CALTECH TEAM FINDS THE MOST DISTANT KNOWN GALAXIES




Figure 1
Fig. 1: 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.


TIFF version


Figure 2
Fig.2: A mosaic of six distant galaxies located by gravitational lensing. Each image, taken with the NIRSPEC instrument on Keck II, reveals a faint spectrum line (circled) in the infrared spectral region which the astronomers interpret as arising from a line of neutral hydrogen, significantly `redshifted' from its normal location in the ultraviolet. The team has invested significant amounts of observing time to eliminate the possibility that each faint line arises from a different atomic species, for example as would be the case if the galaxies were at less extreme distances.


Figure 3
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.



RELATED LINKS

ASTRONOMY MAGAZINE PODCAST:
http://www.astronomy.com/asy/default.aspx?c=a&id=5777

Richard Ellis's lecture at Waimea (Apr. 2006)
AUDIO: http://www.keckobservatory.org/podcast/ellis_06.mp3
SLIDES: http://www.keckobservatory.org/podcast/ellis_06.pdf







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