Thursday, July 12, 2007

Astronomers Strain to Glimpse Oldest Galaxies Yet



Astronomers Strain to Glimpse Oldest Galaxies Yet

A high magnification scan of the heavens may have captured faint light from 13-billion-year-old galaxies

Astronomers say they have discovered a handful of relatively small galaxies that date to 500 million years after the big bang, or several hundred million years earlier than the previous oldest galaxies. The ancient objects may have initiated a key event called reionization that led to the clumping of small galaxies into larger ones.
Confirming the finding will take additional work, but if true, "it's scratching the edge of the universe," says astronomer Richard Ellis of the California Institute of Technology in Pasadena, who took part in the research. "We're really pushing out our telescopes to new limits to find these objects."

Ellis, his PhD student Dan Stark and their colleagues trained one of the world's biggest telescopes, the Keck 2 atop Hawaii's Mauna Kea, to scan light grazing massive clusters of closer galaxies [see image above], which focused the light coming from more ancient galaxies behind them and magnified it 20 times in a process called gravitational lensing.

These natural magnifying glasses revealed six points in the sky glowing feebly at telltale wavelengths of infrared light, according to the group's study published online in The Astrophysical Journal. Because the universe is expanding, light from distant sources is stretched from visible wavelengths to infrared, called redshifting, with the exact wavelength corresponding to the age of the object.

Ellis says the intensity of the light suggests that the galaxies are one hundredth or one thousandth the Milky Way's size, with a mass of up to 10 million suns, compared with our galaxy's 10 billion solar masses.

"This is the first credible example of redshift-10 galaxies"—corresponding to 500 million years after the big bang—"but it's not conclusive," says astrophysicist Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Nailing a galaxy's age requires precisely measuring its infrared intensity along a range of wavelengths, and for now the measurements are relatively crude, he adds.

Loeb says "cosmic dawn," when the first stars in the universe lit up, probably dates to 200 million years or sooner after the big bang. But the newly discovered objects may have kicked off the subsequent phase of reionization, in which ultraviolet starlight stripped electrons from hydrogen gas. Galaxies grew in size as a result, Loeb says, because reionized hydrogen would have been too hot to clump together unless present in more massive quantities.

The Caltech team estimates that the newly discovered galaxies' combined radiation would have been sufficient to break apart hydrogen atoms.


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This artist's concept shows a warm, watery alien world in the early universe whose sky is filled with a variety of galaxies. Spitzer data showed that the early universe was a big zoo with "animals" of all sorts, including surprisingly old, dead galaxies that stopped forming stars very quickly. Image courtesy David A. Aguilar (CfA).

Astronomical Surprise: Massive Old Galaxies Starve To Death In The Infant Universe

Science Daily — Pasadena, CA -- Astronomers have found distant red galaxiesvery massive and very oldin the universe when it was only 2.5 billion years post Big Bang. "Previous observations suggested that the universe at this age was home to young, small clumps of galaxies long before they merged into massive structures we see today," remarked Carnegie Observatories Ivo Labbé, who led the group of astronomers in the study.* "We are really amazedthese are the earliest, oldest galaxies found to date. Their existence was not predicted by theory and it pushes back the formation epoch of some of the most massive galaxies we see today."

About two years ago, astronomers from Leiden (The Netherlands) using the European ground-based Very Large Telescope found a population of distant red galaxies in the near infrared. But the images could not ascertain what made the galaxies red: Were they old and "dead" and no longer forming stars, or were massive amounts of dust obscuring star-forming regions?

The Labbé-led group used the infrared-imaging Spitzer Space Telescope to analyze the content of the new galactic population to address the questions of age, stellar mass, and activity. Giovanni Fazio (Harvard-Smithsonian Center for Astrophysics), a co-author on the study, said, "Spitzer offers capabilities that the Hubble Space Telescope and other instruments don't, giving us a unique way to study very distant galaxies long ago that eventually became the galaxies we see around us now."

The team was particularly surprised to find very old, red galaxies that had stopped forming new stars altogether. They had rapidly formed massive amounts of stars out of gas much earlier in the universe's history, but then suddenly starved to death, raising the question of what caused them to die so early. Such "red and dead" galaxies may be the forefathers of some of the old and giant elliptical galaxies seen in the local universe today.

In addition to the old "dead" galaxies long past star formation, there were other red, dusty galaxies still vigorously producing stars. Jiasheng Huang (Harvard-Smithsonian Center for Astrophysics) said, "We're detecting galaxies we never expected to find, having a wide range of properties we never expected to see." Apparently, the early universe was already a wildly complex place. "It's becoming more and more clear that the young universe was a big zoo with animals of all sorts," continued Labbé. "There's as much variety in the early universe as we see around us today."

Ultimately, these studies will help to unravel how galaxies like our Milky Way assembled and how they got to look the way they appear today. The research will be published in an upcoming issue of The Astrophysical Journal (Letters).

Carnegie Observatories: http://www.ociw.edu/

More information on Spitzer can be found at: http://www.spitzer.caltech.edu/spitzer/index.shtml

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* Researchers on the project were Ivo Labbé, Carnegie Observatories; Jiasheng Huang, Harvard-Smithsonian Center for Astrophysics; Marijn Franx, Leiden Observatory; Gregory Rudnick, NOAO; Pauline Barmby, Harvard-Smithsonian Center for Astrophysics, Emanuele Daddi, NOAO; Pieter G. van Dokkum, Yale University; Giovanni G. Fazio, Harvard-Smithsonian Center for Astrophysics; Natascha Forster Schreiber Max Plank-Institute für extraterrestrische Physik; Alan Moorwood, ESO; Hans-Walter Rix, Max-Plank-Institute für Astronomie; Huub Röttgering NOAO; Ignaciao Trujillo, Max-Plank-Institute für Astronomie; Paul van der Werf, Leiden Observatory.

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