An international team of astronomers using data from two ESA’s space telescopes, Planck and Herschel, has identified more than 200 proto-clusters of galaxies in the distant Universe, many of which were magnified by other galaxies lying in front of them via gravitational lensing.
The Planck all-sky map at submillimeter wavelengths; the band running through the middle corresponds to dust in the Milky Way Galaxy; the black dots indicate the location of the proto-cluster candidates identified by Planck and subsequently observed by Herschel. The inset images showcase some of the observations made by Herschel’s SPIRE instrument; the contours represent the density of galaxies. Image credit: ESA / Planck Collaboration / H. Dole / D. Guéry / G. Hurier / IAS / University Paris-Sud / CNRS / CNES.
Galaxies like our own are usually not found in isolation. In the Universe today, 13.8 billion years after the Big Bang, many are in dense clusters of tens, hundreds or even thousands of galaxies. Pinpointing when and how these clusters formed should provide insight into the process of galaxy cluster evolution, including the role played by dark matter in shaping these cosmic ‘metropolises.’
Now, the team led by Dr Hervé Dole of the Institut d’Astrophysique Spatiale in Orsay and the Institut Universitaire de France in Paris has found 228 objects in the distant Universe, seen at a time when it was only 3 billion years old, which could be precursors of the clusters seen around us today.
To find these galactic gems, the scientists first mined the Planck all-sky maps, looking for the most luminous distant sources of light in the submillimeter-wavelength range.
Herschel data, which sees submillimeter and far-infrared light, were then used to home in on the targets.
The results showed that some of the objects were bright, young galaxies that had been gravitationally lensed, and others were clusters of galaxies churning out new stars.
Each of these young objects is seen to be converting gas and dust into stars at a rate of a few hundred to 1,500 times the mass of our Sun per year.
By comparison, our own Milky Way galaxy today is producing stars at an average rate of just one solar mass per year.
While the astronomers have not yet conclusively established the ages and luminosities of many of these newly discovered distant galaxy concentrations, they are the best candidates yet found for galactic proto-clusters.
228 distant object observed by Herschel’s SPIRE instrument. Image credit: N. Aghanim et al.
“Hints of these kinds of objects had been found earlier in data from Herschel and other telescopes, but the all-sky capability of Planck revealed many more candidates for us to study,” said Dr Dole, who is the corresponding author of the paper published in the journal Astronomy & Astrophysics.
“We still have a lot to learn about this new population, requiring further follow-up studies with other observatories. But we believe that they are a missing piece of cosmological structure formation.”
“Even when we combined the powerful capabilities of Planck and Herschel, we were only scratching the surface of the phenomena taking place at this critical era in the history of our Universe, when stars, galaxies and clusters seem to be forming simultaneously,” said co-author Dr George Helou of the California Institute of Technology in Pasadena.
“That’s one of the reasons this finding is exciting. It shows us that there is so much more to be learned.”
“Thanks to this new study, we now hope that Planck will be able to play a major role in research into the large-scale structure of the Universe,” added Prof Gianfranco de Zotti of the International School for Advanced Studies in Trieste, Italy, and the INAF-Astronomical Observatory of Padova.
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