Astronomers have seen the most distant and dim galaxies in history

Hydrogen halos around ancient galaxies, registered by MUSE ESO / MUSE HUDF team
Hydrogen halos around ancient galaxies, registered by MUSE

Astronomers working with the MUSE receiver on the VLT telescope have completed the deepest spectroscopic review in history. They were  able to measure the physical properties of galaxies that appeared less than a billion years after the Big Bang, and to determine the distance to them. In addition, scientists found 72 candidates in the galaxy, brightly emitting only in the hydrogen line Lyman-alpha, which further indicates their antiquity. The results of the work are described in a press release  on the ESO website, as well as in a special issue  the journal Astronomy & Astrophysics .

A group of researchers led by Roland Bacon from the University of Lyon observed a section of the southern sky in the constellation of the Ovens region, known as the Hubble Ultra Deep Field (HUDF). It was first investigated by the Hubble in 2004 – hence the name. The space telescope was able to “look” very far – in an era when less than a billion years had passed since the Big Bang – and see a lot of different galaxies. Later, the HUDF region was observed many more times by both Hubble and other telescopes, which resulted in one of the  most profound surveys of the universe for today .
Now the Muse receiver connected to the telescope complex was connected to the study Very Large Telescope. With its help astronomers conducted the deepest in the history of astronomy spectroscopic observations. Scientists accurately measured the parameters of 1600 galaxies – over the past decade, using ground-based telescopes in this sector, it was possible to thoroughly investigate about 10 times less objects. The MUSE data allows us to explore very weak and distant galaxies that appeared about 13 billion years ago, when the Universe was still very young. The galaxies that the receiver registers are 100 times fainter than those recorded in previous surveys.

The survey also found 72 candidates in the galaxy, which emit only on the hydrogen line Lyman-alpha . Such radiation is characteristic of very ancient stars. Nevertheless, modern models of star formation can not fully explain why these galaxies are intensively glowing in a single line.

They were able to see these objects thanks to the features of the MUSE spectrograph – it provides a spectrum in each pixel of the frame. MUSE splits the field of view into 24 separate segments, each of which is divided into 48 fragments, which gives a total of 1152 fragments. The spectrograph processes each of the fragments, splitting the light at each point into its constituent colors, forming a spectrum. This allows you to measure the distance, color characteristics and other properties of the observed galaxies – including those that can not be seen with the Hubble telescope.

“What we know about these galaxies – for example, their chemical composition – can only be provided by spectroscopy. And while we do not go through one galaxy behind the galaxy, but we learn everything at once for all galaxies! “, Explains Jarle Brinchmann, the first author of one of the survey results, an associate of the Leiden University in the Netherlands and the Institute of Astrophysics and Space Research (CAUP) in Porto (Portugal).

Another important finding was the systematic recording of bright hydrogen halos around the galaxies of the early Universe. This will allow astronomers to study how matter flows into and out of early galaxies. The published series of articles also says that the data obtained can be used to study the role of weak galaxies in the era of  cosmic reionization  (which began just 500 million years after the Big Bang), the frequency of confluence of galaxies in the young universe, galactic winds, star formation , and the mapping of star motions in the early Universe.

Last year, astronomers published the deepest images of the sky, four times the size of the full moon. They were obtained as part of the Ultra-Deep Survey (UDS) review . The researchers managed to find out more than 250 thousand galaxies, several hundred of which appeared during the first billion years after the Big Bang.

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