An international team of astronomers using NASA’s Hubble Space Telescope has studied a filament of dark matter in three dimensions for the first time.
This Hubble image shows the massive galaxy cluster MACS J0717.5+3745. The location of the dark matter is revealed in a map of the mass in the cluster and surrounding region, shown here in blue. The filament visibly extends out and to the left of the cluster core (NASA / ESA / Harald Ebeling / University of Hawaii at Manoa / Jean-Paul Kneib / LAM)
The Big Bang theory predicts that variations in the density of matter in the very first moments of the Universe led the bulk of the matter in the cosmos to condense into a web of tangled filaments. This view is supported by computer simulations of cosmic evolution, which suggest that the Universe is structured like a web, with long filaments that connect to each other at the locations of massive galaxy clusters. However, these filaments, although vast, are made mainly of dark matter, which is incredibly difficult to observe.
The first identification of one of these filaments was made earlier this year by another team of scientists. Extending 60 million light-years from MACS J0717.5+3745 (or MACS J0717 for short), one of the most massive galaxy clusters known, the filament is part of the cosmic web that constitutes the large-scale structure of the Universe.
Now, the team has gone further by probing a filament’s structure in 3D. Seeing it in three dimensions eliminates many of the pitfalls that come from studying the flat image of such a structure.
“Filaments of the cosmic web are hugely extended and very diffuse, which makes them extremely difficult to detect, let alone study in 3D,” said Dr Mathilde Jauzac of LAM, France, and University of KwaZulu-Natal, South Africa, lead author of a study to be published in the Monthly Notices of the Royal Astronomical Society (arXiv.org version).
The team has combined images of the region, taken using Hubble, NAOJ’s Subaru Telescope and the Canada-France-Hawaii Telescope, with spectroscopic data on the galaxies within it from the WM Keck Observatory and the Gemini Observatory to produce a complete view of the shape of the filament as it extends out from the galaxy cluster almost along our line of sight.
A model that combined positional and velocity information for all these galaxies was constructed and this then revealed the 3D shape and orientation of the filamentary structure. As a result, the team was able to measure the true properties of this elusive filamentary structure without the uncertainties and biases that come from projecting the structure onto two dimensions, as is common in such analyses.
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Bibliographic information: Mathilde Jauzac et al. 2012. A Weak-Lensing Mass Reconstruction of the Large-Scale Filament Feeding the Massive Galaxy Cluster MACSJ 0717.5+3745. Accepted for publication in MNRAS; arXiv: 1208.4323
