Very ancient galaxy proto-clusters are merging

The SPT2349-56 proto-cluster (Image ESO/ALMA (ESO/NAOJ/NRAO)/Miller et al.)
The SPT2349-56 proto-cluster (Image ESO/ALMA (ESO/NAOJ/NRAO)/Miller et al.)

Two articles, one published in the journal “Nature” and one in the journal “Astrophysical Journal”, describe the observations of the merger among various starburst galaxies, characterized by a remarkable production of stars. Two teams, led by Tim Miller of Dalhousie University in Canada and Yale University in the USA, and Iván Oteo of the Scottish University of Edinburgh used the ALMA and APEX radio telescopes to study these events which are very ancient as they happened about 1.5 billion years after the Big Bang.

Tim Miller’s team, who published the article on “Nature”, used the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope, inaugurated in March 2013, to observe a proto-cluster called SPT2349-56 consisting of 14 starburst galaxies that now appear in an area with a diameter only four times that of the Milky Way.

The researchers carried out simulations to try to understand how this proto-cluster will evolve and the result is that they will merge into one large galaxy. Given the enormous distance, about 12.4 billion light years, this must have already happened so it’s a great opportunity to see the evolution of that galaxy cluster. A further reason of interest is the remarkable rate of birth of the stars within them, between 50 and 1,000 times higher than that in the Milky Way.

Iván Oteo’s team, who published the article on “Astrophysical Journal”, used the ALMA and APEX (Atacama Pathfinder Experiment) radio telescopes to find a similar situation with at least 10 starburst galaxies nicknamed dusty red core because of its very red color. Finding a group of starburst galaxies together was a surprise because that activity is supposed to last very little in astronomical terms as it causes a considerable consumption of gas to create new stars.

These clusters were discovered thanks to observations made conducted the South Pole Telescope (SPT in the top image) and with ESA’s Herschel Space Observatory. To understand the nature of what were weak spots of light the researchers used the APEX radio telescopes and especially ALMA, which allowed them to identify them as galaxy proto-clusters.

According to current models, proto-clusters of those size were born for the first time about 3 billion years after the Big Bang but the observations indicate that the two identified in these researches are far older. In short, a further surprise arrived thanks to the power and sensitivity of an instrument such as the ALMA radio telescope.

According to ESO astronomer Carlos De Breuck this is just the tip of the iceberg because further observations with the APEX radio telescope show that the actual number of galaxies with star formation is probably even three times. The MUSE instrument installed on the ESO VLT is now also used in follow-up observations to identify more galaxies.

Basically, the researches published are only the beginning because the discoveries of these galaxy proto-clusters raised new questions. New studies are needed to try to understand why those proto-clusters evolved so quickly, again pushing our looks to periods when the universe was still very young.

Artist's concept of the SPT2349-56 proto-cluster (Image ESO/M. Kornmesser)
Artist’s concept of the SPT2349-56 proto-cluster (Image ESO/M. Kornmesser)

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