy was forming new stars at a rate of 100 times the mass of our sun per year. (For comparison, the present-day rate of star formation in our Milky Way has dropped to less that one solar mass each year).

In December 1995, the UCLA team was back at Keck to learn more about the stars in this infant galaxy and see just how galaxies like the Milky Way evolve. They used a reflection grating to spread the faint light of the galaxy into a rainbow spectrum. As they had hoped, this directly showed the distinctive fingerprint of ultraviolet light from a large number of young stars, powerful enough to light up the glowing hydrogen gas around them. In the visible spectrum of the galaxy, the astronomers detected dark absorption bands, which are produced in the atmospheres of hot stars. They also discovered two more young galaxies nearby that form the earliest galaxy cluster ever seen. These confirming and follow-up discoveries were recently accepted for publication this summer in the Astrophysical Journal Letters. The UCLA team agreed that this discovery was the best Christmas present they ever had.

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Last modified June 10, 1996