Z-Spec on the CSO Revealed Primeval
Galaxies
Tucked Behind Gravitational Lenses Caused By Foreground Galaxies 
Astronomers estimate that
half of the star formation in the universe is obscured by dust—making
many distant galaxies in the peak of their star-forming years
essentially invisible. But now the invisible has been revealed, thanks
to new instruments that can observe in the millimeter, submillimeter,
and far-infrared wavelengths in which these galaxies shine. In the
November 5 issue of Science, astronomers announce their discovery of
five distant, dust-obscured galaxies, magnified by cosmic
lenses—galaxies that bend light from a more distant source.
The astronomers noticed the galaxies in images returned by the
Herschel Space Observatory, a European Space Agency telescope launched
in 2009 to probe the universe in far-infrared and submillimeter
wavelengths. Caltech and JPL researchers helped develop Herschel's
instruments.
It was a novel Caltech and JPL–designed spectrometer called
Z-Spec, on the Caltech Submillimeter
Observatory, that revealed the
primeval galaxies tucked behind the lenses. Optical telescopes
following up on the Herschel data saw only the foreground lensing
galaxies.
Z-Spec, which has a
bandwidth 10 times bigger than that of other
spectrometers for these wavelengths, was able to measure redshifts for
four of the five galaxies—the first demonstration that a
millimeter-wave spectrometer can consistently provide redshifts for
distant galaxies—and confirmed that the light originated when the
universe was only two- to four-billion-years old. Z-Spec uses a unique
"2-dimensional" spectrometer to realize its large bandwidth while
keeping the instrument compact, and is a prototype for an even more
capable spectrometer planned for observations in space on the Japanese
SPICA far-infrared telescope.
Kathy Svitil
ksvitil@caltech.edu
The results are to be published in the
November 5th issue of Science entitled "The Detection of a
Population of Submillimeter-Bright, Strongly Lensed Galaxies" (Mattia
Negrello et al. 2010).
Caltech's press release
on Caltech's web site
JPL's
press release
Figure 1: Distortions of a Distant Galaxy
This diagram illustrates a cosmic phenomenon known as gravitational
lensing, in which a galaxy magnifies a second, more distant galaxy,
making it appear brighter and easier to study. The Herschel Space
Observatory turns out to be particularly good at spotting these distant
"lensed" galaxies. It has discovered five new ones, and is expected to
find many more.
In the diagram, the Herschel telescope and Earth are shown to the
right. A foreground galaxy is shown in blue, located approximately
three billion light-years away (its light took three billion years to
reach us). A more distant galaxy, about 11 billion light-years away, is
shown in red. The gravity of the foreground galaxy bends the light from
the distant one, as shown with the red lines. The pink lines show what
we actually see -- a distorted and magnified view of the distant
galaxy. An example of a final image taken by ground-based telescopes is
at the far left.
Herschel is a European Space Agency cornerstone mission, with science
instruments provided by consortia of European institutes and with
important participation by NASA. NASA's Herschel Project Office is
based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL
contributed mission-enabling technology for two of Herschel's three
science instruments. The NASA Herschel Science Center, part of the
Infrared Processing and Analysis Center at the California Institute of
Technology in Pasadena, supports the United States astronomical
community. Caltech manages JPL for NASA.
Image credit: NASA/JPL-Caltech
Figure 2: Caltech Submillimeter Observatory at the summit of the
mountain Mauna Kea, Hawai'i. The photo is linked from a
web page at Caltech Today.
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