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Webb Telescope Discovers and Verifies Known Galaxies at a Distance

Using information from the James Webb Space Telescope (JWAT), an international team of astronomers has found the earliest and most distant galaxies confirmed to date. These galaxies date back to less than 400 million years after the Big Bang, when the universe was only 2% of its present age, as the telescope captured light emitted by them more than 13.4 billion years ago.

The JWST Advanced Deep Extragalactic Survey (JADES) focused on the area in and around the Hubble Space Telescope’s Ultra Deep Field. Using Webb’s NIRCam instrument, scientists observed the field in nine different infrared wavelength ranges. From these images, the team searched for faint galaxies that are visible in the infrared but whose spectra abruptly cut off at a critical wavelength known as the Lyman break. Webb’s NIRSpec instrument then yielded a precise measurement of each galaxy’s redshift. Four of the galaxies studied (insets) date back to less than 400 million years after the big bang, when the universe was only 2% of its current age. Image Credit: NASA, ESA, CSA, M. Zamani (ESA/Webb), Leah Hustak (STScI); Science Credits: Brant Robertson (UC Santa Cruz), S. Tacchella (Cambridge), E. Curtis-Lake (UOH), S. Carniani (Scuola Normale Superiore), JADES Collaboration

Similar to earlier Hubble Space Telescope observations, the first JWST observations revealed several candidate galaxies at vast distances. Four of these targets have now been verified by long spectroscopic observations, which not only provide accurate distance measurements but also enable astronomers to describe the physical characteristics of the galaxies.

We have discovered galaxies at fantastically early times in the distant universe. With JWST, for the first time we can now find such distant galaxies and then confirm spectroscopically that they really are that far away.

Brant Robertson, Professor, Astronomy and Astrophysics, University of California Santa Cruz

By calculating a galaxy’s redshift, astronomers can determine its distance. The universe appears to be expanding away from the earth, and the Doppler effect causes distant objects’ light to be stretched to longer, redder wavelengths.

Redshift estimates can be obtained using photometric methods based on images acquired through various filters, but accurate measurements demand spectroscopy, which breaks down an object’s light into its constituent wavelengths.

The new discoveries concentrate on four galaxies that have redshifts higher than 10. Hubble’s initial observations of two galaxies have been confirmed to have redshifts of 10.38 and 11.58.

With redshifts of 13.20 and 12.63, the two most distant galaxies—both of which were found in JWST images—are the ones whose distance has been confirmed by spectroscopy to date. Redshift 13.2 indicates a time period of roughly 13.5 billion years ago.

Robertson added, “These are well beyond what we could have imagined finding before JWST. At redshift 13, the universe is only about 325 million years old.

The new findings will be presented on December 12th, 2022 at a Space Telescope Science Institute (STScI) conference in Baltimore titled “First Science Results from JWST.”

Robertson and Emma Curtis-Lake from the University of Hertfordshire (UK) will be making the presentation. They are the lead authors of two papers that discuss the findings but have not yet undergone peer review.

The Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrograph (NIRSpec), two of the instruments onboard Webb, were developed by scientists who worked together to produce the observations.

The primary inspiration behind the design of these instruments was the study of the faintest and oldest galaxies. The JWST Advanced Deep Extragalactic Survey (JADES), an ambitious program that has been allotted just over one month of the telescope’s time and is intended to provide an unprecedented view of the early universe in depth and detail, was proposed by the instrument teams in 2015.

More than 80 astronomers from ten different countries are part of the international collaboration known as JADES.

These results are the culmination of why the NIRCam and NIRSpec teams joined together to execute this observing program.

Marcia Rieke, NIRCam Principal Investigator, University of Arizona

A small area of sky in and around the Hubble Ultra Deep Field was observed using more than ten days of mission time by NIRCam, the first component of the JADES program. Over the past 20 years, nearly all of the large telescopes have been used by astronomers to study this region.

The JADES team studied the field using nine different infrared wavelength ranges, resulting in stunning images that show nearly 100,000 far-off galaxies, each billion of light years away.

The team then collected the light from 250 faint galaxies over the course of a single, three-day observation period using the NIRSpec spectrograph. The characteristics of the gas and stars in these galaxies were revealed and precise redshift measurements were obtained.

With these measurements, we can know the intrinsic brightness of the galaxies and figure out how many stars they have. Now we can start to really pick apart how galaxies are put together over time,” Robertson added.

Study co-lead author Sandro Tacchella from the University of Cambridge added, “It is hard to understand galaxies without understanding the initial periods of their development. 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 are thrilled to be able to play a part in revealing this story.

Robertson calculated that the earliest stars would have formed about 225 million years after the Big Bang since star formation in these early galaxies would have started about 100 million years earlier than the age at which they were observed.

Robertson further stated, “We are seeing evidence of star formation about as early as we could expect based on our models of galaxy formation.

Based on photometric analyses of JWST images, other teams have discovered candidate galaxies at even higher redshifts, but these have not yet been verified by spectroscopy. In 2023, JADES will continue with a thorough investigation of a different field, this one centered on the renowned Hubble Deep Field, and then a visit to the Ultra Deep Field for additional deep imaging and spectroscopy.

There are many more candidates in the field that are awaiting spectroscopic investigation, and hundreds more hours have already been approved.

Journal References

Robertson, B. E., et al. (2022) Discovery and properties of the earliest galaxies with confirmed distances. Astrophysics of Galaxies. doi:10.48550/arXiv.2212.04480

Curtis-Lake, E., et al. (2022) Spectroscopy of four metal-poor galaxies beyond redshift ten.

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