Astronomers have studied a group of galaxies located more than 12 billion light-years away. The cluster is remarkable because it is at an understudied intermediate stage of formation.
About a large protoscope SPT2349-56 scientists have known for more than a year. It contains one of the most active star-forming zones, but it was not possible to estimate the total stellar mass of the entire system more accurately because the light was too dim. Without these data, it was impossible to tell whether the active star formation was the result of favorable conditions or a direct consequence of the mass of the entire system.
The authors of the new study made observations in the deep optical and infrared ranges, analytically improved the accuracy of the data, identified new galaxies, determined their masses, and used computer simulations to confirm that the superconjunction is at an understudied stage of formation. A scientific paper on the discovery was published in Monthly Notices of the Royal Astronomical Society.
Clusters of galaxies are the nodes of the "cosmic web," the large-scale structure of our Universe. These nodes are "connected" to each other by galactic threads, with relatively empty spaces stretching between them. It is known that these clusters were formed due to small variations in density of primary matter of the Universe, which we see in relict radiation.
Relict radiation is well studied, as are large clusters of galaxies formed over time, because these are the fundamental "building blocks" of the Universe. But scientists still lack the observational data to build accurate computer models of how such massive structures emerged from density fluctuations.
"Modern" clusters of galaxies are clearly visible because their intergalactic gas has been heated during their formation and now glows in the X-ray range. But at distances of ten billion light years or more (at a redshift greater than 2) the radiation becomes almost indistinguishable, so ancient objects are sought through mapping the sky in the infrared and submillimeter ranges.
In recent years, a method that has been developed to study relict radiation has become popular. It involves large-scale scans of the sky in the submillimeter and millimeter range with an accuracy of a few arcminutes. This is how they found many candidates for further study, including SPT2349-56.
Astronomers have learned a lot about this object over the years, but the latest observations with Hubble and the Spitzer telescope's infrared camera have greatly improved the accuracy of the data and identified new galaxies in it.
We now know that SPT2349-56 has more than 30 submillimeter galaxies, that is, galaxies in the process of merging with high rates of star formation. And there are also several dozens of little visible galaxies (LBG- and LAE-galaxies). Analysis of interstellar gas showed that the galaxies are in the last stages of star formation. And the prediction of their further development coincides with the observations of closer to us clusters.
In general, SPT2349-56 is indeed a protoscoping of galaxies at an understudied intermediate stage of the evolution of such objects. Its star formation rate exceeds 10 thousand solar masses per year. We see it as it was when the Universe was only a few billion years old. The galaxies there are younger than our Milky Way.
Although the object was chosen for further study because of its brightness, the galaxies that make it up are themselves ordinary - not too bright and massive. The only exception was C6, which is located in the center of the merger of 20 galaxies and, according to calculations, will be the brightest galaxy of the cluster. More precisely, it has become, but the light of these events will reach us in hundreds of millions of years. The main conclusion of the study is that star formation proceeds there in the same way as in more studied and closer to us clusters.