This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Astronomers using the James Webb Space Telescope (JWST) have found evidence that a distant, exceptionally blue galaxy may allow most of its ionizing radiation to escape into space. Known as EBG-1, the gravitationally lensed galaxy is seen at a redshift of 9.244, about 530 million years after the Big Bang.
The paper was posted to the arXiv preprint server on Oct. 16. Scientists estimate that cosmic reionization happened roughly between 600 million and a billion years (around redshifts 6 to 8) after the Big Bang and was complete by redshift 5.5. During this epoch, ionizing ultraviolet radiation from early stars and galaxies converted the universe's neutral hydrogen gas into the ionized state we see today.
The ultraviolet radiation driving this transition is mainly made up of Lyman continuum (LyC) photons with wavelengths less than 912 Å. Much of this light is absorbed by gas and dust inside a galaxy, so the fraction that escapes into intergalactic space, called the escape fraction, is key to estimating how much a galaxy contributed. "Which galaxies supplied most of the ionizing photons remains debated," the researchers write in their paper.
Some models suggest that dwarf galaxies are the main drivers, while others point to more massive galaxies with efficient star formation rates. As a result, studying quasars and galaxies from this period and beyond can not only constrain the redshift at which reionization occurred but also provide clues about the main drivers. In this work, astronomers led by Yunjing Wu of the University of Tokyo have presented the spectroscopic analysis of one of the bluest galaxies observed when the universe was only 530 million years old.
At a redshift of 9.244, Extreme Blue Galaxy 1 (EBG-1) is lensed by a foreground galaxy cluster called MACS0647. This means the galaxy cluster's gravity bends and magnifies EBG-1's light, allowing astronomers to see it in detail. The extreme blueness refers to the ultraviolet (UV) light emission of the galaxy.
"[The galaxy] stands out for having one of the bluest UV slopes yet measured at this redshift," researchers say. The UV slope describes how steeply the galaxy's brightness changes with wavelength in the ultraviolet. A very blue slope suggests very little dust, very young stars and a metal-poor composition.
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