An international team of scientists has unveiled detailed maps of dark matter dynamics in the nearby Universe. The research is published in the Journal of Cosmology and Astroparticle Physics (arXiv.org preprint).
Slice through the celestial equator showing the radial component of the velocity field (in km per second). Blue regions are falling towards us and red regions are flying away from us. Galaxies of the SDSS main galaxy sample are overplotted. In the center of the slice, the infalling dynamics of the Sloan Great Wall, one of the largest structure of the known Universe, can be observed. Image credit: Leclercq et al.
Dark matter is the mysterious substance that makes up roughly a quarter of the Universe.
It is invisible to even the most sensitive astronomical instruments because it does not emit or block light.
“As it does not emit or react to light, its distribution and evolution are not directly observable and have to be inferred,” said lead author Dr. Florent Leclercq, from the Institute of Cosmology and Gravitation at the University of Portsmouth, UK.
Dr. Leclercq and his colleagues from the Technische Universität München, the Institut d’Astrophysique de Paris, the Institut Lagrange de Paris, the University of Illinois at Urbana-Champaign, and the University of Portsmouth analyzed data obtained during 2000-2008 from the Sloan Digital Sky Survey (SDSS).
The SDSS survey has deep multi-color images of one fifth of the sky and spectra for more than 900,000 galaxies.
The team used a set of phase-space analysis tools and built on research from 2015, which reconstructed the initial conditions of the nearby Universe.
Slices through the supergalactic plane, with a thickness of 10 megaparsec/h for galaxies. The fields shown are the density (upper panel), the secondary stream density (middle panel) and the radial velocity (lower panel), as a function of distance and supergalactic longitude L. In the upper panel, some structures of the Local Universe are identified in orange: the Coma cluster, the Ursa-Majoris supercluster, and two farther clusters in the direction of Ursa-Major and Ursa-Major/Coma-Berenices. The Virgo-Boötes-Hercules (VBH) filament is also labeled. In purple, two nearby voids in the directions of Ursa-Major and Coma-Berenices, as well as the Boötes void. The center of superclusters and voids is projected onto the supergalactic plane and denoted as stars. Image credit: Leclercq et al.
“We present a cosmographic analysis of the dark matter distribution and its evolution, referred to as the dark matter phase-space sheet, in the nearby Universe as probed by the SDSS main galaxy sample,” the authors said.
“Our method provides extremely accurate estimates of nearby density and velocity fields, even in regions of low galaxy density.”
“It also measures the number of matter streams, and the deformation and parity reversals of fluid elements, which were previously thought inaccessible using observations.”
“We illustrate the approach by showing the phase-space structure of known objects of the nearby Universe such as the Sloan Great Wall, the Coma cluster and the Boötes void.”
The new dark matter maps cover the Northern Sky up to a distance of two billion light-years.
“Adopting a phase-space approach discloses a wealth of information, which was previously only analyzed in simulations and thought to be inaccessible using observations,” Dr. Leclercq said.
“Accessing this information in galaxy surveys opens up new ways of assessing the validity of theoretical models in light of observations.”
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Florent Leclercq et al. The phase-space structure of nearby dark matter as constrained by the SDSS. JCAP 2017 (6): 049; doi: 10.1088/1475-7516/2017/06/049
