Hubble Frontier Fields view of MACSJ0416.1–2403 Credit: NASA, ESA and the HST Frontier Fields team (STScI)
Observations have taken advantage of gravitational lensing to reveal the largest sample of the faintest and earliest known galaxies in the Universe. Some of these galaxies formed just 600 million years after the Big Bang and are fainter than any other galaxy yet uncovered by Hubble. The team has determined, for the 1st time that these small galaxies were vital to creating the Universe that we see today.
Hakim Atek’s team has discovered >250 tiny galaxies that existed only 600-900 million years after the Big Bang,one of the largest samples of dwarf galaxies yet to be discovered at these epochs. The light from these galaxies took >12 billion years to reach the telescope, allowing the astronomers to look back in time when the universe was still very young.
The accumulated light emitted by these galaxies could have played a major role in one of the most mysterious periods of the Universe’s early history – the epoch of reionisation which started when the thick fog of H2 that cloaked the early Universe began to clear. UV light was now able to travel over larger distances without being blocked and the Universe became transparent to ultraviolet light.
By observing UV light from the galaxies found in this study the astronomers were able to calculate whether these were in fact some of the galaxies involved in the process. The team determined, for the first time with some confidence, that the smallest and most abundant of the galaxies in the study could be the major actors in keeping the Universe transparent. By doing so, they have established that the epoch of reionisation – which ends at the point when the Universe is fully transparent – came to a close about 700 million years after the Big Bang.
“If we took into account only the contributions from bright and massive galaxies, we found that these were insufficient to reionise the Universe. We also needed to add in the contribution of a more abundant population of faint dwarf galaxies.”
To make these discoveries, the team utilised the deepest images of gravitational lensing made so far in 3 galaxy clusters, which were taken as part of the Hubble Frontier Fields programme. “Clusters in the Frontier Fields act as powerful natural telescopes and unveil these faint dwarf galaxies that would otherwise be invisible.” http://www.spacetelescope.org/news/heic1523/
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