CALTECH TEAM FINDS THE MOST DISTANT KNOWN GALAXIES
How gravitational lensing works: 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. Typical
magnification factors are 20 times, thereby bringing into view young
galaxies that would otherwise be unobservable. This technique has allowed
the Caltech astronomers to locate a new population of early feeble
sources which may be sufficiently numerous to be responsible for drawing
the so-called `Dark Ages' to a close.
A mosaic of six distant galaxies located by gravitational lensing.
image, taken with the NIRSPEC instrument on Keck II, reveals a faint spectrum line (circled) in the infrared spectral
the astronomers interpret as arising from a line of neutral hydrogen,
`redshifted' from its normal location in the ultraviolet. The team has
significant amounts of observing time to eliminate the possibility that each
faint line arises from a different atomic species, for example as would be
case if the galaxies were at less extreme distances.
Fig. 3: A selection of Hubble Space Telescope images of the cluster fields
with the newly-located sources marked. In total 9 clusters were searched
for early sources and 6 were found in the fields of three. Each foreground
cluster of galaxies acts as a natural telescope and the magnification is
predicted to be particularly strong along `critical lines' (marked as black
curves). The Caltech team used the Keck infrared spectrograph to search
specifically along these regions.
ASTRONOMY MAGAZINE PODCAST:
Richard Ellis's lecture at Waimea (Apr. 2006)
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