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ALMA Confirms Discovery of Oxygen-Rich Galaxy in Very Early Universe

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GHZ2/GLASS-z12, initially identified in the JWST GLASS survey, existed when the Universe was only 367 million years old (redshift z=12.117).

This image shows the distant galaxy GHZ2/GLASS-z12. Image credit: NASA / ESA / CSA / T. Treu, UCLA / NAOJ / T. Bakx, Nagoya University.

GHZ2/GLASS-z12 was identified in the JWST GLASS survey, a survey that observes the distant Universe and behind massive clusters of galaxies.

These observations consist of several images using different broad-band color filters, similar to the separate RGB colors in a camera.

For distant galaxies, the light takes such a long time to reach us that the expansion of the Universe has shifted the color of this light towards the red end of the visible light spectrum in the so-called redshift.

The red color of GHZ2/GLASS-z12 consequently helped astronomers identify it as one of the most convincing candidates for a distant galaxy they observed.

So many bright distant galaxies were identified in the first few weeks of Webb observations that it challenged our basic understanding of the formation of the earliest galaxies.

However, these red colors are only indicative of a distant galaxy, and could instead be a very dust-rich galaxy masquerading as a more distant object.

Only direct observations of spectral lines — lines present in a galaxy’s light spectrum used to identify the elements present — can robustly confirm the true distances of these galaxies.

Immediately after the discovery of these early galaxy candidates, Dr. Tom Bakx from Nagoya University and the National Astronomical Observatory of Japan and colleagues used the Atacama Large Millimeter/submillimeter Array (ALMA) to hunt for a spectral line to confirm the true ages of the galaxies.

ALMA pointed at GHZ2/GLASS-z12 to hunt for an emission line associated with oxygen at the expected frequency suggested by the Webb observations.

Oxygen is a typically abundant element in distant galaxies due to its relatively short formation timescale, therefore the authors chose to search for an oxygen emission line to increase chances of detection.

ALMA was able to detect the emission line close to the position of the galaxy.

The observed redshift of the line (z=12.117) indicates we see the galaxy as it was just 367 million years after the Big Bang.

“The first images from Webb revealed so many early galaxies, that we felt we had to test its results using the best observatory on Earth,” Dr. Bakx said.

“It was a very exciting time to be an observational astronomer, and we could track the status of the observations that will test the Webb results in real time.”

“We were initially concerned about the slight variation in position between the detected oxygen emission line and the galaxy seen by Webb, but we performed detailed tests on the observations to confirm that this really is a robust detection, and it is very difficult to explain through any other interpretation.”

“The bright line emission indicates that this galaxy has quickly enriched its gas reservoirs with elements heavier than hydrogen and helium,” said Dr. Jorge Zavala, an astronomer at the National Astronomical Observatory of Japan.

“This gives us some clues about the formation and evolution of the first generation of stars and their lifetime.”

“The small separation we see between the oxygen gas and the stars’ emission might also suggest that these early galaxies suffered from violent explosions that blew the gas away from the galaxy centre into the region surrounding the galaxy and even beyond.”

“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.”

“The work of Webb 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 findings were published in the Monthly Notices of the Royal Astronomical Society.

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Tom J.L.C. Bakx et al. Deep ALMA redshift search of a z ~ 12 GLASS-JWST galaxy candidate. MNRAS, published online December 23, 2022; doi: 10.1093/mnras/stac3723

Source : Breaking Science News

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