共查询到20条相似文献，搜索用时 31 毫秒
1.
《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
2.
In this paper, it is pointed out that if the spiral galaxy revolves about some common centre as a whole, the rotation curve will be changed by the kinematic effects. The common centre could be the centre of supercluster or the centre of dark matter and luminous matter.The kinematic effects on rotation curve are calculated. The additional velocity caused by revolving about the common centre is obtained. In case the direction of revolution is opposite (or consistent) to the direction of rotation, then in the outer region of nucleus, a flat rotation curve could be changed to a constant negative (or postive) gradient. The 44 rotation curves of Sb and Sc galaxies are expressed by means of linear least-squares fit, from which the period of revolving and the ratio of tidal force to self-gravitating force are calculated for every galaxy in extreme cases. The periods for most galaxies are in the reasonable region about 109 years. The tidal force is always less than gravitating force, so the system could be maintained in such a revolving cases. At last, rotation curves in all directions of disk are suggested to pick out the kinematic effects from pure rotation.Work supported by the National Science Foundation of China, under Grant No. 1860610. 相似文献
3.
We consider the effects of projection, internal absorption, and gas-or stellar-velocity dispersion on the measured rotation curves of galaxies with edge-on disks. Axisymmetric disk models clearly show that the rotational velocity in the inner galaxy is highly underestimated. As a result, an extended portion that imitates nearly rigid rotation appears. At galactocentric distances where the absorption is low (i.e., it does not exceed 0.3–0.5m kpc?1), the line profiles can have two peaks, and a rotation curve with minimum distortions can be obtained by estimating the position of the peak that corresponds to a higher rotational velocity. However, the high-velocity peak disappears in high-absorption regions and the actual shape of the rotation curve cannot be reproduced from line-of-sight velocity estimates. In general, the optical rotation curves for edge-on galaxies are of little use in reconstructing the mass distribution in the inner regions, particularly for galaxies with a steep velocity gradient in the central region. In this case, estimating the rotation velocities for outer (transparent) disk regions yields correct results. 相似文献
4.
E. V. Volkov 《Astrophysics》2004,47(3):335-342
The limitations imposed by the shear instability on the formation of gigantic molecular clouds in the central regions of spiral galaxies are examined. The criteria obtained here are illustrated using the example of six galaxies for which the detailed rotation curves are known. The different mechanisms for formation of molecular clouds which apply in the central and edge regions of disk galaxies are evaluated. 相似文献
5.
Wilbur K. Brown 《Astrophysics and Space Science》1984,105(1):109-130
Initial conditions are derived from the fragmentation/shear flow model of galaxy formation and are used as input to the viscous action presumed to begin as soon as a galactic disk forms. A simple differential equation is found to describe the turbulent viscous evolution of a flat disk. Solutions to this equation produce rotation curves that closely resemble those observed in spiral and elliptical galaxies. For spirals, by using the mass distributions derived from the rotation curves and from Seiden's theory of star formation, exponential luminosity profiles are produced.Los Alamos National Laboratory is operated by the University of California for the United States Department of Energy under contract W-7405-ENG-36. 相似文献
6.
Rotation curves of spiral galaxies in clusters are compared with their counterparts in the field using three criteria: (1) inner and outer velocity gradients, (2)M/L gradients, and (3) Burstein's mass type methodology. Both H emission-line rotation curves and more extendedHi rotation curves are used. A good correlation is found between the outer gradient of the rotation curve and the galaxy's distance from the centre of the cluster, in the sense that the inner galaxies tend to have falling rotation curves while the outer galaxies, and field galaxies, tend to have flat or rising rotation curves. A correlation is also found between theM/L gradient across a galaxy and the galaxy's position in the cluster, with the outer galaxies having steeperM/L gradients. Mass types for field spirals are shown to be a function of both Hubble-type and luminosity, contrary to earlier results. The statistical difference between the distribution of mass types in clusters and in the field reported by Bursteinet al. is confirmed. These correlations indicate that the inner cluster environment can strip away some fraction of the mass in the outer halo of a spiral galaxy, or alternatively, may not allow the halo to form. 相似文献
7.
G. A. Shchelkanova S. I. Blinnikov A. S. Saburova A. D. Dolgov 《Astronomy Letters》2013,39(10):665-675
The observed rotation curves of four low-surface-brightness galaxies are compared with the predictions of three models of the dark matter distribution with various degrees of singularity at the center or without it. Contrary to the assertions in the literature, the results of fitting the rotation curves by the least-squares method using a chi-square distribution with optimal parameters (dark matter halo, bulge, and disk) do not yet allow any one of the models to be uniquely preferred. The NFW and Burkert models have the highest significance levels for two of the four galaxies and for the other two, respectively. At the same time, using the NFW model in the latter two cases leads to an estimate of the disk surface density close to the photometric one, which may suggest that these models are more realistic. The surface density estimates for the galactic disks based the criterion of their marginal gravitational stability have also been used. The disks of the galaxies under consideration may be overheated, because the modeling using these estimates gives larger deviations of the model rotation curves from the observed ones than in the case where the surface density is assumed to be a free parameter. Using the disk surface density estimates based on the criterion of marginal gravitational stability does not change the preference in choosing the shape of the dark matter density profile in the galaxies under consideration compared to the case with a “free disk.” 相似文献
8.
R. H. Sanders 《Astronomy and Astrophysics Review》1990,2(1):1-28
Neutral hydrogen line observations of the extended rotation curves of spiral galaxies imply that there exist significant discrepancies between the luminous and dynamical mass beyond the bright optical discs. This means either that galaxies contain significant quantities of non-luminous matter (matter with a mass-to-light ratio very much higher than that of ordinary stars), or that the law of gravity on the scale of galaxies is not the usual Newtonian inverse square law. Attempts to account for the observed discrepancy in the context of these two explanations are reviewed here with emphasis given to the second and less conventional alternative. It is argued that the standard picture of spiral galaxy halo and disc formation in the context of cold dark matter cannot account for the observed systematics of the discrepancy — notably rotation curves which are seen to be flat and featureless from the bright inner regions where the visible matter dominates the dynamics (in some cases overwhelmingly) to the outer regions where the dark halo dominates. It is demonstrated that in those galaxies with well-observed rotation curves, the discrepancy apparently appears below a critical acceleration. Any dark matter explanation of the discrepancy must account for this fact. Moreover, this would also eliminate empirically motivated modifications of Newton's law in which the deviation from 1/r occurs beyond a fundamental length scale. The suggestion by Milgrom in which the force law becomes essentially 1/r below a critical acceleration (MOND) can account for most of the observed systematics of galaxy rotation curves and, significantly, leads to the observed luminosity-velocity relationship in spiral galaxies (the Tully-Fisher law). Generally covariant theories of gravity which predict this phenomenology in the weak-field limit are described. Although there is not yet a theory which obviously meets all of the requirements for a physically viable alternative to dark matter, a generalized scalar-tensor theory of the form suggested by Bekenstein (phase coupling gravitation) is the currently leading candidate and has the advantage of being testable locally. 相似文献
9.
An overview of the currently available methods for finding the unstable modes of a stellar disk within the framework of linear perturbation theory is given. The galaxy models with gradually rising and flat rotation curves are used as examples to show the existence of various kinds of spectra of unstable modes. The peculiarities of the spectra are discussed. The spectrum of the model with a (flat) rotation curve rapidly rising at the center is provided for the first time. The method that relies on a biorthogonal basis expansion of the perturbed potential and surface density is shown to have limited applicability due to the shortage of appropriate basis functions. The finite element method successfully applied in other areas of science and engineering is sensitive in its current implementation to the presence of regions with resonant orbits. 相似文献
10.
A. V. Zasov A. V. Khoperskov I. Yu. Katkov V. L. Afanasiev S. S. Kaisin 《Astrophysical Bulletin》2012,67(4):362-373
We present the results of spectroscopic observations of three S0-Sa galaxies: NGC 338, NGC 3245, and NGC 5440 at the SAO RAS 6-m BTA telescope. The radial distributions of the line-ofsight velocities and radial velocity dispersions of stars and ionized gas were obtained, and rotation curves of galaxies were computed. We construct the numerical dynamic N-body galaxy models with N ?? 106 points. The models include three components: a ??live?? bulge, a collisionless disk, dynamically evolving to the marginally stable state, and a pseudo-isothermal dark halo. The estimates of radial velocities and velocity dispersions of stars obtained from observations are compared with model estimates, projected onto the line of sight. We show that the disks of NGC 5440 and the outer regions of NGC 338 are dynamically overheated. Taking into account the previously obtained observations, we conclude that the dynamic heating of the disk is present in a large number of early-type disk galaxies, and it seems to ensue from the external effects. The estimates of the disk mass and relative mass of the dark halo are given, as well as the disk mass-to-luminosity ratio for seven galaxies, observed at the BTA. 相似文献
11.
A. V. Moiseev 《Astrophysical Bulletin》2014,69(1):1-20
We present the results of study of the ionized gas velocity fields in 28 nearby (systemic velocity below 1000 km s?1) dwarf galaxies. The observations were made at the 6-m BTA telescope of the SAO RAS with the scanning Fabry-Perot interferometer in the Hα emission line. We were able to measure regular circular rotation parameters in 25 galaxies. As a rule, rotation velocities measured in HII are in a good agreement with the data on the HI kinematics at the same radii. Three galaxies reveal position angles of the kinematic axis in the HII velocity fields that strongly (tens of degrees) differ from the measurements in neutral hydrogen at large distances from the center or from the orientation of the major axis of optical isophotes. The planes of the gaseous and stellar disks in these galaxies most likely do not coincide. Namely, in DDO99 the gaseous disk is warped beyond the optical radius, and in UGC3672 and UGC8508 the inclination of orbits of gas clouds varies in the inner regions of galaxies. It is possible that the entire ionized gas in UGC8508 rotates in the plane polar to the stellar disk. 相似文献
12.
Extensive and meticulous observations of the rotation curves of galaxies show that they are either flat or gently going up,
but rarely decreasing, at large galactocentric distances. Here we show that the gravitational potential which would lead to
such rotation curves arises naturally when the visible matter modelled as a collisionless Maxwellian gas is embedded in a
dark halo of collisionless particles with a much higher dispersion in velocities. 相似文献
13.
It is shown that a gas of massive bosonic particles (m
60 eV), e.g. Higgs particles, surrounding disk galaxies is able to generate the flat rotation curves of spiral galaxies without internal difficulties with physical principles. We have analyzed 36 galaxies and find good agreement with the empirical data. 相似文献
14.
Eva Gessner 《Astrophysics and Space Science》1992,196(1):29-43
In this paper we reproduce flat rotation curves of spiral galaxies by discussing a scalar tensor theory of gravity which includes the Higgs field as scalar field. The galaxy density distribution is assumed to be homogeneous or polytropic and in the galaxy core there exists a large concentrated mass. 相似文献
15.
F. Rahaman M. Kalam A. DeBenedictis A. A. Usmani Saibal Ray 《Monthly notices of the Royal Astronomical Society》2008,389(1):27-33
In the present investigation, flat rotational curves of the galaxies are considered under the framework of brane-world models where the four-dimensional effective Einstein equation has extra terms which arise from the embedding of the 3-brane in the five-dimensional bulk. It has been shown here that these long-range bulk gravitational degrees of freedom can act as a mechanism to yield the observed galactic rotation curves without the need for dark matter. The present model has the advantage that the observed rotation curves result solely from well-established non-local effects of gravitation, such as dark radiation and dark pressure under a direct use of the condition of flat rotation curves and does not invoke any exotic matter field. 相似文献
16.
We consider the effects of projection, absorption, and velocity dispersion on the shape of the rotation curve for a galaxy as a function of its disk inclination to the plane of the sky. We conclude that for galaxies with a fairly massive compact bulge these effects lead to a marked discrepancy between the rotation curve and the circular velocity curve even if their disks are viewed far from edge-on, especially for the rotation curves constructed from observations of the stellar component. 相似文献
17.
I.A. Yegorova A. Babic P. Salucci K. Spekkens A. Pizzella 《Astronomische Nachrichten》2011,332(8):846-853
We have investigated the stellar light distribution and the rotation curves of high‐luminosity spiral galaxies in the local Universe. The sample contains 30 high‐quality extended Hα and H I rotation curves. The stellar disk scale‐length of these objects was measured or taken from the literature. We find that in the outermost parts of the stellar disks of these massive objects, the rotation curves agree with the Universal Rotation Curve (Salucci et al. 2007), however a few rotation curves of the sample show a divergence (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
It is shown that a gas of massive bosonic particles (
eV), e.g. Higgs particles, surrounding the disk galaxies is able to generate flat rotation curves without internal difficulties with physical principles. 相似文献
19.
A method to fit flat rotation curves is presented, wherein the galactic density for a disk model is expressed in terms of a Dirichlet polynomial. This procedure allows us to obtain the total galactic mass and to predict the circular velocity at large galactocentric distances.Application of the method to the Galaxy, M31 and four Sc galaxies shows that a significant galactic mass is located beyond the optical radius although it is considerably smaller than the integral mass values obtained from current models with a massive corona included. Observed rotation curves and convergent total mass are obtained, thus the total mass for the Milky Way Galaxy is 5.69×1011
M
. 相似文献
20.
T.G. Arshakian R. Stepanov R. Beck M. Krause D. Sokoloff 《Astronomische Nachrichten》2011,332(5):524-536
Future radio observations with the Square Kilometre Array (SKA) and its precursors will be sensitive to trace spiral galaxies and their magnetic field configurations up to redshift z ≈ 3. We suggest an evolutionary model for the magnetic configuration in star‐forming disk galaxies and simulate the magnetic field distribution, the total and polarized synchrotron emission, and the Faraday rotation measures for disk galaxies at z ≲ 3. Since details of dynamo action in young galaxies are quite uncertain, we model the dynamo action heuristically relying only on well‐established ideas of the form and evolution of magnetic fields produced by the mean‐field dynamo in a thin disk. We assume a small‐scale seed field which is then amplified by the small‐scale turbulent dynamo up to energy equipartition with kinetic energy of turbulence. The large‐scale galactic dynamo starts from seed fields of 100 pc and an averaged regular field strength of 0.02 μG, which then evolves to a “spotty” magnetic field configuration in about 0.8 Gyr with scales of about one kpc and an averaged regular field strength of 0.6 μG. The evolution of these magnetic spots is simulated under the influence of star formation, dynamo action, stretching by differential rotation of the disk, and turbulent diffusion. The evolution of the regular magnetic field in a disk of a spiral galaxy, as well as the expected total intensity, linear polarization and Faraday rotation are simulated in the rest frame of a galaxy at 5GHz and 150 MHz and in the rest frame of the observer at 150 MHz. We present the corresponding maps for several epochs after disk formation. Dynamo theory predicts the generation of large‐scale coherent field patterns (“modes”). The timescale of this process is comparable to that of the galaxy age. Many galaxies are expected not to host fully coherent fields at the present epoch, especially those which suffered from major mergers or interactions with other galaxies. A comparison of our predictions with existing observations of spiral galaxies is given and discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献