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Caltech News Release
Embargoed for Release at 11 a.m. PDT, Wednesday, April 16, 2003
April 16, 2003

Astronomers find new evidence about universe's heaviest phase of star
formation

Contact: Robert Tindol
(626) 395-3631

PASADENA, Calif.  -- New distance measurements from faraway galaxies 
further strengthen the view that the strongest burst of star 
formation in the universe occurred about two billion years after the 
Big Bang.

Reporting in the April 17 issue of the journal Nature, California 
Institute of Technology astronomers Scott Chapman and Andrew Blain, 
along with their United Kingdom colleagues Ian Smail and Rob Ivison, 
provide the redshifts of 10 extremely distant galaxies which strongly 
suggest that the most luminous galaxies ever detected were produced 
over a rather short period of time.  Astronomers have long known that 
certain galaxies can be seen about a billion years after the Big 
Bang, but a relatively recent discovery of a type of extremely 
luminous galaxy -- one that is very faint in visible light, but much 
brighter
at longer wavelengths -- is the key to the new results.

This type of galaxy was first found in 1997 using a new and much more 
sensitive camera for observing at submillimeter wavelengths (longer 
than the wavelengths of visible light that allows us to see, but 
somewhat shorter than radio waves).  The camera was attached to the 
James Clerk Maxwell Telescope (JCMT), on Mauna Kea in Hawaii.

Submillimeter radiation is produced by warm galactic "dust" -- 
micron-sized solid particles similar to diesel soot that are 
interspersed between the stars in galaxies.  Based on their unusual 
spectra, experts have thought it possible that these "submillimeter 
galaxies" could be found even closer in time to the Big Bang.

Because the JCMT cannot see details of the sky that are as fine as 
details seen by telescopes operating at visible and radio 
wavelengths, and because the submillimeter galaxies are very faint, 
researchers have had a hard time determining the precise locations of 
the submillimeter galaxies and measuring their distances. Without an 
accurate distance, it is difficult to tell how much energy such 
galaxies produce; and with no idea of how powerful they are, it is 
uncertain how important such galaxies are in the universe.

The new results combine the work of several instruments, including 
the Very Large Array in New Mexico (the world's most sensitive radio 
telescope), and one of the 10-meter telescopes at the W. M. Keck 
Observatory on Mauna Kea, which are the world's largest optical 
telescopes.  These instruments first pinpointed the position of the 
submillimeter galaxies, and then measured their distances.  Today's 
article in Nature reports the first 10 distances obtained.

The Keck telescope found the faint spectral signature of radiation 
that is emitted, at a single ultraviolet wavelength of 0.1215 
micrometers, by hydrogen gas excited by either a large number of hot, 
young stars or by the energy released as matter spirals into a black 
hole at the core of a galaxy.  The radiation is detected at a longer, 
redder wavelength, having been Doppler shifted by the rapid expansion 
of the universe while the light has been traveling to Earth.

All 10 of the submillimeter galaxies that were detected emitted the 
light that we see today when the universe was less than half its 
present age.  The most distant produced its light only two billion 
years after the Big Bang (12 billion years ago). Thus, the 
submillimeter
galaxies are now confirmed to be the most luminous type of galaxies 
in the universe, several hundred times more luminous than our Milky 
Way, and 10 trillion times more luminous than the sun.

It is likely that the formation of such extreme objects had to wait 
for a certain size of a galaxy to grow from an initially almost 
uniform universe and to become enriched with carbon, silicon, and 
oxygen from the first stars.  The time when the submillimeter 
galaxies shone brightly can also provide information about how the 
sizes and makeup of galaxies
developed at earlier times.

By detecting these galaxies, the Caltech astronomers have provided an 
accurate census of the most extreme galaxies in the universe at the 
peak of their activity and witnessed the most dramatic period of star 
buildup yet seen in the Milky Way and nearby galaxies.  Now that 
their distances are known accurately, other measurements can be made 
to investigate the details of their power source, and to find out 
what galaxies will result when their intense bursts of activity come 
to an end.

For Interviews: 

Scott Chapman, schapman{at}submm.caltech.edu, (626) 395-4306
Andrew Blain, awb{at}astro.caltech.edu, (626) 395-4726

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