The JWST has discovered a plethora of bright galaxy candidates in the early Universe. The observations challenged our basic understanding of the formation of the earliest galaxies.

Spectroscopy is needed to confirm the original nature of these candidates and to understand how the first galaxies form and grow stars. In a new study, astronomers presented deep spectroscopic and continuous ALMA observations of the galaxy GHZ2/GLASS-z12.

Astronomers from the National Astronomical Observatory of Japan and Nagoya University have collaborated on a new study measuring the cosmic age of a distant galaxy: GHZ2/GLASS-z12. Using the ALMA radio telescope array, they discovered a radio signal that travels about 97% of the universe’s lifetime. The discovery of galaxies in the very early universe by the James Webb Space Telescope is now confirmed by this finding.

Because it takes so long for light from distant galaxies to reach us, the expansion of the Universe has caused the color of this light to shift toward the red end of the visible light spectrum, or what’s known as redshift. As a result, GHZ2/GLASS-z12 was one of the most convincing candidates for a distant galaxy that was noticed for its red color.

Two early stage researchers from Nagoya University and the National Astronomical Observatory of Japan used the 40 radio telescopes of the ALMA array in Chile to search for a spectral line shortly after the discovery of these early galaxy candidates to confirm the true age of the galaxies.

To search for an emission line associated with oxygen at the expected frequency of the JWST observations, ALMA pointed to GHZ2/GLASS-z12. Due to the relatively fast time frame for oxygen to form in distant galaxies, the team decided to look for an oxygen emission line to increase the chances of detection.

ALMA was able to find the emission line around the location of the galaxy by integrating the signals from each of its 12 m telescopes. According to the line’s observed redshift, we can see the universe as only 367 million years after the Big Bang.

Lead author Tom Bakx of Nagoya University said: “The first images from the James Webb Space Telescope revealed so many early galaxies that we felt we should test the results using the best observatory on Earth. It was a very exciting time to be an observing astronomer, and we were able to track the status of the observations that will test the JWST results in real time.

“We were initially concerned about the small variation in position between the detected oxygen emission line and the galaxy that Webb sees, but we have performed detailed testing on the observations to confirm that this is a robust detection, which is very difficult to explain by any other interpretation.”

Co-lead author Jorge Zavala of the National Astronomical Observatory of Japan adds: “The bright line emission indicates that this galaxy has rapidly enriched its gas reservoirs with elements heavier than hydrogen and helium. This gives us clues about the formation and evolution of the first generation of stars and their lifespans. The small separation between the oxygen gas and the emission from the stars could also indicate that these early galaxies suffered from explosions that pushed the gas away from the center of the galaxy to the surrounding galaxy and even beyond.”

“These deep ALMA observations provide robust evidence for the existence of galaxies in the first few hundred million years after the Big Bang and confirm the surprising results of the Webb observations. JWST’s work is just beginning, but we are already adapting our models of galaxy formation in the early Universe to these observations. The combined power of Webb and the radio telescope array ALMA gives us the confidence to push our cosmic horizon ever closer to the dawn of the universe.”

Magazine reference:

  1. Tom JLC Bakx, Jorge A Zavala et al. Deep ALMA redshift survey of az∼12 GLASS-JWST candidate galaxy. Monthly communications from the Royal Astronomical Society. DOI: 10.1093/mnras/stac3723