The Galaxy Most Distant

Keck Gives a View into Space 15 Billion Light Years Away

by Robert Sanders

Berkeley astronomers have obtained images of the most distant known galaxy, an object 15 billion light years away formed when the universe was only one tenth its current age.

The image was captured by the world's largest telescope, the 10-meter Keck Telescope atop Mauna Kea in Hawaii, but is too faint to be observed in detail with most telescopes smaller than Keck.

Discovered in the radio region earlier this year by astronomers in England, the galaxy, called 8C 1435+63, has a redshift of 4.25. The previous most distant galaxy had a redshift of 3.8, although some quasars have been discovered with redshifts of 4.9.

The higher the redshift the farther away an object is, because distant objects are receding at ever increasing speeds as a result of the expansion of the universe. Receding objects have their light shifted to longer or redder wavelengths. At a redshift of 4.25 even short-wavelength blue light is shifted out of the visible into the near infrared region.

The Berkeley team, led by Hyron Spinrad, professor of astronomy, observed the galaxy using the low resolution imaging spectrometer and the near infrared camera mounted on the Keck Telescope. The detectors together provided not only an image but also spectra of the galaxy, which are used to measure redshift.

Spinrad's colleagues were James Graham, assistant professor of astronomy and one of the builders of the near infrared camera while at Caltech, and Arjun Dey, who just received his PhD in astronomy.

They reported their findings in the Jan. 1 Astrophysical Journal.

The galaxy is between 150,000 and 200,000 light years across--five times bigger than Andro-meda. What astronomers see is how the galaxy looked 15 billion years ago, Spinrad notes.

The most surprising aspect of their observations, Spinrad says, is that despite the relatively young age of the galaxy, it seems to have evolved significantly. It has some internal structure, which implies more maturity than its presumed age would suggest.

In addition, one end of the galaxy is red, implying either lots of old stars and thus an old galaxy, or lots of dust, Dey says. Future infrared observations with the Keck telescope should help them determine the age of the population of stars in the galaxy, and thus estimate when the galaxy formed.


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