Ancient starburst galaxies that formed 2-3 billion years after the Big Bang are unusually hot and contain unexpected elements like nickel, according to a new analysis of CECILIA (Controlled Chemical Evolution Using Ionized Lines in the Interstellar Aurora) data.
This web image shows member galaxies of the galaxy cluster A2744-z7p9OD. Image credit: NASA / ESA / CSA / T. Morishita, IPAC / A. Pagan, STScI.
During the youth of the Universe, many galaxies experienced periods of intense star formation.
Today, some galaxies, like our own Milky Way, are still forming new stars, though not as fast. Other galaxies have stopped forming stars altogether.
This new work will help astronomers understand the reasons behind these different trajectories.
„We’re trying to understand how galaxies have grown and changed over 14 billion years of cosmic history,” said Dr. Alison Strom, an astronomer at Northwestern University.
„Using the NASA/ESA/CSA James Webb Space Telescope, our project targets 'teenage’ galaxies as they go through a chaotic period of growth and change.”
Dr Strom and colleagues analyzed spectra from 33 distant galaxies, breaking their light into its component wavelengths.
„We averaged the spectra from all 33 galaxies to create the deepest spectrum of a distant galaxy ever seen—it would take 600 hours of telescope time to replicate,” said Dr. Gwen Rudy, an astronomer at Carnegie Laboratories.
„This enabled us to create an atlas that will inform future web observations of very distant objects.”
Using the spectra, astronomers were able to identify eight distinct elements: hydrogen, helium, nitrogen, oxygen, silicon, sulfur, argon, and nickel.
„These elements in these galaxies are not surprising, but our ability to measure their light is unprecedented and shows the power of the Web,” Dr Rudy said.
All elements heavier than hydrogen and helium form inside stars.
When stars explode in violent events such as supernovae, they expel these elements into the cosmic atmosphere, where they combine into the next generation of stars.
Therefore, by revealing the presence of certain elements in these early galaxies, astronomers can learn about how star formation changes during their evolution.
The authors were surprised by the presence of nickel, which is difficult to observe.
„I never dreamed we’d see nickel. Even in nearby galaxies, people don’t notice it,” said Dr. Strom.
„A galaxy must have enough of an element and the right conditions to observe it.”
„No one talks about observing nickel. The elements glow in the gas so we can see them.
„Therefore, for us to see nickel, there must be something special about the stars within the galaxies.”
Teenage galaxies were also very hot: the hottest pockets of galaxies could reach 9,700°C, while early galaxies could exceed 13,350°C.
„We expected these early galaxies to have a very different chemistry from our own Milky Way and the galaxies around us today,” Dr Rudy said.
„But we were still surprised by what Webb revealed.”
The invention is described in a Paper In Astrophysical Journal Letters.
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Alison L. Strom and many others. 2023. Cecilia: Faint emission-line spectra of z ∼ 2–3 star-forming galaxies. APJL 958, L11; doi: 10.3847/2041-8213/ad07dc
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