Wojtak, R., Łokas, E. L., Mamon, G. A., Gottlöber, S., Klypin, A., Hoffman, Y., 2008, Monthly Notices of the Royal Astronomical Society
, 388, 2 , 815 Published: August 2008
We study the distribution function (DF) of dark matter particles in haloes of mass range 1014-1015Msolar. In the numerical part of this work we measure the DF for a sample of relaxed haloes formed in the simulation of a standard Λ cold dark matter (ΛCDM) model. The DF is expressed as a function of energy E and the absolute value of the angular momentum L, a form suitable for comparison with theoretical models. By proper scaling we obtain the results that do not depend on the virial mass of the haloes. We demonstrate that the DF can be separated into energy and angular momentum components and propose a phenomenological model of the DF in the form . This formulation involves three parameters describing the anisotropy profile in terms of its asymptotic values (β0 and β∞) and the scale of transition between them (L0). The energy part fE(E) is obtained via inversion of the integral for spatial density. We provide a straightforward numerical scheme for this procedure as well as a simple analytical approximation for a typical halo formed in the simulation. The DF model is extensively compared with the simulations: using the model parameters obtained from fitting the anisotropy profile, we recover the DF from the simulation as well as the profiles of the dispersion and kurtosis of radial and tangential velocities. Finally, we show that our DF model reproduces the power-law behaviour of phase-space density Q = ρ(r)/σ3(r).
Hoffman, Y., Martinez-Vaquero, L. A., Yepes, G., Gottlöber, S., 2008, Monthly Notices of the Royal Astronomical Society
, 386, 1 , 390 Published: May 2008
To study the local Hubble flow, we have run constrained dark matter (DM) simulations of the Local Group (LG) in the concordance Λ cold dark matter (CDM) and open cold dark matter (OCDM) cosmologies, with identical cosmological parameters apart from the Λ term. The simulations were performed within a computational box of centred on the LG. The initial conditions were constrained by the observed peculiar velocities of galaxies and positions of X-ray nearby clusters of galaxies. The simulations faithfully reproduce the nearby large-scale structure, and in particular the Local Supercluster and the Virgo cluster. LG-like objects have been selected from the DM haloes so as to closely resemble the dynamical properties of the LG. Both the ΛCDM and OCDM simulations show very similar local Hubble flow around the LG-like objects. It follows that, contrary to recent statements, the dark energy (DE) does not manifest itself in the local dynamics.
Knebe, A., Draganova, N., Power, C., Yepes, G., Hoffman, Y., Gottlöber, S., Gibson, B. K., 2008, Monthly Notices of the Royal Astronomical Society
, 386, 1 , L52 Published: May 2008
We explore the dependence of the radial alignment of subhaloes on the mass of the host halo they orbit in. As the effect is seen on a broad range of scales including massive clusters as well as galactic systems it only appears natural to explore this phenomenon by means of cosmological simulations covering the same range in masses. We have 25 well resolved host dark matter haloes at our disposal ranging from 1015h-1Msolar down to 1012h-1Msolar each consisting of order of a couple of million particles within the virial radius. We observe that subhaloes tend to be more spherical than isolated objects. Both the distributions of sphericity and triaxiality of subhaloes are Gaussian-distributed with peak values of <s> ~ 0.80 and <T> ~ 0.56, irrespective of host mass. Interestingly, we note that the radial alignment is independent of host halo mass and the distribution of cosθ (i.e. the angle between the major-axis Ea of each subhalo and the radius vector of the subhalo in the reference frame of the host) is well fitted by a simple power law P(cosθ) ~ cos4θ with the same fitting parameters for all host haloes.
We present cosmological simulations that closely mimic the real uiverse within ~100 Mpc of the Local Group. The simulations, called constrained simulations, reproduce the large-scale density field with major nearby structures, including the Local Group, the Coma and Virgo Clusters, the Great Attractor, the Perseus-Pisces Supercluster, and the Local Supercluster, in approximately correct locations. The MARK III survey of peculiar velocities of the observed structures inside an 80h-1Mpc sphere is used to constrain the initial conditions. Fourier modes on scales larger than a (Gaussian) resolution of ~Rg=5h-1Mpc are dominated by the constraints, while small-scale waves are essentially random. The main aim of this paper is the structure of the Local Supercluster region (LSC; ~30h-1Mpc around the Virgo Cluster) and the Local Group environment. We find that at the current epoch most of the mass (~7.5×1014h-1Msolar) of the LSC is located in a filament roughly centered on the Virgo Cluster and extending over ~40h-1Mpc. The simulated Local Group (LG) is located in an adjacent smaller filament, which is not a part of the main body of the LSC and has a peculiar velocity of ~250 km s-1 toward the Virgo Cluster. The peculiar velocity field in the LSC region is complicated and is drastically different from the field assumed in the Virgocentric infall models. We find that the peculiar velocity flow in the vicinity of the LG in the simulation is relatively ``cold'': the peculiar line-of-sight velocity dispersion within 7h-1Mpc of the LG is <~60 km s-1, comparable to the observed velocity dispersion of nearby galaxies.
We present results of gasdynamics+N-body constrained cosmological simulations of the Local Supercluster region (LSC; about 30h-1Mpc around the Virgo cluster), which closely mimic the real universe within 100 Mpc, by imposing constraints from the MARK III catalog of galaxy peculiar velocities. The simulations are used to study the properties and possible observational signatures of intergalactic medium in the LSC region. We find that in agreement with previous unconstrained simulations, ~30% of the gas in this region is in the warm/hot phase at T~105-107 K and ~40% in the diffuse phase at T<105 K in low-density regions. The X-ray emission from the warm/hot gas may represent a small (~5%-10%) but important contribution to the X-ray background observed by the ROSAT All-Sky Survey at energies around 1 keV. The best prospects for detection of the warm/hot intergalactic medium of the LSC located in filaments and in the vicinity of virialized regions of groups and clusters are through absorption in resonant lines of O VII and O VIII in soft X-rays and in the O VI doublet in UV. If intergalactic gas in filaments (ρ/<ρ>~1-10) is enriched to typical metallicities of >~0.05, the column densities of O VI, O VII, and O VIII along a random line of sight near the north Galactic pole, especially near the supergalactic plane, have a significant probability to be in the range detectable by current (FUSE, XMM) and future (Constellation-X) instruments.
