Webb completes his first “deep field” with nine days of observation. What did he find?
About 13 billion years ago, stars in the universe’s oldest galaxies sent photons into space. Some of those photons finished their epic journey on the gold-coated beryllium mirrors of the James Webb Space Telescope in the past few months. JWST collected these primordial photons over several days to create its first “Deep Field” image.
One of the primary goals of JWST is to study the first galaxies in the universe. The results will help astrophysicists piece together the history of the universe and how galaxies evolved. These early galaxies are very faint, but the JWST is built to find them.
Many things in nature masquerade as something else. We don’t get close to the truth until scientists apply their skills. Early thinkers believed that everything in the universe revolved around the Earth, placing humanity at the center of everything, a baffling misunderstanding that still baffles humanity to this day. In the end, we figured it out, thanks to Copernicus and those who followed him. The natural features on Mars looked like channels built by a Martian civilization, which made everyone excited and even fooled some scientists. In the end, better telescopes revealed the truth. There are countless examples of this.
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Younger galaxies can disguise themselves as older galaxies, a problem that has plagued our attempts to understand galactic evolution. The early universe was made almost entirely of two lighter and simpler elements, hydrogen and helium. As a result, the stars that make up the oldest galaxies are composed almost entirely of hydrogen and helium. They have a “low metallic” in astrological terms.
Confusingly, some of the younger galaxies also have a low metallicity. It must contain much more than just hydrogen and helium because many stars lived and died before these galaxies formed. And stars are what make up the heavier elements, sending them into space when they die for the next generation of stars to pick up.
But JWST is not easy to fool.
JWST can dissect the light from these galaxies more accurately than any of its predecessors. You have to stay very cold to observe infrared light in such detail, which is why you sit so far out in space, protected by a huge sun shield. The JWST Near Infrared Camera (NIRCam) and Near Infrared Spectrometer (NIRSpec) were used to influence recent monitoring efforts, and the teams operating each instrument collaborated closely to achieve these results.
“It was necessary to prove that these galaxies did indeed inhabit the early universe. It is very possible that the closest galaxies disguised themselves as very distant galaxies,” said astronomer Emma Curtis Lake of the University of Hertfordshire in the UK. “Seeing the spectrum unfolded as we had hoped, confirming that these galaxies are at the true edge of our view, and some are farther away than Hubble can see! It is a very exciting feat of the mission.”
Two upcoming papers will present the new findings from JWST’s deep field observations. The first is “Spectral analysis of four metal-poor galaxies exceeding ten redshifts,” by Curtis Lake et al. 2022. The other is “Discovery and Characteristics of the Earliest Galaxies with Confirmed Distances,” by Robertson et al. 2022. Neither has been peer-reviewed yet.
The Hubble Space Telescope has provided us with deep field observations. When astronomers pointed to a patch of seemingly empty sky and left it collecting photons for more than 11 days in 2003 and 2004, it revealed something unusual. What was masquerading as empty space was filled with galaxies. Its Ultra Deep Field image found nearly 10,000 galaxies in a small patch of dark sky, and astronomers believe that about 800 of the faintest and reddest are some of the primordial galaxies in the universe.
But we needed a more powerful telescope with better instruments to study them.
NIRCam and NIRSpec were built to find these early galaxies, and they succeeded. The team behind both instruments got together before the telescope was completed and launched to develop JADES, the Advanced Deep Extragalactic Survey JWST. JADES will give astronomers an unprecedented, deep and detailed look at the universe’s oldest galaxies. “These results are the culmination of why the NIRCam and NIRSpec teams joined together to implement this monitoring program,” The article was co-authored by Marcia Rieke, a NIRCam principal investigator from the University of Arizona in Tucson.
The JWST’s ability to discern ancient galaxies is based on Lyman’s fracture. The Lyman fracture is related to how light is absorbed by neutral gas in the star-forming regions of distant galaxies. The more distant a galaxy is, the more red its light will turn. This slight expansion puts the Lyman interval in a different position in the spectroscopic observations. The JWST can detect Lyman fractures with its intense infrared capabilities.
The JWST captured its deep field in the same region of the sky as Hubble’s Ultra Deep Field. Telescopes have been studying this region for about 20 years, creating a complete data set across the electromagnetic spectrum. Webb’s notes build on this archive, adding the deepest and most light-sensitive observations to date.
The JWST field is 15 times larger than the Hubble field and is deeper and sharper. The NIRCam image is only about the size of a human when viewed from a mile away, but it contains more than 100,000 galaxies. Because of the power of the JWST, astronomers can be certain that some of them are the oldest galaxies that formed in the universe.
“For the first time, we discovered galaxies only 350 million years after the Big Bang, and we can be absolutely confident of their fantastic distances,” Co-authored by Brant Robertson of the University of California Santa Cruz, a member of the NIRCam science team. “Finding these early galaxies in such stunningly beautiful images is a special experience.”
The team used the telescope’s NIRSpec instrument to examine the light from 250 of the faintest galaxies in the image over a 28-hour period. The spectra provided precise measurements of each of the galaxies’ redshifts, revealing the properties of the stars and gas in each one.
“These are by far the weakest infrared spectra ever captured,” said astronomer and co-author Stefano Cargnani of the Scuola Normale Superiore in Italy. “It reveals what we hoped to see: an accurate measurement of the wavelength of light due to intergalactic hydrogen scattering.”
Of the more than 100,000 galaxies in the JWST Deep Field, the researchers have focused on four of them. All four have a redshift greater than 10, with a redshift of two. They have been traveling for 13.184 billion years. Light from redshift 13 galaxies was among the first light sent into the universe after the Big Bang.
Those are the galaxies astronomers were hoping to spot with JWST, and that’s what the telescope does. These galaxies lit up the cosmic dawn and are essential to understanding how galaxies form and evolve. “Galaxies forming at these times may be the seeds of more massive, mature galaxies in the local universe,” Curtis Lake and co-authors explain in their paper.
The cosmic dawn represents a gap in our understanding of the universe, and attempts to fill that gap rely on a number of assumptions about gas temperature and other factors. But with its precise instruments, astronomers hope the Japanese planet Earth can bridge the data gap.
“It is difficult to understand galaxies without understanding the initial periods of their evolution. As with humans, much of what happens later depends on the influence of these early generations of stars,” said astronomer and co-author Sandro Takela of the University of Cambridge in the United Kingdom. “So many intergalactic questions have been waiting for Webb’s transformative opportunity, and we’re thrilled to be able to play a part in uncovering this story.“
In their paper, Curtis-Lake and her co-authors acknowledge this milestone in cosmology. “We conclude by asserting that this is a distinctly outstanding result of the JWST mission, pushing the boundaries of spectroscopy to a significantly earlier era of galaxy formation,” they wrote.
JWST is only at the beginning of its mission, and finding leaky Lyman points in ancient galaxies is a critical step. “In addition to providing clear detections of Lyman discontinuities up to z = 13.2, the JADES observations also demonstrate the power of spectroscopy for probing the physics of these galaxies and the IGM,” write Curtis Lake and co-authors.
“Really, this is just a starting point for the mission.”
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