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Alma observes the oldest galaxy fusion known to date

By teaming up with Hubble, Alma has identified the most distant and oldest galaxy fusion known to date. Named B14-65666, it was 13 billion years old in the constellation Sextant.

The most distant galaxy and therefore the oldest known to date of humanity is called GN-z11. It was the Hubble telescope that found it a few years ago in the constellation Ursa Major. We observe it as it was about 13.4 billion years ago. The images provided by galaxies more than 13 billion years old still have a low resolution in the instruments that observe them while trying to unravel the secrets of the birth and evolution of the first galaxies. Significant progress in this regard should be made when the JWST, the James-Webb Space Telescope, will see its first light by 2021.

The article published today in Publications of the Astronomical Society of Japan by a team of mostly Japanese researchers – which is available on arXiv – does not beat the distance record for a galaxy. But the team of astronomers led by Takuya Hashimoto of Waseda University in Japan still beats a record thanks to the Atacama Large Millimeter / submillimeter Array (Alma).

UV emissions 100 times more intense than for the Milky Way

The radio telescope has indeed established that the object called B14-65666 was the most distant collision of galaxies discovered so far because it occurred 13 billion years ago as we observe today. Although the image obtained in the millimetric domain is still very vague, it benefits from Alma’s resolution power, which is 10 times greater than that of Hubble. The space telescope had already allowed him to observe B14-65666 in the field of ultraviolet (UV). The images showed two brighter regions, but they were still difficult to interpret.

By combining observations of Alma and Hubble, astrophysicists have identified the emissions produced by atoms of oxygen to carbon, dust and stars. Above all, the two regions highlighted by Hubble move at different speeds, which in the end makes it possible to seriously advance the hypothesis that we are in the presence of an ongoing fusion of two galaxies with a total mass only 10% of that of the Milky Way. However, UV emissions are 100 times higher than in our galaxy, which implies a surge of formation of new stars, a phenomenon typical of more recent galaxy fusions.

These observations are well in line with the standard cosmological model which predicts that the oldest colliding galaxies are small and will later give rise to larger galaxies, which will also collide with each other and the dwarf galaxies still present.

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