Science News - January 30, 2010

For today’s top stories, visit SN Today at www.sciencenews.org

the deepest infrared image of the universe ever recorded. Another Hubble camera had examined the same patch of sky, the Hubble Ultra Deep Field, five years earlier in visible light. This well-publicized image revealed many faint, faraway galaxies, but not the most remote galaxies, which can be seen only in infrared.

Ultraviolet and visible light emitted by the youthful stars in the earliest, most distant galaxies is shifted to much longer wavelengths — the infrared part of the spectrum — by the expansion of the universe. The more remote the galaxy, the greater the redshift.

In September, two teams, including Bouwens-Illingworth’s, reported finding galaxies with redshift values of 7 to 8, corresponding to an era about 700 million years after the Big Bang. Since then, five teams have posted some 15 papers online about those galaxies, which have been observed at two sets of wavelengths and so are on surer footing.

On January 5 in Washington, D.C., at the winter meeting of the American Astronomical Society, Illingworth reported

that these galaxies, which are teeming with newborn stars, are about 5 percent the size and 1 percent the mass of the Milky Way, according to observations with the Spitzer Space Telescope. These are the seed galaxies that merged to form giant galaxies like the Milky Way, he said.

In their paper at arXiv.org, the researchers estimate that the three even more distant galaxies imaged by the Wide Field Camera 3 have a redshift of about 10, which if confirmed would be the largest redshift ever measured. Another team, led by Rogier Windhorst of Arizona State University in Tempe, reported on arXiv.org finding a separate group of 20 galaxies at that redshift using the same data from the refurbished Hubble.

Illingworth and Bouwens note that because most of the candidate distant galaxies that were identified by the Windhorst team lie near known, bright galaxies, the team may have been

confused by stray light from these bright galaxies.

“Bouwens and company appear to have done a more careful job than Windhorst’s team,” Ellis comments.

Ellis and other astronomers have said it would be surprising if all 20 galaxies found by Windhorst and his collaborators are from the same early era, since the Ultra Deep Field encom-passes a narrow strip of sky.

Such a finding would indicate that the early universe had a surprisingly high density of these galaxies.

Windhorst now says that a further analysis indicates that perhaps 10 of his team’s galaxies may not turn out to be so very distant after all.

Although the race is on to find more-convincing examples of distant galaxies, it’s likely that none of the candidates at redshift 10 can be confirmed until the launch the James Webb Space Telescope, astronomers agree. s

7. 4 Candidate galaxy described in 2006

TOP: NASA, ESA, G. ILLINGWORTH, R. BOUWENS, THE HUDF09 TEAM; BACK STORY, FROM LEF T: NASA, J. BLAKESLEE/JHU; NEX T TWO: NASA, ESA, N. PIRZKAL/STSCI; NASA, ESA, B. MOBASHER/STSCI; NASA, ESA, R. BOUWENS, G. ILLINGWORTH/UC SANTA CRUZ

This galaxy, recorded with Hubble’s Wide Field Camera 3, may be one of the most distant known, with a redshift of 10.

Back Story | SEEING IN RED

Distant galaxies appear to be receding from Earth because of the universe’s expansion, which shifts their light toward the red end of the spectrum. Technically, a galaxy’s redshift, or z, is a measure of its velocity away from Earth, but astronomers also use it as a gauge of the universe’s age at the time the light was emitted. With data on the age of the universe and expansion rate, a measured redshift can be translated into a distance in light-years that indicates how long it took the galaxy’s light to travel to Earth. The table gives travel times for various redshifts based on an age for the universe of 13. 7 billion years and an expansion rate of 71 kilometers per second per megaparsec. The images show cosmic bodies with various redshifts.