Ancient galactic clusters

A survey conducted by the Subaru telescope reveals an unexpected level of abundance of chemical elements heavier than hydrogen and helium in the gas that consists of two galaxies in the universe remote clusters.
Two clusters of primordial galaxies, at about eleven billion light years from us, have been studied by a team of researchers led by Rhythm Shimakawa National Astronomical Observatory of Japan to investigate the processes of star formation and evolution of galaxies in early universe.
The researchers used the instrument MOIRCS, near-infrared spectrograph installed at the Subaru telescope located in the archipelago of Hawaii. Starting point of the investigation, the collection of data from observations conducted on protoammassi, which are located in the regions corresponding to the radio galaxies PKS 1138-262 and 1588-033 USS, in the direction of the constellation Serpens.


Credit: NAOJ/HST

Thanks to the information gathered, the team was able to estimate the total mass of the two structures, which is both equal to approximately one hundred thousand billion times that of our Sun, or about 100 times that of our own galaxy, the Milky Way. Values that the researchers are in line with the evolutionary history of galaxy clusters and that make these celestial objects laboratories for exploring the early stages of galaxy formation in a so dense matter. The investigation was focused on the abundances of elements heavier than hydrogen and helium (what astronomers call generically ‘metals’) in the gas of the galaxies, showing higher values than the average values observed in other galaxies at distances similar.
To explain this excess of metallicity, the researchers place their own focus on the environmental effects of growth and leakage of gas durations processes of galaxy formation, that is related to cumulative phenomena due to the large presence of galaxies in these clusters. Recent studies indicate that in fact, as these effects have been felt to a greater extent in the evolution of galaxies precisely around 11 billion years ago, when they were 100 times more intense than today. Galactic clusters are structures in which galaxies and the ionized gas are held together by the presence of large concentrations of dark matter. The galaxies that compose them can reach speeds of more than 3 million kilometers per hour. Just like when we move, with a good rhythm, bicycle or motorbike, we perceive the strength of the wind, so even those galaxies in their motion are subject to considerable pressure due to the gas present in the cluster. According Shimakawa and his colleagues, this friction could rip off the gas to the galaxies themselves of their outermost regions and metal-poor, while maintaining the more enriched, located in the central regions, intact. A second hypothesis suggests that the pressure produced by the intergalactic medium prevents the galaxies on their gas rich in heavy elements to escape, thus helping to raise the value of the levels observed abundances.
“Both solutions are plausible,” says Gabriella De Lucia, researcher INAF Astronomical Observatory of Trieste. “There are others that the authors believe less likely, for example, that the different metallicity is due simply to a more rapid development of the regions which are intended to form a cluster. It ‘something that you would expect, at least to some extent, in the cosmological scenario that we consider valid. There are many uncertainties to be taken into account, both on the observational estimates that on theoretical arguments used, and certainly would be interesting to see whether this is a result of generic, that is, for each region of proto-cluster. To support the interpretation of the data would be useful against more detailed with what are the expectations using theoretical models of galaxy formation, such as those developed by our team here at the Astronomical Observatory of Trieste.

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