* Astronomy

Discovery of a possibly old galaxy at z=6.027, multiply imaged by the massive cluster Abell 383

Astronomers have uncovered one of the youngest galaxies in the distant universe, with stars that formed 13.5 billion years ago, a mere 200 million years after the Big Bang. The finding addresses questions about when the first galaxies arose, and how the early universe evolved.
NASA's Hubble Space Telescope was the first to spot the newfound galaxy. Detailed observations from the W.M. Keck Observatory on Mauna Kea in Hawaii revealed the observed light dates to when the universe was only 950 million years old; the universe formed about 13.7 billion years ago.
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First galaxies were born much earlier than expected

Using the amplifying power of a cosmic gravitational lens, astronomers have discovered a distant galaxy whose stars were born unexpectedly early in cosmic history. This result sheds new light on the formation of the first galaxies, as well as on the early evolution of the Universe.

"We have discovered a distant galaxy that began forming stars just 200 million years after the Big Bang. This challenges theories of how soon galaxies formed and evolved in the first years of the Universe. It could even help solve the mystery of how the hydrogen fog that filled the early Universe was cleared" - Johan Richard, the lead author of a new study.

Richard's team spotted the galaxy in recent observations from the NASA/ESA Hubble Space Telescope, verified it with observations from the NASA Spitzer Space Telescope and measured its distance using W. M. Keck Observatory in Hawaii.

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Title: Discovery of an old galaxy at z=6.027, multiply imaged by the massive cluster Abell 383
Authors: Johan Richard (1,2), Jean-Paul Kneib (3), Harald Ebeling (4), Dan Stark (5), Eiichi Egami (6), Andrew K. Fiedler (6) ((1) CRAL/Lyon (2) Dark Cosmology Centre (3) LAM/OAMP (4) U.Hawaii (5) IoA, Cambdrige (6) Steward Observatory)

We report the discovery of an old z=6.027 galaxy, multiply imaged by the cluster Abell 383 and detected in new Hubble Space Telescope ACS and WFC3 imaging, as well as in Warm Spitzer observations. This galaxy was selected as a pair of i-dropouts; its suspected high redshift was confirmed by the measurement of a strong Lyman-alpha line in both images using Keck/DEIMOS. Combining Hubble and Spitzer photometry after correcting for contamination by line emission (estimated to be a small effect), we identify a strong Balmer break of 1.5 magnitudes, suggesting the presence of old stars from an early episode of star formation. Taking into account the magnification factor of 11.4±1.9 (2.65±0.17 mag) for the brightest image, the unlensed AB magnitude for the source is 27.2±0.05 in the H band and 25.7±0.08 at 3.6 um, corresponding to a 0.4 L* galaxy. The UV slope is consistent with beta~2.0, and from the rest-frame UV continuum we measure a current star formation rate of 2.4±1.1 Msol/yr. The unlensed half-light radius is measured to be 300 pc, from which we deduce a star-forming surface density of ~10 Msol/yr/kpc2. The Lyman-alpha emission is found to be extended over ~3 arcsec along the slit, corresponding to ~5 kpc in the source plane. This can be explained by the presence of a much larger envelope of neutral hydrogen around the star-forming region. Finally, fitting the spectral energy distribution using 7 photometric data points, we derive the following properties: an intrinsic stellar mass of M*=6.3+2.8 -1.2 10^9 Msol, an age of 640-940 Myrs (corresponding to a redshift of formation of 18±4, and very little reddening. The star-formation rate of this object was much stronger in the past than at the time of observation, suggesting that we may be missing a fraction of galaxies at z~6 which have already faded in rest-frame UV wavelengths.

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