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Astronomers Measure Amount of Carbon around Galaxies in Early Universe

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New research led by the Swinburne University of Technology shows that the amount of warm carbon suddenly increased by a factor of five over a period of only 300 million years.

Davies et al. shed new light on the state of the Universe 13 billion years ago by measuring the density of carbon in the gases surrounding ancient galaxies. Image credit: Swinburne University of Technology.

The formation of the first galaxies marked an important turning point in cosmic history.

Massive stars released high energy photons which commenced the reionization of the Universe, and stellar nucleosynthesis led to the production of the first heavy elements, which were then released into the surrounding gas via supernova explosions.

However, relatively little is known about the timing of the formation of the first galaxies and how they shaped the properties of their surrounding environments.

“We found that the fraction of carbon in warm gas increased rapidly about 13 billion years ago, which may be linked to large-scale heating of gas associated with the phenomenon known as the Epoch of Reionization,” said lead author Dr. Rebecca Davies, an astronomer at the Swinburne University of Technology and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions.

While previous studies have suggested a rise in warm carbon, much larger samples were needed to provide statistics to accurately measure the rate of this growth.

“That’s what we’ve done here. And so, we present two potential interpretations of this rapid evolution,” Dr. Davies said.

“The first is that there is an initial increase in carbon around galaxies simply because there is more carbon in the Universe.”

“During the period when the first stars and galaxies are forming, a lot of heavy elements are forming because we never had carbon before we had stars.”

“And so, one possible reason for this rapid rise is just that we’re seeing the products of the first generations of stars.”

“However, we also found evidence that the amount of cool carbon decreased over the same period.”

“This suggests that there might be two different phases in the evolution of carbon — a rapid rise while reionization occurs, followed by a flattening out.”

“The research was built on an exceptional sample of data obtained during 250 hours of observations on ESO’s Very Large Telescope (VLT),” said Dr. Valentina D’Odorico, an astronomer at the Italian Institute for Astrophysics.

“This is the largest amount of observing time assigned to a single project carried out with the X-SHOOTER spectrograph.”

“Thanks to the 8-m VLT we could observe some of the most distant quasars, which act as flashlights, illuminating galaxies along the path from the early Universe to the Earth.”

As the quasar light passes through galaxies in its 13-billion-year journey across the Universe some photons are absorbed, creating distinctive barcode-like patterns in the light, which can be analyzed to determine the chemical composition and temperature of gas in the galaxies.

This gives an historical picture of the development of the Universe.

“These ‘barcodes’ are captured by detectors at VLT’s X-SHOOTER spectrograph,” Dr. Davies said.

“This instrument splits the galaxy light into different wavelengths, like putting light through a prism, allowing us to read the barcodes and measure the properties of each galaxy.”

“Our results are consistent with recent studies showing that the amount of neutral hydrogen in intergalactic space decreases rapidly around the same time.”

“This research also paves the way for future investigations with the Square Kilometre Array which aims to directly detect emission from neutral hydrogen during this key phase of the Universe’s history.”

The findings appear in the Monthly Notices of the Royal Astronomical Society.


Rebecca L. Davies et al. Examining the decline in the Civ content of the Universe over 4.3 ≲ z  ≲ 6.3 using the E-XQR-30 sample. MNRAS 521 (1): 314-331; doi: 10.1093/mnras/stad294

Source : Breaking Science News

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