390 research outputs found

### Morphological Statistics of the Cosmic Web

We report the {\em first} systematic study of the supercluster-void network
in the $\Lambda$CDM concordance cosmology treating voids and superclusters on
an equal footing. We study the dark matter density field in real space smoothed
with the $L_s = 5$ \hm1 Mpc Gaussian window. Superclusters and voids are
defined as individual members of over-dense and under-dense excursion sets
respectively. We determine the morphological properties of the cosmic web at a
large number of dark matter density levels by computing Minkowski functionals
for every supercluster and void. At the adopted smoothing scale individual
superclusters totally occupy no more than about 5% of the total volume and
contain no more than 20% of mass if the largest supercluster is excluded.
Likewise, individual voids totally occupy no more than 14% of volume and
contain no more than 4% of mass if the largest void is excluded.
The genus of individual superclusters can be $\sim 5$ while the genus of
individual voids reaches $\sim 55$, implying significant amount of substructure
in superclusters and especially in voids. Large voids are typically distinctly
non-spherical.Comment: 6 pages, 4 figures, uses iaus.cls, Invited talk at IAU Colloquium 195
"Outskirts of galaxy clusters: intense life in the suburbs", Torino, Italy,
March 12-16, 200

### Tessellating the Universe: the Zel'dovich and Adhesion tiling of space

The adhesion approximation is a simple analytical model suggested for
explanation of the major geometrical features of the observed structure in the
galaxy distribution on scales from 1 to (a few)x100/h Mpc. It is based on
Burgers' equation and therefore allows analysis in considerable detail. A
particular version of the model that assumes the infinitesimal viscosity
naturally results in irregular tessellation of the universe. Generic elements
of the tessellation: vertices, edges, faces and three-dimensional tiles can be
associated with astronomical objects of different kinds: clusters,
superclusters and voids of galaxies. Point-like vertices contain the most of
the mass and one-dimensional edges (filaments) are the second massive elements.
The least massive are the two-dimensional faces and tiles (voids). The
evolution of the large-scale structure can be viewed as a continuous process
that transports mass predominantly from the high- to low-dimensional elements
of the tessellation. For instance, the mass from the cells flows into faces,
edges and vertices, in turn the mass from faces flows into edges and vertices,
etc. At the same time, the elements of the tessellation themselves are in
continuous motion resulting in mergers of some vertices, growth of some tiles
and shrinking and disappearance of the others as well as other metamorphoses.Comment: 18 pages, 11 figure

### Universality of the Network and Bubble Topology in Cosmological Gravitational Simulations

Using percolation statistics we, for the first time, demonstrate the
universal character of a network pattern in the real space, mass distributions
resulting from nonlinear gravitational instability of initial Gaussian
fluctuations. Percolation analysis of five stages of the nonlinear evolution of
five power law models reveals that all models show a shift toward a network
topology if seen with high enough resolution. However, quantitatively, the
shift is significantly different in different models: the smaller the spectral
index ,n, the stronger the shift. On the contrary, the shift toward the
"bubble" topology is characteristic only for the n <= -1 models. We find that
the mean density of the percolating structures in the nonlinear density
distributions generally is very different from the density threshold used to
identify them and corresponds much better to a visual impression. We also find
that the maximum of the number of structures (connected regions above or below
a specified density threshold) in the evolved, nonlinear distributions is
always smaller than in Gaussian fields with the same spectrum, and is
determined by the effective slope at the cutoff frequency.Comment: The paper is 26 pages long. The latex file uses aasms.sty as a style
file. There are 5 figures and 2 tables included

### Dark matter caustics and the enhancement of self-annihilation flux

Cold dark matter haloes are populated by caustics, which are yet to be
resolved in N-body simulations or observed in the Universe. Secondary infall
model provides a paradigm for the study of caustics in "typical" haloes
assuming that they have had no major mergers and have grown only by smooth
accretion. This is a particular characteristic of the smallest dark matter
haloes of about 10^{-5} Mo, which although "atypical" contain no substructures
and could have survived until now with no major mergers. Thus using this model
as the first guidline, we evaluate the neutralino self-annihilation flux for
these haloes. Our results show that caustics could leave a distinct sawteeth
signature on the differential and cumulative fluxes coming from the outer
regions of these haloes. The total annihilation signal from the regions away
from the centre can be boosted by about forty percents.Comment: To appear in JCAP, 4 pages, 3 figure

- …