Dark matter map of KiDS survey region (region G12)
Dark matter map of KiDS survey region (region G9)
Dark matter map of KiDS survey region (region G15)
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Careful study of large area of sky imaged by VST reveals intriguing result
Analysis of a giant new galaxy survey,
made with ESO’s VLT Survey Telescope in Chile, suggests that dark matter
may be less dense and more smoothly distributed throughout space than
previously thought. An international team used data from the Kilo Degree
Survey (KiDS) to study how the light from about 15 million distant
galaxies was affected by the gravitational influence of matter on the
largest scales in the Universe. The results appear to be in disagreement
with earlier results from the Planck satellite.
Hendrik Hildebrandt from the Argelander-Institut für Astronomie in Bonn, Germany and Massimo Viola from the Leiden Observatory in the Netherlands led a team of astronomers [1] from institutions around the world who processed images from the Kilo Degree Survey (KiDS), which was made with ESO’s VLT Survey Telescope
(VST) in Chile. For their analysis, they used images from the survey
that covered five patches of the sky covering a total area of around
2200 times the size of the full Moon [2], and containing around 15 million galaxies.
By exploiting the exquisite image quality available to the VST at the
Paranal site, and using innovative computer software, the team were
able to carry out one of the most precise measurements ever made of an
effect known as cosmic shear. This is a subtle variant of weak gravitational lensing,
in which the light emitted from distant galaxies is slightly warped by
the gravitational effect of large amounts of matter, such as galaxy clusters.
In cosmic shear, it is not galaxy clusters but large-scale structures
in the Universe that warp the light, which produces an even smaller
effect. Very wide and deep surveys, such as KiDS, are needed to ensure
that the very weak cosmic shear signal is strong enough to be measured
and can be used by astronomers to map the distribution of gravitating
matter. This study takes in the largest total area of the sky to ever be
mapped with this technique so far.
Intriguingly, the results of their analysis appear to be inconsistent with deductions from the results of the European Space Agency’s Planck satellite,
the leading space mission probing the fundamental properties of the
Universe. In particular, the KiDS team’s measurement of how clumpy
matter is throughout the Universe — a key cosmological parameter — is significantly lower than the value derived from the Planck data [3].
Massimo Viola explains: “This latest result indicates that dark
matter in the cosmic web, which accounts for about one-quarter of the
content of the Universe, is less clumpy than we previously believed.”
Dark matter remains elusive to detection, its presence only
inferred from its gravitational effects. Studies like these are the
best current way to determine the shape, scale and distribution of this
invisible material.
The surprise result of this study also has implications for our wider understanding of the Universe, and how it has evolved
during its almost 14-billion-year history. Such an apparent
disagreement with previously established results from Planck means that
astronomers may now have to reformulate their understanding of some
fundamental aspects of the development of the Universe.
Hendrik Hildebrandt comments: “Our findings will help to refine our theoretical models of how the Universe has grown from its inception up to the present day.”
The KiDS analysis of data from the VST is an important step
but future telescopes are expected to take even wider and deeper
surveys of the sky.
The co-leader of the study, Catherine Heymans of the University of Edinburgh in the UK adds: “Unravelling
what has happened since the Big Bang is a complex challenge, but by
continuing to study the distant skies, we can build a picture of how our
modern Universe has evolved.”
“We see an intriguing discrepancy with Planck cosmology at the
moment. Future missions such as the Euclid satellite and the Large
Synoptic Survey Telescope will allow us to repeat these measurements and
better understand what the Universe is really telling us,” concludes Konrad Kuijken (Leiden Observatory, the Netherlands), who is principal investigator of the KiDS survey.
Notes
[1] The international KiDS team of researchers includes scientists from Germany, the Netherlands, the UK, Australia, Italy, Malta and Canada.
[3] The parameter measured is called S8.
Its value is a combination of the size of density fluctuations in, and
the average density of, a section of the Universe. Large fluctuations in
lower density parts of the Universe have an effect similar to that of
smaller amplitude fluctuations in denser regions and the two cannot be
distinguished by observations of weak lensing. The 8 refers to a cell
size of 8 megaparsecs, which is used by convention in such studies.
More Information
This research was presented in the paper entitled
“KiDS-450: Cosmological parameter constraints from tomographic weak
gravitational lensing”, by H. Hildebrandt et al., to appear in Monthly Notices of the Royal Astronomical Society.
The team is composed of H. Hildebrandt (Argelander-Institut
für Astronomie, Bonn, Germany), M. Viola (Leiden Observatory, Leiden
University, Leiden, the Netherlands), C. Heymans (Institute for
Astronomy, University of Edinburgh, Edinburgh, UK), S. Joudaki (Centre
for Astrophysics & Supercomputing, Swinburne University of
Technology, Hawthorn, Australia), K. Kuijken (Leiden Observatory, Leiden
University, Leiden, the Netherlands), C. Blake (Centre for Astrophysics
& Supercomputing, Swinburne University of Technology, Hawthorn,
Australia), T. Erben (Argelander-Institut für Astronomie, Bonn,
Germany), B. Joachimi (University College London, London, UK), D Klaes
(Argelander-Institut für Astronomie, Bonn, Germany), L. Miller
(Department of Physics, University of Oxford, Oxford, UK), C.B. Morrison
(Argelander-Institut für Astronomie, Bonn, Germany), R. Nakajima
(Argelander-Institut für Astronomie, Bonn, Germany), G. Verdoes Kleijn
(Kapteyn Astronomical Institute, University of Groningen, Groningen, the
Netherlands), A. Amon (Institute for Astronomy, University of
Edinburgh, Edinburgh, UK), A. Choi (Institute for Astronomy, University
of Edinburgh, Edinburgh, UK), G. Covone (Department of Physics,
University of Napoli Federico II, Napoli, Italy), J.T.A. de Jong (Leiden
Observatory, Leiden University, Leiden, the Netherlands), A. Dvornik
(Leiden Observatory, Leiden University, Leiden, the Netherlands), I.
Fenech Conti (Institute of Space Sciences and Astronomy (ISSA),
University of Malta, Msida, Malta; Department of Physics, University of
Malta, Msida, Malta), A. Grado (INAF – Osservatorio Astronomico di
Capodimonte, Napoli, Italy), J. Harnois-Déraps (Institute for Astronomy,
University of Edinburgh, Edinburgh, UK; Department of Physics and
Astronomy, University of British Columbia, Vancouver, Canada), R.
Herbonnet (Leiden Observatory, Leiden University, Leiden, the
Netherlands), H. Hoekstra (Leiden Observatory, Leiden University,
Leiden, the Netherlands), F. Köhlinger (Leiden Observatory, Leiden
University, Leiden, the Netherlands), J. McFarland (Kapteyn Astronomical
Institute, University of Groningen, Groningen, the Netherlands), A.
Mead (Department of Physics and Astronomy, University of British
Columbia, Vancouver, Canada), J. Merten (Department of Physics,
University of Oxford, Oxford, UK), N. Napolitano (INAF – Osservatorio
Astronomico di Capodimonte, Napoli, Italy), J.A. Peacock (Institute for
Astronomy, University of Edinburgh, Edinburgh, UK), M. Radovich (INAF –
Osservatorio Astronomico di Padova, Padova, Italy), P. Schneider
(Argelander-Institut für Astronomie, Bonn, Germany), P. Simon
(Argelander-Institut für Astronomie, Bonn, Germany), E.A. Valentijn
(Kapteyn Astronomical Institute, University of Groningen, Groningen, the
Netherlands), J.L. van den Busch (Argelander-Institut für Astronomie,
Bonn, Germany), E. van Uitert (University College London, London, UK)
and L. van Waerbeke (Department of Physics and Astronomy, University of
British Columbia, Vancouver, Canada).
ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive ground-based astronomical
observatory by far. It is supported by 16 countries: Austria, Belgium,
Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy,
the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the
United Kingdom, along with the host state of Chile. ESO carries out an
ambitious programme focused on the design, construction and operation of
powerful ground-based observing facilities enabling astronomers to make
important scientific discoveries. ESO also plays a leading role in
promoting and organising cooperation in astronomical research. ESO
operates three unique world-class observing sites in Chile: La Silla,
Paranal and Chajnantor. At Paranal, ESO operates the Very Large
Telescope, the world’s most advanced visible-light astronomical
observatory and two survey telescopes. VISTA works in the infrared and
is the world’s largest survey telescope and the VLT Survey Telescope is
the largest telescope designed to exclusively survey the skies in
visible light. ESO is a major partner in ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre European Extremely Large Telescope, the E-ELT,
which will become “the world’s biggest eye on the sky”.
Links
Contacts
Hendrik Hildebrandt
Argelander-Institut für Astronomie
Bonn, Germany
Tel: +49 228 73 1772
Email: hendrik@astro.uni-bonn.de
Argelander-Institut für Astronomie
Bonn, Germany
Tel: +49 228 73 1772
Email: hendrik@astro.uni-bonn.de
Massimo Viola
Leiden Observatory
Leiden, The Netherlands
Tel: +31 (0)71 527 8442
Email: viola@strw.leidenuniv.nl
Leiden Observatory
Leiden, The Netherlands
Tel: +31 (0)71 527 8442
Email: viola@strw.leidenuniv.nl
Catherine Heymans
Institute for Astronomy, University of Edinburgh
Edinburgh, United Kingdom
Tel: +44 131 668 8301
Email: heymans@roe.ac.uk
Institute for Astronomy, University of Edinburgh
Edinburgh, United Kingdom
Tel: +44 131 668 8301
Email: heymans@roe.ac.uk
Konrad Kuijken
Leiden Observatory
Leiden, The Netherlands
Tel: +31 715275848
Cell: +31 628956539
Email: kuijken@strw.leidenuniv.nl
Leiden Observatory
Leiden, The Netherlands
Tel: +31 715275848
Cell: +31 628956539
Email: kuijken@strw.leidenuniv.nl
Richard Hook
ESO Public Information Officer
Garching bei Munchen, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
ESO Public Information Officer
Garching bei Munchen, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
