Using massive clusters of galaxies as "cosmic
telescopes," a research team led by a Johns Hopkins
University astronomer has found what may be infant galaxies
born in the first billion years after the beginning of the
universe.
If these findings are confirmed, the extra
magnification provided by these gargantuan natural
telescopes will have given astronomers their best-ever view
of galaxies as they formed in the early universe, more than
12 billion years ago, said Holland Ford, a professor in the
Henry A. Rowland
Department of Physics and Astronomy in the university's
Krieger School of Arts and Sciences. Ford is the head of
the Hubble Space
Telescope's Advanced Camera for Surveys Science Team,
which also includes researchers from the
Space Telescope Science
Institute, PUC in Chile and other universities around
the world.
Ford announced the team's results June 5 at the
American Astronomical Society meeting in Calgary, Alberta,
Canada. The team's spectroscopic observations were made
possible, he said, by gravitational lensing, the bending of
light caused by gravity's warping of space in the presence
of such massive objects as clusters of galaxies.
"One of Einstein's most startling predictions was that
a gravitation field can be thought of as a distortion of
space and time," Ford said. "Gravitational lensing by
massive clusters of galaxies that have about 1 million
billion times more mass than the sun provides one of the
most striking confirmations of Einstein's prediction."
Our view of distant galaxies behind a cluster can be
magnified by amounts that vary from barely detectable to as
many as 50 or 100 times normal size, depending on the
location of the galaxy and the distribution of mass within
the cluster, Ford said. The clusters are, in effect, giant
cosmic telescopes that allow astronomers to find and study
distant galaxies that otherwise would be too faint to
study.
"Astronomers want to know when the first galaxies
formed, how large and how bright galaxies are at birth and
how galaxies grow into large mature galaxies like our home
Milky Way galaxy," Ford said. "Our team is searching for
infant galaxies that are less than a billion years old by
comparing images of strongly lensing clusters taken by the
Hubble Space Telescope with images of the same clusters
taken by the Magellan, the Very Large Telescopes and Gemini
telescopes. The infant galaxies are so far away their light
is almost or entirely redshifted to wavelengths that cannot
be detected with Hubble's Advanced Camera for Surveys but
can be detected with infrared detectors on the world's
largest telescopes."
Using this technique, the ACS team has searched for
infant galaxies behind 14 lensing clusters. If longer
spectroscopic observations of the three brightest candidate
galaxies confirm that they are indeed in the early
universe, these galaxies will provide astronomers their
clearest view yet of the youngest galaxies ever seen.
The presentation was based on the AAS Abstract 66.03
"Bright Candidates of Galaxies at Redshift 7-8 in the ACS
Cluster Fields" by Wei Zheng, Ford and V. Motta, all of
Johns Hopkins; L. Infante, PUC, Chile; M. Postman, Space
Telescope Science Institute; and the ACS Science Team.
The results are based on observations collected at the
European Southern Observatory, Chile; the Las Campanas
Magellan Telescopes in Chile; and Gemini North, a telescope
operated by the Gemini Observatory/Association of
Universities for Research in Astronomy.
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