Four primordial galaxies less than 400 million years after the Big Bang, three of which are the most distant confirmed so far.
An international team of astronomers has discovered the oldest and most distant galaxies so far confirmed thanks to data from the James Webb Space Telescope (JWST). The telescope captured the light emitted by these galaxies more than 13.4 billion years ago, which means that the galaxies date back to less than 400 million years after the Big Bang, when the universe was only 2% of its size. current age.
Initial observations by JWST have revealed several galaxies at extreme distances, as have previous observations with the Hubble Space Telescope. Now, four of these targets have been confirmed by obtaining long spectroscopic observations, which not only provide confident measurements of their distances, but also allow astronomers to characterize the physical properties of galaxies.
“We discovered galaxies in a fantastically early time in the distant universe,” said Brant Robertson, a professor of astronomy and astrophysics at UC Santa Cruz. “With the James Webb Space Telescope, for the first time we can find galaxies that distant and then spectroscopically confirm that they are indeed that far away.”
Astronomers measure the distance to a galaxy by determining its redshift, the phenomenon by which light or other electromagnetic radiation emitted by a receding object has a longer wavelength than it did when it was emitted. This is equivalent to saying that in the case of light the color goes in the direction where red is. Due to the expansion of the universe, distant objects appear to be moving away from us and their light is stretched to longer and redder wavelengths by the Doppler effect. Photometric techniques based on images captured through various filters can provide redshift estimates, but definitive measurements require spectroscopy, which separates an object’s light into its wavelengths.
The new discoveries focus on four galaxies with redshifts greater than 10 . Two galaxies initially observed by Hubble now have confirmed redshifts of 10.38 and 11.58. The two most distant galaxies, both detected in the JWST images, have redshifts of 13.20 and 12.63 , making them the most distant galaxies confirmed by spectroscopy to date. A redshift of 13.2 corresponds to about 13.5 billion years ago.
Co-author Sandro Tacchella of the University of Cambridge in the UK added: ‘It is difficult to understand galaxies without understanding the initial periods of their development. As with humans, much of what happens next depends on the impact of these first generations of stars. Many questions about galaxies awaited Webb’s transformative opportunity, and we are excited to help unravel this story.”
Other teams have identified candidate galaxies at even higher redshifts based on photometric analyzes of JWST images, but these have yet to be confirmed by spectroscopy. The following papers on the new discoveries have been submitted for publication and are available online:
- Discovery and properties of the earliest galaxies with confirmed distances (arxiv.org)
- Spectroscopy of four metal-poor galaxies beyond redshift ten. (webbtelescope.org)