Properties of spherical galaxies and clusters with an NFW density profile     

Ewa L. okas  Gary A. Mamon 《Monthly notices of the Royal Astronomical Society》2001,321(1):155-166

Using the standard dynamical theory of spherical systems, we calculate the properties of spherical galaxies and clusters whose density profiles obey the universal form first obtained in high-resolution cosmological N -body simulations by Navarro, Frenk & White (NFW). We adopt three models for the internal kinematics: isotropic velocities, constant anisotropy and increasingly radial OsipkovMerritt anisotropy. Analytical solutions are found for the radial dependence of the mass, gravitational potential, velocity dispersion, energy and virial ratio and we test their variability with the concentration parameter describing the density profile and amount of velocity anisotropy. We also compute structural parameters, such as half-mass radius, effective radius and various measures of concentration. Finally, we derive projected quantities, the surface mass density and line-of-sight as well as aperture-velocity dispersion, all of which can be directly applied in observational tests of current scenarios of structure formation. On the mass scales of galaxies, if constant mass-to-light is assumed, the NFW surface density profile is found to fit HubbleReynolds laws well. It is also well fitted by Sérsic R ^{1/ m} laws, for     but in a much narrower range of m and with much larger effective radii than are observed. Assuming in turn reasonable values of the effective radius, the mass density profiles imply a mass-to-light ratio that increases outwards at all radii.  相似文献   

Dark matter in elliptical galaxies – I. Is the total mass density profile of the NFW form or even steeper?     

Gary A. Mamon  Ewa L. &#;okas 《Monthly notices of the Royal Astronomical Society》2005,362(1):95-109

Elliptical galaxies are modelled as Sérsic luminosity distributions with density profiles (DPs) for the total mass adopted from the DPs of haloes within dissipationless ΛCDM (cold dark matter) N -body simulations. Ellipticals turn out to be inconsistent with cuspy low-concentration NFW models representing the total mass distribution, neither are they consistent with a steeper −1.5 inner slope, nor with the shallower models proposed by Navarro et al., nor with NFW models 10 times more concentrated than predicted, as deduced from several X-ray observations – the mass models, extrapolated inwards, lead to local mass-to-light ratios that are smaller than the stellar value inside an effective radius ( R _e), and to central aperture velocity dispersions that are much smaller than observed. This conclusion remains true as long as there is no sharp steepening (slope < −2) of the dark matter DPs just inside 0.01 virial radii.
The very low total mass and velocity dispersion produced within R _e by an NFW-like total mass profile suggests that the stellar component should dominate the dark matter component out to at least R _e. It should then be difficult to kinematically constrain the inner slope of the DP of ellipticals. The high-concentration parameters deduced from X-ray observations appear to be a consequence of fitting an NFW model to the total mass DP made up of a stellar component that dominates inside and a dark matter component that dominates outwards.
An appendix gives the virial mass dependence of the concentration parameter, central density and total mass of the Navarro et al. model. In a second appendix are given single integral expressions for the velocity dispersions averaged along the line of sight, in circular apertures and in thin slits, for general luminosity density and mass distributions, with isotropic orbits.  相似文献   

Dark matter distribution in the Draco dwarf from velocity moments     

Ewa L. &#;okas  Gary A. Mamon  Francisco Prada 《Monthly notices of the Royal Astronomical Society》2005,363(3):918-928

If the observed relativistic plasma outflows in astrophysical jets are magnetically collimated and a single-component model is adopted, consisting of a wind-type outflow from a central object, then a problem arises with the inefficiency of magnetic self-collimation to collimate a sizeable portion of the mass and magnetic fluxes in the relativistic outflow from the central object. To solve this dilemma, we have applied the mechanism of magnetic collimation to a two-component model consisting of a relativistic wind-type outflow from a central source and a non-relativistic wind from a surrounding disc. By employing a numerical code for a direct numerical solution of the steady-state problem in the zone of super-fast magnetized flow, which allows us to perform a determination of the flow with shocks, it is shown that in this two-component model it is possible to collimate into cylindrical jets all the mass and magnetic fluxes that are available from the central source. In addition, it is shown that the collimation of the plasma in this system is usually accompanied by the formation of oblique shock fronts. The non-relativistic disc-wind not only plays the role of the jet collimator, but it also induces the formation of shocks as it collides with the initially radial inner relativistic wind and also as the outflow is reflected by the system axis. Another interesting feature of this process of magnetic collimation is a sequence of damped oscillations in the width of the jet.  相似文献   

Bacterial ancient DNA as an indicator of human presence in the past: its correlation with palynological and archaeological data     

Jacek Madeja  Agnieszka Wacnik  Agata Zyga  Elzbieta Stankiewicz  Ewa Wypasek  Witold Guminski  Krystyna Harmata 《第四纪科学杂志》2009,24(4):317-321

Palynological investigation is one of the most important tools for reconstructing past vegetation. Some plants have proved to be relatively sensitive indicators of human activity, but most of them are not specific. In this paper we propose a method which can be used for the verification of phases of anthropogenic impact on vegetation distinguished in pollen diagrams. In this work we adopted the existing molecular methods for tracking bacterial ancient DNA of Bifidobacterium and Bacteroides‐Prevotella (known as human‐ and cow‐specific genetic markers) in palynologically and archaeologically associated sediments. This method can be helpful in determining local human presence, especially in those time periods when pollen analysis has not always been very discriminating (Palaeolithic, Mesolithic) and at sites without archaeological evidence. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Mass modelling of dwarf spheroidal galaxies: the effect of unbound stars from tidal tails and the Milky Way     

Jaros&#;aw Klimentowski  Ewa L. &#;okas  Stelios Kazantzidis  Francisco Prada  Lucio Mayer  Gary A. Mamon 《Monthly notices of the Royal Astronomical Society》2007,378(1):353-368

  相似文献   

The mass and anisotropy profiles of galaxy clusters from the projected phase-space density: testing the method on simulated data     

Rados&#;aw Wojtak  Ewa L. &#;okas  Gary A. Mamon  Stefan Gottlöber 《Monthly notices of the Royal Astronomical Society》2009,399(2):812-821

We present a new method of constraining the mass and velocity anisotropy profiles of galaxy clusters from kinematic data. The method is based on a model of the phase-space density, which allows the anisotropy to vary with radius between two asymptotic values. The characteristic scale of transition between these asymptotes is fixed and tuned to a typical anisotropy profile resulting from cosmological simulations. The model is parametrized by two values of anisotropy, at the centre of the cluster and at infinity, and two parameters of the NFW density profile, the scale radius and the scale mass. In order to test the performance of the method in reconstructing the true cluster parameters, we analyse mock kinematic data for 20 relaxed galaxy clusters generated from a cosmological simulation of the standard Λ cold dark matter model. We use Bayesian methods of inference and the analysis is carried out following the Markov Chain Monte Carlo approach. The parameters of the mass profile are reproduced quite well, but we note that the mass is typically underestimated by 15 per cent, probably due to the presence of small velocity substructures. The constraints on the anisotropy profile for a single cluster are in general barely conclusive. Although the central asymptotic value is determined accurately, the outer one is subject to significant systematic errors caused by substructures at large clustercentric distance. The anisotropy profile is much better constrained if one performs joint analysis of at least a few clusters. In this case, it is possible to reproduce the radial variation of the anisotropy over two decades in radius inside the virial sphere.  相似文献   

The distribution function of dark matter in massive haloes     

Rados&#;aw Wojtak  Ewa L. &#;okas  Gary A. Mamon  Stefan Gottlöber  Anatoly Klypin  Yehuda Hoffman 《Monthly notices of the Royal Astronomical Society》2008,388(2):815-828

We study the distribution function (DF) of dark matter particles in haloes of mass range  10¹⁴–10¹⁵ M_⊙  . 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 ( L ₀). The energy part   f _E ( 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 )  .  相似文献   

Long-term variability of occurrence of precipitation forms in winter in Kraków, Poland   总被引：1，自引：0，他引：1  

Robert Twardosz  Ewa ?upikasza  Tadeusz Nied?wied?  Adam Walanus 《Climatic change》2012,113(3-4):623-638

The paper discusses long-term change in snowfall, rainfall and mixed precipitation viewed in conjunction with air temperature and North Atlantic Oscillation (NAO) in winter (December–February). In the study of contemporary climate change and its effect on the hydrological cycle it is useful to focus on winter precipitation forms. A 146-year secular observation series from Kraków, spanning the period 1863–2008, was used to extract data on the number of days with precipitation and on precipitation amount broken down by form. Statistically significant trends were found in total and mixed precipitation, but not in snowfall and rainfall. The climate warming effect has contributed to a material decrease in the snowfall to total winter precipitation ratio during the second half of the 20th c. The highest impact of air temperature was found in the wintertime variation in number of days with snowfall while the NAO had a significant influence on the frequency and amount of both rainfall and snowfall.  相似文献   

Radial hypothesis     

Ewa Rydzyńska 《Astrophysics and Space Science》1987,133(1):183-187

The axial ratio distribution for a sample of SBc galaxies deviates from a flat distribution in ways that are consistent with predictions of the projection effect model for barred spiral galaxies. The axial ratio distribution for a corresponding sample of non-barred Sc galaxies is shown to have, bin for bin, a reciprocal set of deviations from a flat distribution. When the two samples are combined, the deviations counterbalance each other and a nearly flat axial ratio distribution is recovered. This latter result is also consistent with predictions of the projection effect model.  相似文献   

Aspects of the Clay/Electrolyte/Water System with Special Reference to the Geotechnical Properties of Clays     

Ewa T. St  epkowska 《Engineering Geology》1990,28(3-4):249-267

The solid phase of the clay/electrolyte/water system is composed of platy clay particles (of variable thickness, δ, and variable specific surface, S) and of crystal phase (hygroscopic) water, wherefrom δ and S may be estimated. Diffuse layer water between parallel particles and other structural elements at the mutual distance 2d, W_d = d S ρ_w, and macropore water form the liquid phase. Particles are arranged in domains and and clusters, these in aggregates in an “aggregate lattice” with vacancies (macropores) and further superstructures are formed. Contact bonds may develop and long-range forces exist between structural elements, which govern the clay geotechnical behaviour. Cohesion is usually due to van der Waals attraction, friction component–to contact bonds and particle delamination, swelling and suction–to diffuse layer repulsion. Most phenomena may be explained in terms of the equilibrium condition between attraction and repulsion. Heat dissipation must be considered in mechanical processes. The angle of effective stress env envelope is correlated with particle thickness, thus therefrom clay strength may be estimated.  相似文献