Keck Telescope and 'Cosmic Lens' Resolve Nature and Fate of Early Star-Forming Galaxy

Caltech News Release
For Immediate Release
October 8, 2008

Keck Telescope and "Cosmic Lens" Resolve Nature and Fate of Early
Star-Forming Galaxy

The combination demonstrates the eventual power of the Thirty Meter
Telescope

PASADENA, Calif.--Astronomers at the California Institute of
Technology (Caltech) and their colleagues have provided unique
insight into the nature of a young star-forming galaxy as it appeared
only two billion years after the Big Bang and determined how the
galaxy may eventually evolve to become a system like our own Milky
Way.

The team made their observations by coupling two techniques,
gravitational lensing--which makes use of an effect first predicted
by Albert Einstein in which the gravitational field of massive
objects, such as foreground galaxies, bends light rays from objects
located a distance behind, thus magnifying the appearance of distant
sources--and laser-assisted guide star (LGS) adaptive optics (AO) on
the 10-meter Keck Telescope in Hawaii. Adaptive optics corrects the
blurring effects of Earth's atmosphere by real-time monitoring of the
signal from a natural guide star or an artificial guide star.
Gravitational lensing enlarged the distant galaxy in angular size by
a factor of about 8 in each direction. Together with the enhanced
resolution using adaptive optics, this allowed the team to determine
the internal velocity structure of the remote galaxy, located 11
billion light-years from Earth, and hence its likely future evolution.

The researchers found that the distant galaxy, which is typical in
many respects to others at that epoch, shows clear signs of orderly
rotation. The finding, in association with observations conducted at
millimeter wavelengths, which are sensitive to cold molecular gas (an
indicator of galactic rotation), suggests that the source is in the
early stages of assembling a spiral disk with a central nucleus
similar to those seen in spiral galaxies at the present day.

Using the Hubble Space Telescope, the team located a distinctive
galaxy dubbed the "Cosmic Eye" because its form is distorted into a
ring-shaped structure by the gravitational field of a foreground
galaxy.

"Gravity has effectively provided us with an additional zoom lens,
enabling us to study this distant galaxy on scales approaching only a
few hundred light-years. This is 10 times finer sampling than
hitherto possible," explains postdoctoral research scholar Dan Stark
of Caltech, the leader of the study. "As a result, we can see, for
the first time, that a typical-sized young galaxy is spinning and
slowly evolving into a spiral galaxy much like our own Milky Way," he
says.

The research, described in the October 9 issue of the journal Nature,
provides a demonstration of the likely power of the future Thirty
Meter Telescope (TMT), the first of a new generation of large
telescopes designed to exploit AO.

When completed in the latter half of the next decade, TMT's large
aperture and improved optics will produce images with an angular
resolution three times better than the 10-meter Keck and 12 times
better than the Hubble Space Telescope, at similar wavelengths.
Because of the significant improvement in angular resolution provided
by AO, the TMT will be able to study the internal properties of small
distant galaxies, seen as they were when the universe was young.

Likewise, the Atacama Large Millimeter Array (ALMA), a large
interferometer being completed in Chile, will provide a major step
forward in mapping the extremely faint emission from cold hydrogen
gas--the principal component of young, distant galaxies and a clear
marker of cold molecular gas--compared to the coarser capabilities of
present facilities. In their recent research, the Caltech-led team
has provided a glimpse of what can be done with the superior
performance expected of TMT and ALMA.

The key spectroscopic observations were made with the OSIRIS
instrument, developed specifically for the Keck AO system by
astrophysicist James Larkin and collaborators at the University of
California, Los Angeles. Stark and his coworkers used the OSIRIS
instrument to map the velocity across the source in fine detail,
allowing them to demonstrate that it has a primitive rotating disk.

To aid in their analysis, the researchers combined data from the Keck
Observatory with data taken at millimeter wavelengths by the Plateau
de Bure Interferometer (PdBI), located in the French Alps. This PdBI
instrument is sensitive to the distribution of cold gas that has yet
to collapse to form stars. These observations give a hint of what
will soon be routine with the ALMA interferometer.

"Remarkably, the cold gas traced by our millimeter observations
shares the rotation shown by the young stars seen in the Keck
observations. The distribution of gas seen with our amazing
resolution indicates we are witnessing the gradual buildup of a
spiral disk with a central nuclear component," explains
coinvestigator Mark Swinbank of Durham University, who was involved
in both the Keck and PdBI observations.

This work demonstrates how important angular resolution has become in
ensuring progress in extragalactic astronomy. This will be the key
gain of both the TMT and ALMA facilities.

"For decades, astronomers were content to build bigger telescopes,
arguing that light-gathering power was the primary measure of a
telescope's ability," explains Richard S. Ellis, Steele Family
Professor of Astronomy at Caltech, a coauthor on the Nature study,
and a member of the TMT board of directors. "However, adaptive optics
and interferometry are now providing ground-based astronomers with
the additional gain of angular resolution. The combination of a large
aperture and exquisite resolution is very effective for studying the
internal properties of distant and faint sources seen as they were
when the universe was young. This is the exciting future we can
expect with TMT and ALMA, and, thanks to the magnification of a
gravitational lens, we have an early demonstration here in this
study," he says.

Coauthors on the paper, "The formation and assembly of a typical
star-forming galaxies at redshift z~3," are Simon Dye of Cardiff
University in Cardiff, Wales; Ian R. Smail of Durham University in
Durham, England; and Johan Richard of Caltech.

The W. M. Keck Observatory operates twin 10-meter telescopes located
on the summit of Mauna Kea. The observatory, made possible by grants
from the W. M. Keck Foundation totaling over $138 million, is managed
as a nonprofit corporation whose board of directors includes
representatives from Caltech and the University of California.

The Thirty Meter Telescope is currently in a detailed design and
development phase and represents a collaboration between Caltech, the
University of California, and the Association for Canadian
Universities Research in Astronomy. It has received generous support
from the Gordon and Betty Moore Foundation.

Further information on the Thirty Meter Telescope is available at
http://www.tmt.org.

Information on the Atacama Large Millimeter Array is available at
http://www.alma.nrao.edu.

Further information on the Keck telescopes, their adaptive optics
systems, and the OSIRIS instrument are available at:
https://www.keckobservatory.org/.

###

Contact:
Richard S. Ellis,
(626) 395-2598,
rse@xxxxxxxxxxxxxxxxx;

Kathy Svitil,
(626) 395-8022,
ksvitil@xxxxxxxxxxxx

.

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