The light from these four galaxies has taken more than 13.4 billion years to reach us, as they date back to less than 400 million years after the Big Bang, when the Universe was only 2% of its current age.
Distant galaxies selected and confirmed by the JWST JADES program. Image credit: Robertson et al., arXiv: 2212.04480.
Astronomers measure the distance to a galaxy by determining its redshift.
Due to the expansion of the Universe, distant objects appear to be receding from us and their light is stretched to longer, redder wavelengths by the Doppler effect.
Photometric techniques based on images captured through different filters can provide redshift estimates, but definitive measurements require spectroscopy, which separates the light from an object into its component wavelengths.
The new findings focus on four galaxies — dubbed JADES-GS-z10-0, JADES-GS-z11-0, JADES-GS-z12-0, and JADES-GS-z13-0 — with redshifts higher than 10.
The two first galaxies, initially observed by Hubble, now have confirmed redshifts of 10.38 and 11.58.
The two most distant galaxies, both detected in Webb images, have redshifts of 13.2 (corresponds to about 13.5 billion years ago) and 12.63, making them the most distant galaxies confirmed by spectroscopy to date.
“It was crucial to prove that these galaxies do, indeed, inhabit the early Universe,” said University of Hertfordshire astronomer Emma Curtis-Lake.
“It’s very possible for closer galaxies to masquerade as very distant galaxies.”
“Seeing the spectrum revealed as we hoped, confirming these galaxies as being at the true edge of our view, some further away than Hubble could see! It is a tremendously exciting achievement for the mission.”
“We’ve discovered galaxies at fantastically early times in the distant Universe,” said University of California, Santa Cruz’s Professor Brant Robertson.
“With Webb, for the first time we can now find such distant galaxies and then confirm spectroscopically that they really are that far away.”
“These are well beyond what we could have imagined finding before Webb. At redshift 13, the Universe is only about 325 million years old.”
The observations are part of the JWST Advanced Deep Extragalactic Survey (JADES), an ambitious program that has been allocated just over one month of Webb’s time and is designed to provide a view of the early Universe unprecedented in both depth and detail.
They were made using Webb’s Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrograph (NIRSpec) instruments.
“With these measurements, we can know the intrinsic brightness of the galaxies and figure out how many stars they have,” Professor Robertson said.
“Now we can start to really pick apart how galaxies are put together over time.”
“It is hard to understand galaxies without understanding the initial periods of their development,” added University of Cambridge astronomer Sandro Tacchella.
“Much as with humans, so much of what happens later depends on the impact of these early generations of stars.”
“So many questions about galaxies have been waiting for the transformative opportunity of Webb, and we’re thrilled to be able to play a part in revealing this story.”
“Star formation in these early galaxies would have begun about 100 million years earlier than the age at which they were observed, pushing the formation of the earliest stars back to around 225 million years after the Big Bang,” Professor Robertson said.
“We are seeing evidence of star formation about as early as we could expect based on our models of galaxy formation.”
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B.E. Robertson et al. 2022. Discovery and properties of the earliest galaxies with confirmed distances. arXiv: 2212.04480
Emma Curtis-Lake et al. 2022. Spectroscopy of four metal-poor galaxies beyond redshift 10. arXiv: 2212.04568
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