共查询到20条相似文献，搜索用时 312 毫秒
1.
Peter M.W. Kalberla 《Astrophysics and Space Science》2004,289(3-4):239-242
We consider a disk-like dark matter model for the Milky Way andcompare a few predictions with observations. The observed gaseousflaring for HI and molecular gas fits the model predictions indetail. The global HI distribution in the Milky Way needs to beexplained by a multiphase medium. The dark matter distribution in theGalactic halo is traced by a low density component of halogas. High-velocity clouds with distances up to ～ 50 kpc may beexplained as condensations which originate from instabilities withinthe gaseous halo. Our model explains also ‘beards’ and ‘forbiddenvelocities’ as observed in the rotation curves of externalgalaxies. A disk-like dark matter model is self-consistent and inexcellent agreement with observations. 相似文献
2.
Dragan Slavkov Hajdukovic 《Astrophysics and Space Science》2012,337(1):9-14
Recently, the gravitational polarization of the quantum vacuum was proposed as alternative to the dark matter paradigm. In
the present paper we consider four benchmark measurements: the universality of the central surface density of galaxy dark
matter haloes, the cored dark matter haloes in dwarf spheroidal galaxies, the non-existence of dark disks in spiral galaxies
and distribution of dark matter after collision of clusters of galaxies (the Bullet cluster is a famous example). Only some
of these phenomena (but not all of them) can (in principle) be explained by the dark matter and the theories of modified gravity.
However, we argue that the framework of the gravitational polarization of the quantum vacuum allows the understanding of the
totality of these phenomena. 相似文献
3.
Marcel Zemp Jürg Diemand † Michael Kuhlen Piero Madau Ben Moore Doug Potter Joachim Stadel Lawrence Widrow 《Monthly notices of the Royal Astronomical Society》2009,394(2):641-659
We use the recently completed one billion particle Via Lactea II Λ cold dark matter simulation to investigate local properties like density, mean velocity, velocity dispersion, anisotropy, orientation and shape of the velocity dispersion ellipsoid, as well as the structure in velocity space of dark matter haloes. We show that at the same radial distance from the halo centre, these properties can deviate by orders of magnitude from the canonical, spherically averaged values, a variation that can only be partly explained by triaxiality and the presence of subhaloes. The mass density appears smooth in the central relaxed regions but spans four orders of magnitude in the outskirts, both because of the presence of subhaloes as well as of underdense regions and holes in the matter distribution. In the inner regions, the local velocity dispersion ellipsoid is aligned with the shape ellipsoid of the halo. This is not true in the outer parts where the orientation becomes more isotropic. The clumpy structure in local velocity space of the outer halo cannot be well described by a smooth multivariate normal distribution. Via Lactea II also shows the presence of cold streams made visible by their high 6D phase space density. Generally, the structure of dark matter haloes shows a high degree of graininess in phase space that cannot be described by a smooth distribution function. 相似文献
4.
The dark energy model with barotropic equation of state, which interacts with dark matter by gravitation and by other force, which causes the energy-momentum exchange between them, is considered. Both components are described in approximation of ideal fluid, which are parameterized by density, equation of state and effective sound speed parameters. The three types of interactions between dark components are considered: interaction independent from their densities, interaction proportional to energy density of dark energy, and interaction proportional to energy density of dark matter. The equations that describe the expansion dynamics of homogeneous and isotropic Universe and evolution of densities of both components for different values of interaction parameter are obtained on the bases of the general covariant conservation equations and Einstein’s ones. For three kinds of interactions, the existing of the range of values of parameters of dark energy for which the densities of dark components are negative was shown. The conditions of positivity of energy density of dark energy and dark matter were written for which the constraints on the value of parameter of interaction were derived. The dynamics of expansion of the Universe with these interactions of dark energy and dark matter is analyzed. 相似文献
5.
We study nonthermal production of baryon and dark matter. If we extend the MSSM by introducing some singlet chiral superfields so as to enlarge the conserved global symmetry, the abundance of the baryon and the dark matter in the universe may be explained as the charge asymmetry of that symmetry. In such a case, the baryon energy density and the dark matter energy density in the present universe can be correlated each other and take the similar order values naturally. 相似文献
6.
Ravi K. Sheth 《Monthly notices of the Royal Astronomical Society》1998,300(4):1057-1070
A model of the gravitationally evolved dark matter distribution, in the Eulerian space, is developed. It is a simple extension of the excursion set model that is commonly used to estimate the mass function of collapsed dark matter haloes. In addition to describing the evolution of the Eulerian space distribution of the haloes, the model allows one to describe the evolution of the dark matter itself. It can also be used to describe density profiles, on scales larger than the virial radius of these haloes, and to quantify the way in which matter flows in and out of Eulerian cells. When the initial Lagrangian space distribution is white noise Gaussian, the model suggests that the Inverse Gaussian distribution should provide a reasonably good approximation to the evolved Eulerian density field, in agreement with numerical simulations. Application of this model to clustering from more general Gaussian initial conditions is discussed at the end. 相似文献
7.
On the nature of superoutbursts in dwarf novae 总被引：1，自引：0，他引：1
M.R. Truss J.R. Murray G.A. Wynn 《Monthly notices of the Royal Astronomical Society》2001,324(1):L1-L5
We determine a crucial feature of the dark halo density distribution from the fact that the luminous matter dominates the gravitational potential at about one disc scalelength R d , but at the optical edge the dark matter has already become the main component of the galaxy density. From the kinematics of 137 spirals we find that the dark matter halo density profiles are self-similar at least out to R opt and show core radii much larger than the corresponding disc scalelengths. The luminous regions of spirals consist of stellar discs embedded in dark haloes with roughly constant density. This invariant dark matter profile is very difficult to reconcile with the fundamental properties of the density distribution of cold dark matter haloes. With respect to previous work, the present evidence is obtained by means of a robust method and for a large and complete sample of normal spirals. 相似文献
8.
《New Astronomy Reviews》2002,46(12):755-766
An overview is presented of the main properties of dark matter haloes, as we know them from observations, essentially from rotation curves around spiral and dwarf galaxies. Detailed rotation curves are now known for more than a thousand galaxies, revealing that they are not so flat in the outer parts, but rising for late-types, and falling for early-types. A well-established result now is that most bright galaxies are not dominated by dark matter inside their optical disks. Only for dwarfs and LSB (Low Surface Brightness galaxies) dark matter plays a dominant role in the visible regions. The 3D-shape of haloes are investigated through several methods that will be discussed: polar rings, flaring of HI planes, X-ray isophotes. It is not yet possible with rotation curves to know how far haloes extend, but tentatives have been made. It will be shown that the dark matter appears to be coupled to the gas in spirals and dwarfs, suggesting that dark baryons could play a major role in rotation curves. Theories proposing to replace the non-baryonic dark matter by a different dynamical or gravity law, such as MOND, have to take into account the dark baryons, especially since their spatial distribution is likely to be quite different from the visible matter. 相似文献
9.
The data on the peculiar velocities of 1493 RFGC flat spiral galaxies processed using the POTENT method allowed the density distribution of matter, including dark matter, on 75-Mpc scales to be reconstructed. Well-known attractors (the Great Attractor, the Perseus—Pisces and Coma superclusters) and voids are separated from the distribution. In general, the density distribution is close to that of IRAS galaxies, suggesting that the luminous-to-dark matter density ratio is constant. The masses of the main attractors were estimated. 相似文献
10.
Frank C. van den Bosch † Rob A. Swaters 《Monthly notices of the Royal Astronomical Society》2001,325(3):1017-1038
The standard cold dark matter (CDM) model has recently been challenged by the claim that dwarf galaxies have dark matter haloes with constant-density cores, whereas CDM predicts haloes with steeply cusped density distributions. Consequently, numerous alternative dark matter candidates have recently been proposed. In this paper we scrutinize the observational evidence for the incongruity between dwarf galaxies and the CDM model. To this end, we analyse the rotation curves of 20 late-type dwarf galaxies studied by Swaters. Taking the effects of beam smearing and adiabatic contraction into account, we fit mass models to these rotation curves with dark matter haloes with different cusp slopes, ranging from constant-density cores to r −2 cusps. Even though the effects of beam smearing are small for these data, the uncertainties in the stellar mass-to-light ratio and the limited spatial sampling of the halo's density distribution hamper a unique mass decomposition. Consequently, the rotation curves in our sample cannot be used to discriminate between dark haloes with constant-density cores and r −1 cusps. We show that the dwarf galaxies analysed here are consistent with CDM haloes in a ΛCDM cosmology, and that there is thus no need to abandon the idea that dark matter is cold and collisionless. However, the data are also consistent with any alternative dark matter model that produces dark matter haloes with central cusps less steep than r −1.5 . In fact, we argue that based on existing H i rotation curves alone, at best weak limits can be obtained on cosmological parameters and/or the nature of the dark matter. In order to make progress, rotation curves with higher spatial resolution and independent measurements of the mass-to-light ratio of the disc are required. 相似文献
11.
V. Majerník 《Astrophysics and Space Science》1996,240(1):133-139
Using the heuristic arguments of quantum physics we describe a new mechanism of the creation of short-living particles from the virtual ones in a stationary gravitation field. The mass of these particles is a function of the intensity of gravitation field. We suppose that the particles created in the gravitation field form a part of the non-baryonic dark matter. Having the intensity of gravitation field in a galaxy we can calculate the density of dark matter created in it by the vacuum quantum fluctuation. We calculate the distribution of this dark matter in a model galaxy and show that its total mass is comparable with the visible mass of the galaxy. 相似文献
12.
《天文和天体物理学研究(英文版)》2017,(7)
Recently, a very strong correlation between the central surface density of stars and dynamical mass in 135 disk galaxies has been obtained. It has been shown that this central-surface-densities relation agrees very well with Modified Newtonian Dynamics(MOND). In this article, we show that if we assume the baryons have an isothermal distribution and dark matter exists, then it is possible to derive by means of the Jeans equation an analytic central-surface-densities relation connecting dark matter and baryons that agrees with the observed relation. We find that the observed central-surface-densities relation can also be accommodated in the context of dark matter provided the latter is described by an isothermal profile. Therefore, the observed relation is consistent with not only MOND. 相似文献
13.
R. I. Hynes K. O'' Brien F. Mullally T. Ashcraft 《Monthly notices of the Royal Astronomical Society》2009,399(1):281-286
Caustics are a generic feature of the non-linear growth of structure in the dark matter distribution. If the dark matter were absolutely cold, its mass density would diverge at caustics, and the integrated annihilation probability would also diverge for individual particles participating in them. For realistic dark matter candidates, this behaviour is regularized by small but non-zero initial thermal velocities. We present a mathematical treatment of evolution from hot, warm or cold dark matter initial conditions which can be directly implemented in cosmological N -body codes. It allows the identification of caustics and the estimation of their annihilation radiation in fully general simulations of structure formation. 相似文献
14.
Pat Scott Malcolm Fairbairn Joakim Edsjö 《Monthly notices of the Royal Astronomical Society》2009,394(1):82-104
In regions of very high dark matter density such as the Galactic Centre, the capture and annihilation of WIMP dark matter by stars has the potential to significantly alter their evolution. We describe the dark stellar evolution code D ark S tars , and present a series of detailed grids of WIMP-influenced stellar models for main-sequence stars. We describe the changes in stellar structure and main-sequence evolution which occur as a function of the rate of energy injection by WIMPs, for masses of 0.3–2.0 M⊙ and metallicities Z = 0.0003–0.02 . We show what rates of energy injection can be obtained using realistic orbital parameters for stars at the Galactic Centre, including detailed consideration of the velocity and density profiles of dark matter. Capture and annihilation rates are strongly boosted when stars follow elliptical rather than circular orbits. If there is a spike of dark matter induced by the supermassive black hole at the Galactic Centre, single solar mass stars following orbits with periods as long as 50 yr and eccentricities as low as 0.9 could be significantly affected. Binary systems with similar periods about the Galactic Centre could be affected on even less eccentric orbits. The most striking observational effect of this scenario would be the existence of a binary consisting of a low-mass protostar and a higher mass evolved star. The observation of low-mass stars and/or binaries on such orbits would either provide a detection of WIMP dark matter, or place stringent limits on the combination of the WIMP mass, spin-dependent nuclear-scattering cross-section, halo density and velocity distribution near the Galactic Centre. In some cases, the derived limits on the WIMP mass and spin-dependent nuclear-scattering cross-section would be of comparable sensitivity to current direct-detection experiments. 相似文献
15.
An upper limit to the amplitude of the overall density fluctuation has been found by means of the gravitational lensing effect of the density inhomogeneity on the luminosities of quasars with larger redshifts. The observed differences of luminosities of quasars located at different directions are partially given by the lensing effect, therefore, a useful upper limit to the inhomogeneity can be derived if the luminosity distribution of quasars is uniform enough. We obtain that, in the case of the density parameter of the Universe =1, the overall matter should be less clustered than the luminous matter by a factor of at least 3. This result may not favour the biased dark matter scenario for the formation of large-scale structure in the Universe. 相似文献
16.
Y. Ascasibar P. Jean C. B&#;hm † J. Knödlseder 《Monthly notices of the Royal Astronomical Society》2006,368(4):1695-1705
About one year ago, it was speculated that decaying or annihilating light dark matter (LDM) particles could explain the flux and extension of the 511-keV line emission in the Galactic Centre. Here, we present a thorough comparison between theoretical expectations of the Galactic positron distribution within the LDM scenario and observational data from INTEGRAL /SPI. Unlike previous analyses, there is now enough statistical evidence to put tight constraints on the shape of the dark matter (DM) halo of our Galaxy, if the Galactic positrons originate from DM. For annihilating candidates, the best fit to the observed 511-keV emission is provided by a radial density profile with inner logarithmic slope γ= 1.03 ± 0.04 . In contrast, decaying DM requires a much steeper density profile, γ > 1.5 , rather disfavoured by both observations and numerical simulations. Within the annihilating LDM scenario, a velocity-independent cross-section would be consistent with the observational data while a cross-section purely proportional to v 2 can be rejected at a high confidence level. Assuming the most simplistic model where the Galactic positrons are produced as primaries, we show that the LDM candidate should be a scalar rather than a spin-1/2 particle and obtain a very stringent constraint on the value of the positron production cross-section to explain the 511-keV emission. One consequence is that the value of the fine structure constant α should differ from that recommended in the CODATA (Committee on Data for Science and Technology). This is a very strong test for the LDM scenario and an additional motivation in favour of experiments measuring α directly. Our results finally indicate that an accurate measurement of the shape of the dark halo profile could have a tremendous impact on the determination of the origin of the 511-keV line and vice versa. 相似文献
17.
R. Sadat 《Astrophysics and Space Science》1995,234(2):303-323
In this paper a family of two-component non-isothermal hydrostatic models are elaborated in order to simulate clusters of galaxies in which a dark background exists. The influence of an invisible component on the dynamical analysis is examined. We show that the mass-to-light ratio MLR is not linearly related to the actual amount of the unseen mass, leading to the conclusion that the MLR is not a reliable indicator of the amount of dark matter in clusters of galaxies. The determination of the mass depends strongly on the relative concentration of both the luminous and the dark component. This is the so-called Limber effect which is quantified on the ground of our two-component hydrostatic models. The asymptotic behaviour of the density profile of both components is investigated. We found that they allow useful information to be obtained on the distribution of the unseen component and on its thermodynamical state. We also show that intra-cluster medium (ICM) can not mimic the dark matter and consequently one has to invoke the dark matter to explain the high MLRs in galaxy clusters. 相似文献
18.
Silvia Pellegrini Luca Ciotti 《Monthly notices of the Royal Astronomical Society》2006,370(4):1797-1803
NGC 3379 is a well-studied nearby elliptical for which optical investigations have claimed a little dark matter content, or even no dark matter. Recently, its total mass profile M ( r ) has been derived by exploiting Chandra observations of its extended and X-ray emitting interstellar medium, based on the hypothesis of hydrostatic equilibrium for the hot gas. The resulting total mass within the effective radius R e has been claimed to be a few times larger than that found by optical studies. Here, we show that part of the discrepancy can be due to an underestimate of the optically derived mass, and the remaining discrepancy of a factor of ∼2 can be explained by deviations from hydrostatic equilibrium of the hot gas. By using hydrodynamical simulations tailored to reproduce the observed hot gas properties of NGC 3379, and by assuming as input for the simulations the total mass profile derived optically, we show that (i) the hot gas at the present time has X-ray properties consistent with those observed only if it is outflowing over most of the galactic body, and (ii) an overestimate of M of the same size found in the recent X-ray analysis is recovered when assuming hydrostatic equilibrium. We also show that the hot gas is outflowing even for a dark matter fraction within R e as large as derived with the standard X-ray procedure based on the hydrostatic equilibrium assumption, which shows the unapplicability of the method for this galaxy. Finally, we find that the whole range of dark mass amount and distribution allowed for by optical studies is compatible with a hot gas flow with the observed X-ray properties. 相似文献
19.
20.
Carlo Giocoli Lidia Pieri Giuseppe Tormen 《Monthly notices of the Royal Astronomical Society》2008,387(2):689-697
In the standard model of cosmic structure formation, dark matter haloes form by gravitational instability. The process is hierarchical: smaller systems collapse earlier, and later merge to form larger haloes. The galaxy clusters, hosted by the largest dark matter haloes, are at the top of this hierarchy and representing the largest as well as the last structures formed in the Universe, while the smaller and first haloes are those Earth-sized dark subhaloes that have been both predicted by theoretical considerations and found in numerical simulations, though there do not exist any observational hints of their existence. The probability that a halo of mass m at redshift z will be part of a larger halo of mass M at the present time can be described in the frame of the extended Press & Schecter theory making use of the progenitor (conditional) mass function. Using the progenitor mass function, we calculate analytically, at redshift zero, the distribution of subhaloes in mass, formation epoch and rarity of the peak of the density field at the formation epoch. That is done for a Milky Way size system, assuming both a spherical and an ellipsoidal collapse model. Our calculation assumes that small progenitors do not lose mass due to dynamical processes after entering the parent halo, and that they do not interact with other subhaloes. For a Λ cold dark matter power spectrum, we obtain a subhalo mass function d n /d m proportional to m −α with a model-independent α∼ 2 . Assuming that the dark matter is a weakly interacting massive particle, the inferred distributions are used to test the feasibility of an indirect detection in the γ-ray energy band of such a population of subhaloes with a Gamma-ray Large Area Space Telescope like satellite. 相似文献