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A team of astronomers led by Takatoshi Shibuya (The GraduateUniversity for Advanced Studies, Japan), Dr. Nobunari Kashikawa(National Astronomical Observatory of Japan), Dr. Kazuaki Ota(Kyoto University), and Dr. Masanori Iye (National AstronomicalObservatory of Japan) has used the Subaru and Keck Telescopes todiscover the most distant galaxy ever found, SXDF-NB1006-2, at adistance of 12.91 billion light years from the Earth. This galaxy is slightly farther away than GN-108036, which SubaruTelescope discovered last year and was the most distant galaxydiscovered at the time (Note 1). In addition, the team's researchverified that the proportion of neutral hydrogen gas in the750-million-year-old early Universe was higher than it is today. These findings help us to understand the nature of the earlyUniverse during the "cosmic dawn", when the light of ancientcelestial objects and structures appeared from obscurity. Astronomers think that the our Universe began 13.7 billion yearsago at the Big Bang. The exteme temperature and density of thisfireball decreased rapidly as its volume increased. Hot cosmicplasma composed mainly of protons and electrons recombined to formneutral hydrogen atoms within 380,000 years after the Big Bang;this was the beginning of the cosmic "dark age." From then on, the gas continued to cool and fluctuated in density.About 200 to 500 million years after the Big Bang, the dense partsof neutral hydrogen clouds contracted under their own gravity, andthe first stars and galaxies formed. The radiation from this firstgeneration of stars started to heat and reionize the hydrogen innearby space, eventually leading to the reionization of the entireUniverse. This was the era of "cosmic reionization" (Figure 1) or the "cosmicdawn". The current team focused their research on identifying theexact epoch of the cosmic dawn in an effort to answer majorastronomical questions about the history of our Universe. How did the team design research to explore such an ancient,extremely distant time? Their first steps were to conduct a surveyof distant galaxies and measure their number and brightness.Because light from the distant Universe takes time to reach theEarth, identification of more distant galaxies allows astronomersto trace farther back in time and locate the epoch of the cosmicdawn. However, neutral hydrogen in intergalactic space dimmed the lightfrom galaxies before the cosmic dawn and made them more difficultto observe. Because the team needed to search a vast area forobjects in the far distant Universe (Note 2), they used the primefocus camera mounted on the Subaru Telescope (Suprime-Cam) fortheir initial surveys. Suprime-Cam captures images of objects in a wide field of view fromthe large, 8.2 m primary mirror of the Subaru Telescope and iswell-known for discovering faint, far distant galaxies and thenmeasuring the amount of neutral hydrogen in the early Universe(Note 3). The use of Suprime-Cam was even more compelling with the 2008installation of new detectors with a sensitivity about twice ashigh as their predecessors, particularly in the red wavelengths(Note 4). Armed with the most sensitive eyes in the world, the researcherscould carry out surveys for extremely distant galaxies (beyondredshift 7, where the majority of energy output from galaxies isdetected in red wavelengths). To fine-tune their survey even more,a team led by Dr. Iye constructed a new special filter named NB1006through which they could selectively identify the light of distantgalaxies at a redshift of nearly 7.3. The team used Suprime-Cam, complete with its new, highly sensitivedetectors, attached the NB1006 filter to observe two specificallydesignated regions of the sky for detailed study: the Subaru DeepField and the Subaru XMM-Newton Deep Survey Field. After a total of 37 hours in 7 nights of observations in these widefields, the team carefully processed the images they had obtained.Shibuya measured the color of 58,733 objects in the images andidentified four galaxy candidates at a redshift of 7.3. A carefulinvestigation of the brightness variation of the objects allowedthe team to narrow down the number of candidates to two. Then it was necessary for the team to make spectroscopicobservations to confirm the nature of these candidates. Theyobserved the two galaxy candidates with two spectrographs, theFaint Object Camera and Spectrograph (FOCAS) on the SubaruTelescope and the Deep Imaging Multi-Object Spectrograph (DEIMOS)on the Keck Telescope, and identified one candidate for which acharacteristic emission line of distant galaxies could be detected. The current team found that the proportion of neutral hydrogen wasincreasing in the far distant Universe. They concluded that about80 percent of the hydrogen gas in the ancient Universe, 12.91billion years ago at a redshift of 7.2, was neutral. In sum, this careful research plan and procedures, including theappropriate removal of contaminations that could lead to falseresults, resulted in the successful discovery and confirmation ofthe most distant galaxy ever discovered: SXDF-NB1006-2 (Figures 2and 3). In addition, the findings gave the team confidence thatthey were observing an object during the last phase of the cosmicdawn. Although finding just one galaxy at a critical epoch is exciting byitself, it is not a sufficient sample to characterize the entireepoch. Precise measurement of the number of galaxies during thecosmic dawn requires surveys of even wider fields. The scheduled 2012 installation of Subaru's new instrument, HyperSuprime-Cam (HSC) will allow researchers to observe a field of viewseven times greater than that of Suprime-Cam and opens the door toa huge galaxy sample beyond redshift 7. Observations with HSC aresteps in the direction of uncovering the dark periods of theUniverse and understanding the physical properties and formation ofthe first stars and galaxies. Shibuya summarized the team's future intent and hopes: "Byconducting an extremely wide HSC survey for distant galaxies beyondredshift seven, we will find the mechanisms of the cosmicreionization in a variety of ways, not just by investigating theirnumber and brightness." Dr. Iye, the leader of the Thirty Meter Telescope (TMT) project atthe National Astronomical Observatory of Japan (NAOJ), added, "Wehave been pushing the limits of 8-10 m class telescopes to detectdistant galaxies. The 30 m mirror of the TMT will be able to gatherup to ten times more light than current large telescopes and detectfaint light from galaxies up to a redshift of 14. The day is not sofar off when the mysteries of the dark ages of the Universe and thephysical properties of the first galaxies will be revealed." These results will be published in the June 20, 2012, edition ofthe Astrophysical Journal. This research was supported by The JapanSociety for the Promotion of Science through Grant-in-Aid forScientific Research 23340050 and 19104004. We are high quality suppliers, our products such as SKYBOX HD Satellite Receiver Manufacturer , Twin Tuner Satellite Receiver for oversee buyer. To know more, please visits DVB-S2 Satellite Receiver.
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