Astronomers report most distant known galaxies, detected and confirmed by JWST
Spectroscopic observations with JWST confirm four early galaxies dating back to less than 400 million years after the Big Bang, three of which are the most distant confirmed to date
Peer-Reviewed PublicationIMAGE: 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 (SHOWN AT LEFT), 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 (SHOWN AT RIGHT). FOUR OF THE GALAXIES STUDIED ARE PARTICULARLY SPECIAL, AS THEY WERE REVEALED TO BE AT AN UNPRECEDENTEDLY EARLY EPOCH. THESE GALAXIES DATE BACK TO LESS THAN 400 MILLION YEARS AFTER THE BIG BANG, WHEN THE UNIVERSE WAS ONLY 2% OF ITS CURRENT AGE. IN THE BACKGROUND IMAGE BLUE REPRESENTS LIGHT AT 1.15 MICRONS (115W), GREEN IS 2.0 MICRONS (200W), AND RED IS 4.44 MICRONS (444W). IN THE CUTOUT IMAGES BLUE IS A COMBINATION OF 0.9 AND 1.15 MICRONS (090W+115W), GREEN IS 1.5 AND 2.0 MICRONS (150W+200W), AND RED IS 2.0, 2.77, AND 4.44 MICRONS (200W+277W+444W). view more
CREDIT: IMAGE: NASA, ESA, CSA, M. ZAMANI (ESA/WEBB), LEAH HUSTAK (STSCI) SCIENCE: BRANT ROBERTSON (UC SANTA CRUZ), S. TACCHELLA (CAMBRIDGE), E. CURTIS-LAKE (UOH), S. CARNIANI (SCUOLA NORMALE SUPERIORE), JADES COLLABORATION
An international team of astronomers has discovered the earliest and most distant galaxies confirmed to date using data from the James Webb Space Telescope (JWST). The telescope captured light emitted by these galaxies more than 13.4 billion years ago, which means the galaxies date back to less than 400 million years after the Big Bang, when the universe was only 2% of its current age.
Initial observations from JWST yielded several candidate galaxies at extreme distances, as had earlier observations with the Hubble Space Telescope. Now, four of these targets have been confirmed by obtaining long spectroscopic observations, which not only provide secure measurements of their distances, but also allow astronomers to characterize the physical properties of the galaxies.
“We’ve discovered galaxies at fantastically early times in the distant universe," said Brant Robertson, professor of astronomy and astrophysics at UC Santa Cruz. “With JWST, for the first time we can now find such distant galaxies 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 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 with redshifts higher 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 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.
“These are well beyond what we could have imagined finding before JWST,” Robertson said. “At redshift 13, the universe is only about 325 million years old.”
Robertson and Emma Curtis-Lake from the University of Hertfordshire (U.K.) will be presenting the new findings on December 12 at a Space Telescope Science Institute (STScI) conference in Baltimore on “First Science Results from JWST.” They are the lead authors of two papers on the results that have not yet been through the peer-review process (see links below).
The observations result from a collaboration of scientists who led the development of two of the instruments onboard Webb, the Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrograph (NIRSpec). The investigation of the faintest and earliest galaxies was the leading motivation in the concepts for these instruments. In 2015, the instrument teams joined together to propose the JWST Advanced Deep Extragalactic Survey (JADES), an ambitious program that has been allocated just over one month of the telescope’s time and is designed to provide a view of the early universe unprecedented in both depth and detail. 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 joined together to execute this observing program,” said Marcia Rieke, NIRCam principal investigator 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 for over 20 years with nearly all large telescopes. The JADES team observed the field in nine different infrared wavelength ranges, capturing exquisite images that reveal 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 the light from 250 faint galaxies. This yielded 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 figure out how many stars they have,” Robertson said. “Now we can start to really pick apart how galaxies are put together over time.”
Coauthor Sandro Tacchella from the University of Cambridge in the United Kingdom 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’re thrilled to be able to play a part in revealing this story.”
According to Robertson, 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.
“We are seeing evidence of star formation about as early as we could expect based on our models of galaxy formation,” he said.
Other teams have identified candidate galaxies at even higher redshifts based on photometric analyses of JWST images, but these have yet to be confirmed by spectroscopy. JADES will continue in 2023 with a detailed study of another field, this one centered on the iconic Hubble Deep Field, and then a return to the Ultra Deep Field for another round of deep imaging and spectroscopy. Many more candidates in the field await spectroscopic investigation, with hundreds of hours of additional time already approved.
The following papers on the new findings have been submitted for publication and are available online:
“Discovery and properties of the earliest galaxies with confirmed distances” (https://arxiv.org/abs/2212.04480)
“Spectroscopy of four metal-poor galaxies beyond redshift ten” (https://t.co/QIy5bDmqwL)
ARTICLE TITLE
Discovery and properties of the earliest galaxies with confirmed distances
Hubble detects ghostly glow surrounding our solar system
IMAGE: THIS ARTIST'S ILLUSTRATION SHOWS THE LOCATION AND SIZE OF A HYPOTHETICAL CLOUD OF DUST SURROUNDING OUR SOLAR SYSTEM. ASTRONOMERS SEARCHED THROUGH 200,000 IMAGES AND MADE TENS OF THOUSANDS OF MEASUREMENTS FROM HUBBLE SPACE TELESCOPE TO DISCOVER A RESIDUAL BACKGROUND GLOW IN THE SKY. BECAUSE THE GLOW IS SO SMOOTHLY DISTRIBUTED, THE LIKELY SOURCE IS INNUMERABLE COMETS – FREE-FLYING DUSTY SNOWBALLS OF ICE. THEY FALL IN TOWARD THE SUN FROM ALL DIFFERENT DIRECTIONS, SPEWING OUT AN EXHAUST OF DUST AS THE ICES SUBLIMATE DUE TO HEAT FROM THE SUN. IF REAL, THIS WOULD BE A NEWLY DISCOVERED ARCHITECTURAL ELEMENT OF THE SOLAR SYSTEM. view more
CREDIT: NASA, ESA, AND ANDI JAMES (STSCI)
Aside from a tapestry of glittering stars, and the glow of the waxing and waning Moon, the nighttime sky looks inky black to the casual observer. But how dark is dark?
To find out, astronomers decided to sort through 200,000 images from NASA's Hubble Space Telescope and made tens of thousands of measurements on these images to look for any residual background glow in the sky, in an ambitious project called SKYSURF. This would be any leftover light after subtracting the glow from planets, stars, galaxies, and from dust in the plane of our solar system (called zodiacal light).
When researchers completed this inventory, they found an exceedingly tiny excess of light, equivalent to the steady glow of 10 fireflies spread across the entire sky. That's like turning out all the lights in a shuttered room and still finding an eerie glow coming from the walls, ceiling, and floor.
The researchers say that one possible explanation for this residual glow is that our inner solar system contains a tenuous sphere of dust from comets that are falling into the solar system from all directions, and that the glow is sunlight reflecting off this dust. If real, this dust shell could be a new addition to the known architecture of the solar system.
This idea is bolstered by the fact that in 2021 another team of astronomers used data from NASA's New Horizons spacecraft to also measure the sky background. New Horizons flew by Pluto in 2015, and a small Kuiper belt object in 2018, and is now heading into interstellar space. The New Horizons measurements were done at a distance of 4 billion to 5 billion miles from the Sun. This is well outside the realm of the planets and asteroids where there is no contamination from interplanetary dust.
New Horizons detected something a bit fainter that is apparently from a more distant source than Hubble detected. The source of the background light seen by New Horizons also remains unexplained. There are numerous theories ranging from the decay of dark matter to a huge unseen population of remote galaxies.
"If our analysis is correct there's another dust component between us and the distance where New Horizons made measurements. That means this is some kind of extra light coming from inside our solar system," said Tim Carleton, of Arizona State University (ASU).
"Because our measurement of residual light is higher than New Horizons we think it is a local phenomenon that is not from far outside the solar system. It may be a new element to the contents of the solar system that has been hypothesized but not quantitatively measured until now," said Carleton.
Hubble veteran astronomer Rogier Windhorst, also of ASU, first got the idea to assemble Hubble data to go looking for any "ghost light." "More than 95% of the photons in the images from Hubble's archive come from distances less than 3 billion miles from Earth. Since Hubble's very early days, most Hubble users have discarded these sky-photons, as they are interested in the faint discrete objects in Hubble's images such as stars and galaxies," said Windhorst. "But these sky-photons contain important information which can be extracted thanks to Hubble's unique ability to measure faint brightness levels to high precision over its three decades of lifetime."
A number of graduate and undergraduate students contributed to project SKYSURF, including Rosalia O'Brien, Delondrae Carter and Darby Kramer at ASU, Scott Tompkins at the University of Western Australia, Sarah Caddy at Macquarie University in Australia, and many others.
The team's research papers are published in The Astronomical Journal and The Astrophysical Journal Letters.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble and Webb science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
JOURNAL
The Astronomical Journal
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-sky Surface-brightness Measurements: II. First Limits on Diffuse Light at 1.25, 1.4, and 1.6 μm
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