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Age of ancient galaxy discovered by Webb confirmed using ALMA

Since the James Webb Space Telescope launched in December 2021, astronomers and the public have been excited to see how powerful this new tool is, and how it has been able to see some of the most distant galaxies ever observed. However, as cutting-edge science, some of these early results have been contentious as astronomers work to figure out how accurate the data is, due to issues like calibration of the instruments.

Another way to verify results is to look for supporting evidence from other tools, such as recent work using the Atacama Large Millimeter/submillimeter Array or ALMA, a ground-based array of telescopes located in Chile, which has confirmed the age of a very distant galaxy using the detection of oxygen.

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A distant JWST-identified galaxy, GHZ2/GLASS-z12.
The radio telescope array ALMA has pinpointed the exact cosmic age of a distant JWST-identified galaxy, GHZ2/GLASS-z12, at 367 million years after the Big Bang. ALMA’s deep spectroscopic observations revealed a spectral emission line associated with ionized oxygen near the galaxy, which has been shifted in its observed frequency due to the expansion of the Universe since the line was emitted. This observation confirms that the JWST is able to look out to record distances, and heralds a leap in our ability to understand the formation of the earliest galaxies in the Universe. NASA / ESA / CSA / T. Treu, UCLA / NAOJ / T. Bakx, Nagoya U.

A group of researchers from Nagoya University and the National Astronomical Observatory of Japan looked at a galaxy named GHZ2 or GLASS-z12, which was first identified in the James Webb GLASS survey. To see if the galaxy really was as old as it appeared to be, the researchers used ALMA to perform a technique called spectroscopy, in which light coming from the target is broken down into different wavelengths. This shows which wavelengths are missing because they have been absorbed by a particular element — in this case, oxygen.

The research looked at the emission line of oxygen and confirmed its redshift, which refers to the shifting of light from a distant target toward the red end of the spectrum due to the expansion of the universe. This allowed them to confirm that galaxy GLASS-Z12 is extremely old, dating back to 367 million years after the Big Bang.

“The first images of the James Webb Space Telescope revealed so many early galaxies, that we felt we had to test its results using the best observatory on Earth,” said lead author Tom Bakx of Nagoya University in a statement. “It was a very exciting time to be an observational astronomer, and we could track the status of the observations that will test the JWST results in real time.”

The finding supports the fact that the galaxies observed by Webb include some of the oldest galaxies known, demonstrating how powerful our tools now are for looking back to the early stages of the universe.

“These deep ALMA observations provide robust evidence of the existence of galaxies within the first few hundred million years after the Big Bang, and confirms the surprising results from the Webb observations,” said Jorge Zavala of the National Astronomical Observatory of Japan. “The work of JWST has only just begun, but we are already adjusting our models of how galaxies form in the early Universe to match these observations. The combined power of Webb and the radio telescope array ALMA give us the confidence to push our cosmic horizons ever closer to the dawn of the Universe.”

The research is published in the journal Monthly Notices of the Royal Astronomy Society.

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