The structure of the universe is often described as a web of particles and objects, with the largest objects being clusters of galaxies. The structures seen today are believed to have been created by small-amplitude density fluctuations which grew until they collapsed into them. The details of present-day galaxy clusters are well- described, but the intermediate phases of evolution don't have enough observations to constrain the models. It is assumed that the objects have had enough time to equilibrate so that the intergalactic gas has heated up enough to be detected. Astronomers use brightIR or sub millimeter emission to detect the more distant galaxies that are too faint to be seen in the X-ray.
The light from the South Pole Telescope has traveled for over 12 billion years. It is home to over thirty sub millimeter-bright galaxies and dozens of other star forming galaxies. It is one of the most active star forming complexes in the world. The merger of over twenty galaxies seems to be one of its bright sources. It was not possible to know if the huge burst of stars was the result of an efficient system or simply arose because the system was so large.
Matthew Ashby was a member of the team that completed very deep observations at optical and IR wavelength to obtain the stellar mass. They used the Hubble Space Telescope and the IRAC camera to get the data. To model the SEDs, a lot of point sources need to be matched. This is a complex undertaking, and the scientists describe the processes for doing so, as well as addressing the serious blend that can occur due to inadequate spatial resolution.
According to their results published in Monthly Notices of the Royal Astronomical Society, the stellar mass in this primordial cluster as compared with its star formation rate is close to the value measured in nearby "normal" galaxies. The activity is nearing the end of this tumultuous phase as the gaseous raw material for stars is being dissipated.
More information: Ryley Hill et al, Rapid build-up of the stellar content in the protocluster core SPT2349−56 at z = 4.3, Monthly Notices of the Royal Astronomical Society (2021). DOI: 10.1093/mnras/stab3539 Journal information: Monthly Notices of the Royal Astronomical Society
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