Gravitational Lenses Helped to Find Most Distant Galaxies

Caltech astronomers have pioneered the use of foreground clusters of galaxies as `natural telescopes' to boost faint signals from the most distant sources, seen as they were when the Universe was only a few percent of its current age [Image Courtesy: Caltech Media Center. For more images and description of techniques, visit Johan Richard's page]

Today, at the "From IRAS to Herschel and Planck" conference at the Geological Society in London, Richard Ellis, Professor of Astronomy at the California Institute of Technology presented images of some faint and distant objects in his talk. These are the first traces of a population of the most distant galaxies yet seen - the light we see from them today left more than 13 billion years ago, when the universe was just 500 million years old or less than 4% of its present age. Using natural "gravitational lenses," an international team of astronomers that Prof. Ellis led, have found images of these galaxies using the 10-meter Keck II telescope, sited atop Mauna Kea on the Big Island of Hawaii. This new survey is the culmination of three years' painstaking observations.

When light from very distant bodies passes through the gravitational field of much nearer massive objects, it bends in an effect known as "gravitational lensing". This is one of the predictions of Albert Einstein's General Theory of Relativity. Massive clusters of galaxies are the best example of natural gravitational lenses. Using a pioneering technique in a series of campaigns, the group used the presence of such clusters to locate progressively more distant systems that would not be detected in normal surveys.

It is thought that when the universe was 300,000 years old, it entered a period when no stars were shining. Cosmologists refer to this phase of cosmic history as the "Dark Ages." Pinpointing the moment of "cosmic dawn" when the first stars and galaxies began to shine and the Dark Ages ended is a major observational quest and provides the motivation for building future powerful telescopes such as the Thirty Meter Telescope, and the space-borne James Webb Telescope.

Reference:
"A Keck Survey for Gravitationally Lensed Lyman-alpha Emitters in the Redshift Range 8.5<z<10.4: New Constraints on the Contribution of Low Luminosity Sources to Cosmic Reionization"
Daniel P. Stark, Richard S. Ellis, Johan Richard, Jean-Paul Kneib, Graham P. Smith, Michael R. Santos
The Astrophysical Journal, V.663, p.10 (July, 2007). Link to Abstract