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Astronomers first saw the glow of the gas shells of ancient galaxies

Deep observations with the MUSE spectrograph on the Very Large Telescope ESO have shown that remote galaxies are surrounded by giant atomic hydrogen tanks
ESA / Hubble & NASA, ESO / Lutz Wisotzki et al.

Galaxies in the young universe were surrounded by giant reservoirs of atomic hydrogen – astronomers for the first time managed to see their weak glow, which in past ages covered almost the whole sky, reports the European Southern Observatory. The results of the work of scientists are given in an article published in the journal Nature .

In 2004, the Hubble Space Telescope observed the area in the constellation Pecs for 270 hours, which later became known as the Hubble Ultra Deep Field (HUDF). With the help of the data obtained by him, the scientists compiled an extremely detailed map of this section of the sky, which showed that an area that looked like other dark telescopes to dark telescopes obscured thousands of distant galaxies. Now the researchers used the MUSE receiver, installed on the VLT telescope, to look even deeper.

A group of scientists led by Lutz Wisotzki of the Potsdam Astrophysical Institute observed the Hubble Ultra Deep Field site in 2014 and 2016 for 58 hours. Unexpectedly for themselves, they found that almost the entire sky area they observe emits on the Lyman-alpha hydrogen line . Such “luminescence” arises as a result of electronic transitions in hydrogen atoms. At the same time, ultraviolet radiation with a wavelength of 122 nanometers is emitted, which is completely absorbed by the earth’s atmosphere. Typically, Lyman-alpha radiation is typical for scattered clouds of neutral hydrogen with temperatures on the order of 10 4 -10 5  kelvins.

The registration of Lyman alpha radiation in the HUDF region means that astronomers have for the first time been able to see the weak emission of the gas shells of the earliest galaxies (redshift z from 3 to 6). In the published composite Lyman-alpha image, the radiation shown in blue is superimposed on the conventional optical field HUDF.

Scientists do not know why hydrogen clouds emit on the Lyman-alpha line. They suggest that this may be due to the influence of ultraviolet background radiation, but in order to accurately answer this question, more research is needed.

“In the future, we plan to perform even more sensitive measurements. We want to determine how these giant space reservoirs of atomic hydrogen are distributed in space, “concludes the head of the group Lutz Visotsky.

In the past, astronomers discovered ancient galaxies that shine brightly only on the Lyman-alpha line. They also could be seen with the help of the MUSE receiver.

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