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"We show that gravitational lensing by foreground galaxies will lead to a higher number of galaxies to be counted at redshifts z>8-10. This number may be boosted significantly, by as much as an order of magnitude. If there existed only three galaxies above the detection threshold at redshifts z>10 in the Hubble field-of-view without the presence of lensing, the bias from gravitational lensing may make as many as 10-30 of them visible in the Hubble images," explains Windhorst. "In this sense, the very distant universe is like a house of mirrors that you visit at the State Fair -- there may be fewer direct lines-of-sight to a very distant object, and their images may reach us more often via a gravitationally-bent path. What you see is not what you've got!''
Future surveys will need to be designed to account for a significant gravitational lensing bias in high-redshift galaxy samples. Only the JWST -- if it gets finished as designed -- can ultimately make sense out of this gravitationally biased distant universe because it will have exquisite resolution and sensitivity at longer wavelengths to disentangle these very distant objects from the foreground lensing galaxies. This work is too hard to do with Hubble's Wide Field Camera 3 at redshifts z >= 10, because at Hubble's resolution one literally can no longer see the forest for the trees at these extreme distances.
"Our suggestion of the possibility of large gravitational lensing biases in high redshift samples is of crucial importance to the optimal design of surveys for the first galaxies
no·nil·lion /noʊˈnɪlyən/ Show Spelled
[noh-nil-yuhn] Show IPA
noun, plural -lions, ( as after a numeral ) -lion, adjective
1. a cardinal number represented in the U.S. by 1 followed by 30 zeros, and in Great Britain by 1 followed by 54 zeros.
2. amounting to one nonillion in number.
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1680–90; < F, equiv. to non- (< L nōnus ninth) + -illion, as in million million
no·nil·lionth, noun, adjective
An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the (base 10) exponent being applied to this amount (therefore, to be an order of magnitude greater is to be 10 times as large). Such differences in order of magnitude can be measured on the logarithmic scale in "decades" (i.e. factors of ten).
A gravitational lens not only distorts the image of a distant object, it can also act like an optical lens
A false-color image of a galaxy in the distant universe as seen by the Submillimeter Array (SMA). The four knots in the image are all the same galaxy; it appears multiple and distorted because of an intervening galaxy (not visible to the SMA) that magnifies and deforms it. Credit: M. Negrello et al.
A gravitational lens not only distorts the image of a distant object, it can also act like an optical lens, collecting and refocusing the light to make it appear brighter. Wondering if gravitational lensing might be responsible for the unusual brightness of these objects, the Herschel scientists teamed up with CfA astronomers Mark Gurwell and Ray Blundell to use the Submillimeter Array (SMA) to help resolve the question through its superb spatial resolution.
The Herschel Space Observatory, launched in May 2009, has a powerful new camera designed to image the heavens at very long infrared wavelengths; galaxies undergoing bursts of star formation appear bright at these wavelengths because their young stars heat dust which then radiates in the infrared. When Herschel scientists analyzed the first images from the new camera, they discovered many new galaxies -- and a handful of outstanding, bright ones.
The SMA found that indeed the bright objects were distorted images of distant galaxies. Optical follow-ups helped to solidify the conclusion
The two images illustrate the effect of gravitational lensing. A massive galaxy at the center of the right panel causes the images of the background galaxies (white spots) to be enlarged and brightened.(Image credit: Joerg Colberg, Ryan Scranton, Robert Lupton, SDSS