Astronomers report most distant known galaxies, discovered and confirmed – Zoo House News

Astronomers report most distant known galaxies, discovered and confirmed – Zoo House News

  • Science
  • December 11, 2022
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An international team of astronomers has discovered the earliest and most distant galaxies confirmed so far using data from the James Webb Space Telescope (JWST). The telescope captured the light emitted by these galaxies more than 13.4 billion years ago, meaning the galaxies date back less than 400 million years after the Big Bang, when the universe was only 2% of its current age.

Initial observations by JWST revealed several candidate galaxies at extreme distances, as did previous Hubble Space Telescope observations. Now four of these targets have been confirmed by long spectroscopic observations, which not only provide reliable measurements of their distances but also allow astronomers to characterize the galaxies’ physical properties.

“We have discovered galaxies at fantastically early times in the distant Universe,” said Brant Robertson, professor of astronomy and astrophysics at UC Santa Cruz. “With JWST, we can now, for the first time, find galaxies that far away and then confirm spectroscopically that they really are that far away.”

Astronomers measure the distance to a galaxy by determining its redshift. Due to the expansion of the universe, distant objects appear to be moving away from us and their light is stretched to longer, redder wavelengths by the Doppler effect. Photometric techniques based on images taken through various filters can provide redshift estimates, but definitive measurements require spectroscopy, which splits the light from an object into its wavelength components.

The new results focus on four galaxies with redshifts greater than 10. Two galaxies originally observed by Hubble now have confirmed redshifts of 10.38 and 11.58. The two most distant galaxies, both detected in 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.

“This is far beyond what we could have imagined before JWST,” said Robertson. “At redshift 13, the universe is only about 325 million years old.”

Robertson and Emma Curtis-Lake from the University of Hertfordshire (UK) will present the new results on December 12 at a conference of the Space Telescope Science Institute (STScI) in Baltimore on the topic “First Science Results from JWST”. They are the lead authors of two papers on the results that have not yet been peer-reviewed.

The observations result from a collaboration of scientists who led the development of two of the instruments on board Webb, the near-infrared camera (NIRCam) and the near-infrared spectrograph (NIRSpec). The study of the faintest and earliest galaxies was the main motivation behind the concepts for these instruments. In 2015, the instrument teams joined forces to propose the JWST Advanced Deep Extragalactic Survey (JADES), an ambitious program allocated just over a month of telescope time, designed to provide a view of the early Universe unprecedented at both depths and detailed. JADES is an international collaboration of more than eighty astronomers from ten countries.

“These results are the culmination of why the NIRCam and NIRSpec teams have joined forces to conduct this observing program,” said Marcia Rieke, principal investigator of NIRCam at the University of Arizona.

The JADES program began with NIRCam, using over 10 days of mission time to observe a small patch of sky in and around the Hubble Ultra Deep Field. Astronomers have been studying this region with almost every major telescope for over 20 years. The JADES team observed the field in nine different infrared wavelength ranges and captured exquisite images showing nearly 100,000 distant galaxies, each billions of light-years away.

The team then used the NIRSpec spectrograph for a single three-day observation period to collect light from 250 faint galaxies. This led to precise redshift measurements and revealed the properties of the gas and stars in these galaxies.

“With these measurements, we can know the intrinsic brightness of the galaxies and find out how many stars they have,” Robertson said. “Now we can start to really dissect how galaxies are assembled over time.”

Co-author Sandro Tacchella from the University of Cambridge in the UK added: “It is difficult to understand galaxies without understanding the early stages of their evolution. Much like humans, so much of what happens later depends on the impact of these early generations of galaxies on the stars. So many questions about galaxies have awaited Webb’s transformative opportunity, and we’re thrilled to play a part in unveiling this story.”

According to Robertson, star formation in these early galaxies would have started about 100 million years before the age at which they were observed, which would have pushed the formation of the earliest stars back to about 225 million years after the Big Bang.

“We’re seeing evidence of star formation about as early as we could expect based on our galaxy-forming models,” he said.

Other teams have identified candidate galaxies at even higher redshifts based on photometric analysis of JWST images, but these have yet to be confirmed by spectroscopy. JADES will continue in 2023 with a detailed survey of another field, focusing on the iconic Hubble Deep Field, and then returning to the Ultra Deep Field for another round of deep imaging and spectroscopy. Many other candidates in the field await spectroscopic investigations, with hundreds of hours of additional time already allocated.

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