MACS1423-z7p64, a ‘Special’ Average Galaxy in the Distant Universe
MACS1423-z7p64 is an ultra-faint galaxy at a redshift of 7.6, that puts it about 13.1 billion years in the past. (The farther away an object is, the farther its light is shifted into the red end of the spectrum, due to the expansion of the universe.)
Astronomers- led by a graduate student at the University of California, Davis-
have discovered this galaxy, one of the most distant galaxies in the universe, and it’s nothing out of the ordinary.
Hence, what is so special about this one?
These ultradistant galaxies, seen as they were close to the beginning of the universe, are interesting to scientists because they fall within the “Epoch of Reionization,” a period about a billion years after the Big Bang when the universe became transparent.
After the Big Bang, the universe was a cloud of cold, atomic hydrogen, which blocks light. The first stars and galaxies condensed out of the cloud and started to emit light and ionizing radiation. This radiation melted away the atomic hydrogen like a hot sun clearing fog, and the first galaxies spread their light through the universe.
To find such faint, distant objects like MACS1423-z7p64, the astronomers took advantage of a giant lens in the sky.
As light passes by a massive object such as a galaxy cluster, its path gets bent by gravity, just as light gets bent passing through a lens. When the object is big enough, it can act as a lens that magnifies the image of objects behind it.
Scientists are surveying the sky around massive galaxy clusters that are the right size and distance away to focus light from very distant galaxies. While it is similar to millions of other galaxies of its time, z7p64 just happened to fall into the “sweet spot” behind a giant galaxy cluster that magnified its brightness tenfold and made it visible to the team, using the Hubble Space Telescope. They were then able to confirm its distance by analyzing its spectrum with the Keck Observatory telescopes in Hawaii.
► The study “Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization”, published in _Nature Astronomy _>> https://www.nature.com/articles/s41550-017-0091
► Read the preprint vesrion of this study on arXiv>> https://arxiv.org/abs/1704.02970
► Image explanation: Astronomers used the gravity of a massive galaxy cluster as a lens to spot an incredibly distant galaxy, about 13.1 billion years in the past. They used the Hubble Space Telescope to find the galaxy and confirmed its age and distance with instruments at the Keck Observatory in Hawaii.
Image credit: NASA/Keck/Austin Hoag/Marusa Bradac