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May 6, 2015 | by Stephen Luntz
The most distant, and therefore oldest, galaxy ever seen has had its distance confirmed. The discovery gives us our best opportunity yet to learn about galaxy building in the early universe.
Images from the Hubble and Spitzer space telescopes revealed Galaxy EGS-zs8-1 as being enormously redshifted, and therefore very, very distant. However, to confirm it as a record breaker required a larger, ground based instrument. This has now been done using one of Keck Observatory’s 10-meter telescopes, with the results published in The Astrophysical Journal.
Keck’s Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) measured EGS-zs8-1 at a z of 7.73, which translates to a distance of 13.0 billion light years. With the universe 13.7–13.8 billion years old, this means we are seeing back to when it was just 5% of its current age. Although this is the most distant confirmed galaxy, it does not quite match the Gamma Ray Burst GRB 090423 whose red shift was 8.2. There have been several observations of galaxies that at their maximum could be further away, but whose measurements have large margins for error.
The remarkable thing about EGS-zs8-1 is how evolved it was for the time. “It has already built more than 15% of the mass of our own Milky Way today,” said lead author Dr Pascal Oesch of Yale. “But it had only 670 million years to do so. The universe was still very young then.” At the point where we see it, EGS-zs8-1 is still in rapid star formation mode, 80 times the stately rate of the Milky Way.
The period where we see EGS-zs8-1 was an important one for the universe during what is known as the epoch of reionization. The light of the first stars split neutral hydrogen into an ionized plasma which absorbed much of the light, and making the universe opaque. As time went on the universe grew to the point where matter was sufficiently spread that light had a better chance of escaping without being absorbed by this plasma, giving us a chance to see it.
MOSFIRE, which started observations in 2012, enables astronomers to measure the redshift of several galaxies at once. The researchers also found two other galaxies they describe as “very similar sources” with red shifts of 7.21 and 7.51, indicating that EGS-zs8-1 is part of a continuum, rather than a strange outlier. The observations were clear enough to provide support for the theory that the first stars were massive giants, many larger than anything that exists today.
The paper notes that the discovery bodes well for measuring the distances to very early galaxies with the James Webb Space Telescope when it launches in 2018.
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