A massive supercluster of galaxies in the early universe

A false-color image of the far-infrared emission from a massive protocluster of galaxies (in the circle) dating to the time around 1.4 billion years after the big bang. The astronomers made deep optical and infrared observations of the complex and concluded that the star-forming processes at work, while unusually active, appear to generally follow the same processes seen in our galaxy. Credit: NASA/ESA/Herschel; Miller et al.

The structure of the universe is often described as a cosmic web of filaments, nodes and voids, the nodes being clusters of galaxies, the largest gravitationally bound objects known. These nodes are thought to have been seeded by low amplitude density fluctuations like those seen in the cosmic microwave background (CMB) that grew until they collapsed into the structures seen today. today. Although the CMB is well understood and the details of current galaxy clusters are well described, the intermediate phases of evolution lack sufficient observations to constrain the models. Traditional searches for galaxy clusters assume that these objects have had enough time to equilibrate so that the intergalactic gas has warmed up enough to be detected in the X-ray emission. distant ones that are too faint to be detected in X-rays, astronomers use their bright infrared or sub-millimeter emission instead.

The SPT2349−56 supercluster, discovered in the submillimeter band by the South Pole Telescope, is so distant that its light has been traveling for more than twelve billion years. It is home to more than thirty submillimeter luminous galaxies and dozens of other luminous and/or star-forming galaxies confirmed by spectroscopy. It is one of the most active star-forming complexes known, producing over ten thousand stars a year. One of its light sources appears to be the merger of more than twenty galaxies. The stellar mass of the system, however, was not known, making it impossible, for example, to know whether the huge starburst was the result of extraordinary efficiency or simply occurred because the system was extremely large.

CfA astronomer Matthew Ashby was part of a team that has now performed very deep observations at optical and infrared wavelengths to obtain stellar masses through spectral energy distribution (SED) analyses. They used the Gemini and Hubble space telescopes to obtain optical/near-infrared flux measurements and Spitzer’s IRAC camera for infrared flux. In order to model SEDs, the many detected point sources must be matched to each other at all wavelengths. This is a complex undertaking, and the scientists describe the processes for achieving it while addressing the serious mixing that can occur due to inadequate spatial resolution in the infrared.

According to their results published in Royal Astronomical Society Monthly Notices, astronomers find that the stellar mass of this primordial cluster relative to its rate of star formation is close to the value measured in nearby (“normal”) galaxies, a finding which suggests that star formation processes at work are similar to those of the local universe. The cluster does, however, show a molecular gas deficit, suggesting that activity is nearing the end of this tumultuous phase as the star’s gaseous raw material dissipates.


A massive protocluster of merging galaxies in the early universe


More information:
Ryley Hill et al, Rapid accumulation of stellar content in the core of protocluster SPT2349−56 at z=4.3, Royal Astronomical Society Monthly Notices (2021). DOI: 10.1093/mnras/stab3539

Provided by Harvard-Smithsonian Center for Astrophysics

Quote: A massive galaxy supercluster in the early universe (June 20, 2022) Retrieved June 21, 2022 from https://phys.org/news/2022-06-massive-galaxy-supercluster-early-universe.html

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