MSGID: 1:317/3 642661f7   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Astronomers witness the birth of a very distant cluster of galaxies from   
   the early Universe    
      
     Date:   
         March 30, 2023   
     Source:   
         ESO   
     Summary:   
         Astronomers have discovered a large reservoir of hot gas in the   
         still- forming galaxy cluster around the Spiderweb galaxy -- the   
         most distant detection of such hot gas yet. Galaxy clusters are   
         some of the largest objects known in the Universe and this result   
         further reveals just how early these structures begin to form.   
      
      
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   FULL STORY   
   ==========================================================================   
   Using the Atacama Large Millimeter/submillimeter Array (ALMA), of which   
   ESO is a partner, astronomers have discovered a large reservoir of hot   
   gas in the still-forming galaxy cluster around the Spiderweb galaxy --   
   the most distant detection of such hot gas yet. Galaxy clusters are some   
   of the largest objects known in the Universe and this result, published   
   today in Nature, further reveals just how early these structures begin   
   to form.   
      
      
   ==========================================================================   
   Galaxy clusters, as the name suggests, host a large number of galaxies   
   - - sometimes even thousands. They also contain a vast "intracluster   
   medium" (ICM) of gas that permeates the space between the galaxies   
   in the cluster. This gas in fact considerably outweighs the galaxies   
   themselves. Much of the physics of galaxy clusters is well understood;   
   however, observations of the earliest phases of formation of the ICM   
   remain scarce.   
      
   Previously, the ICM had only been studied in fully-formed nearby   
   galaxy clusters. Detecting the ICM in distant protoclusters -- that is,   
   still-forming galaxy clusters -- would allow astronomers to catch these   
   clusters in the early stages of formation. A team led by Luca Di Mascolo,   
   first author of the study and researcher at the University of Trieste,   
   Italy, were keen to detect the ICM in a protocluster from the early   
   stages of the Universe.   
      
   Galaxy clusters are so massive that they can bring together gas that   
   heats up as it falls towards the cluster. "Cosmological simulations have   
   predicted the presence of hot gas in protoclusters for over a decade,   
   but observational confirmations has been missing," explains Elena   
   Rasia, researcher at the Italian National Institute for Astrophysics   
   (INAF) in Trieste, Italy, and co- author of the study. "Pursuing   
   such key observational confirmation led us to carefully select one of   
   the most promising candidate protoclusters." That was the Spiderweb   
   protocluster, located at an epoch when the Universe was only 3 billion   
   years old. Despite being the most intensively studied protocluster,   
   the presence of the ICM has remained elusive. Finding a large reservoir   
   of hot gas in the Spiderweb protocluster would indicate that the system   
   is on its way to becoming a proper, long-lasting galaxy cluster rather   
   than dispersing.   
      
   Di Mascolo's team detected the ICM of the Spiderweb protocluster through   
   what's known as the thermal Sunyaev-Zeldovich (SZ) effect. This effect   
   happens when light from the cosmic microwave background -- the relic   
   radiation from the Big Bang -- passes through the ICM. When this light   
   interacts with the fast-moving electrons in the hot gas it gains a bit   
   of energy and its colour, or wavelength, changes slightly. "At the right   
   wavelengths, the SZ effect thus appears as a shadowing effect of a galaxy   
   cluster on the cosmic microwave background," explains Di Mascolo.   
      
   By measuring these shadows on the cosmic microwave background,   
   astronomers can therefore infer the existence of the hot gas, estimate   
   its mass and map its shape. "Thanks to its unparalleled resolution and   
   sensitivity, ALMA is the only facility currently capable of performing   
   such a measurement for the distant progenitors of massive clusters,"   
   says Di Mascolo.   
      
   They determined that the Spiderweb protocluster contains a vast reservoir   
   of hot gas at a temperature of a few tens of millions of degrees Celsius.   
      
   Previously, cold gas had been detected in this protocluster, but the   
   mass of the hot gas found in this new study outweighs it by thousands   
   of times. This finding shows that the Spiderweb protocluster is indeed   
   expected to turn into a massive galaxy cluster in around 10 billion years,   
   growing its mass by at least a factor of ten.   
      
   Tony Mroczkowski, co-author of the paper and researcher at ESO, explains   
   that "this system exhibits huge contrasts. The hot thermal component   
   will destroy much of the cold component as the system evolves, and we   
   are witnessing a delicate transition." He concludes that "it provides   
   observational confirmation of long-standing theoretical predictions   
   about the formation of the largest gravitationally bound objects in   
   the Universe."  These results help to set the groundwork for synergies   
   between ALMA and ESO's upcoming Extremely Large Telescope (ELT ), which   
   "will revolutionise the study of structures like the Spiderweb," says   
   Mario Nonino, a co-author of the study and researcher at the Astronomical   
   Observatory of Trieste. The ELT and its state-of-the-art instruments,   
   such as HARMONI and MICADO, will be able to peer into protoclusters and   
   tell us about the galaxies in them in great detail.   
      
   Together with ALMA's capabilities to trace the forming ICM, this will   
   provide a crucial glimpse into the assembly of some of the largest   
   structures in the early Universe.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Galaxies # Stars # Cosmology # Astrophysics # Astronomy   
                   # Big_Bang # Space_Telescopes # Space_Exploration   
       * RELATED_TERMS   
             o Globular_cluster o Spitzer_space_telescope o Dark_matter o   
             Galaxy o Barred_spiral_galaxy o Galaxy_formation_and_evolution   
             o Interstellar_medium o Andromeda_Galaxy   
      
   ==========================================================================   
   Story Source: Materials provided by ESO. Note: Content may be edited   
   for style and length.   
      
      
   ==========================================================================   
   Related Multimedia:   
       * The_Sunyaev-Zeldovich_effect_in_the_Spiderweb_protocluster   
   ==========================================================================   
   Journal Reference:   
      1. Luca Di Mascolo, Alexandro Saro, Tony Mroczkowski, Stefano Borgani,   
         Eugene Churazov, Elena Rasia, Paolo Tozzi, Helmut Dannerbauer,   
         Kaustuv Basu, Christopher L. Carilli, Michele Ginolfi, George Miley,   
         Mario Nonino, Maurilio Pannella, Laura Pentericci, Francesca   
         Rizzo. Forming intracluster gas in a galaxy protocluster   
         at a redshift of 2.16. Nature, 2023; 615 (7954): 809 DOI:   
         10.1038/s41586-023-05761-x   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230330102341.htm   
      
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