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1.
R. H. Miller 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):307-324
Numerical experiments undertaken to investigate the longevity and behavior of dark-lane elliptical galaxies are described. This is dynamically the same problem as a disk galaxy in a massive halo. Spiral galaxies are disks from a dynamical point of view. A disk of particles embedded in a self-consistent galaxy provides the basic model used for the experiments. This model is applicable to ordinary disk galaxies if the disk is interpreted as the visible galaxy and the galaxy is interpreted as the massive halo thought to be present around disk galaxies. Fully three-dimensional fully self-consistentn-body computer programs that can handle 100,000 particles are used for the experiments. The background galaxy is oblate, and the disk is inclined to the axis of the oblate galaxy, so the disk precesses differentially to produce a warp. A surprising result is that the galaxy center shifted, leaving the disk center orbiting around the galaxy center. This produces interesting phenomena reminiscent of observations in the region of the Galactic center. 相似文献
2.
P. M. S. Namboodiri K. S. Sastry K. S. V. V. S. Narasimhan 《Astrophysics and Space Science》2006,301(1-4):3-9
Numerical simulations are performed to study the tidal effects of non-merging rapid head-on collision between a disk galaxy
and a spherical galaxy. The disk consists of three components – a disk, a bulge and a halo – and the spherical galaxy is a
Plummer model. The galaxies have the same dimensions with different mass ratios viz., 2, 1 and 0.5. They move in a rectilinear
orbit with a relative velocity of 1000 km s−1.
None of the simulations leads to the merger of the galaxies by tidal capture. The results of our simulations indicate that
although tidal effects are sensitive to both the mass ratio and the inclination of the disk to the orbital plane, it is the
mass ratio which is more important in producing tidal damage to the less massive galaxy. The spherical galaxy undergoes considerable
tidal effects if the mass of the disk is same or larger. On the other hand the collisions in which the mass of the spherical
galaxy is more, result in the formation of a ring structure after the closest approach and the structure disappears by the
end of the simulations. 相似文献
3.
M. Faúndez-Abans V. P. Reshetnikov M. de Oliveira-Abans I. F. Fernandes 《Astronomy Letters》2009,35(1):25-32
We present the results of our spectroscopic and morphological studies of the galaxy UGC 7388 with the 8.1-m Gemini North telescope. Judging by its observed characteristics, UGC 7388 is a giant late-type spiral galaxy seen nearly edge-on. The main body of the galaxy is surrounded by two faint (μ B ～ 24 m /□″ and μ B ～ 25 · m 5/□″) extended (～ 20–30 kpc) loop-like structures. A large-scale rotation of the brighter loop about the main galaxy has been detected. We discuss the assumption that the tidal disruption of a relatively massive companion is observed in the case of UGC 7388. A detailed study and modeling of the observed structure of this unique galaxy can give important information about the influence of the absorption of massive companions on the galactic disks and about the structure of the dark halo around UGC 7388. 相似文献
4.
Markus Samland 《Astrophysics and Space Science》2002,281(1-2):305-308
The formation of a disk galaxy within a slowly growing dark halo is simulated with a new chemo-dynamical model. The model
describes the evolution of the stellar populations, the multi-phase ISM and all important interaction. I find, that the galaxy
forms radially from inside-out and vertically from top-to-bottom. The derived stellar age distributions show that the inner
halo is the oldest component, followed by the outer halo, the triaxial bulge, the halo-disk transition region and the disk.
Despite the still idealized model, the final galaxy resembles present-day disk galaxies in many aspects. In particular, the
stellar metallicity distribution in the halo of the model resembles the one of M31. The bulge in the model shows, at least
two stellar subpopulations, an early collapse population and a population that formed later out of accreted disk mass. In
the stellar metallicity distribution of the disk, I find a pronounced ‘G-dwarf problem’ which is the result of a pre-enrichment
of the disk ISM with metal-rich gas from the bulge.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
5.
Gene G. Byrd M. Thomasson K. J. Donner B. Sundelius T. Y. Huang M. J. Valtonen 《Celestial Mechanics and Dynamical Astronomy》1988,45(1-3):31-36
We study, theoretically and with N-body simulations, the formation of spiral patterns in retrograde galaxy encounters. A one-armed leading spiral dominates in a disk if the tidal perturbation from the companion is large and the disk is surrounded by a massive halo. Otherwise, a trailing pattern forms. The leading arm is made up of particles in slightly elongated orbits whose turning points outline the arm. The arm rotates opposite to the disk rotation. We have found one spiral galaxy, NGC4622, with a leading arm near its nucleus. From the literature, we find that very few spirals, if any, in a sample of strongly perturbed galaxies have leading arms. A possible reason for this is that few spiral galaxies have a halo with larger mass than the disk within the visible disk. 相似文献
6.
Multicolor BVRI surface photometry of the low-luminosity (M V ≈?18m) spiral galaxy NGC 4136 is presented. The photometric parameters of its components and the color distribution over the galactic disk are estimated. The color indices and the corresponding effective ages are determined for the brightest star-forming regions. The disk-to-dark halo mass ratio is derived from the measured rotation curve of the galaxy. The disk mass dominates within the optical boundaries of the galaxy, so its disk can be considered as a self-gravitating system. 相似文献
7.
Alfonso Aragón-Salamanca Bo Milvang-Jensen George Hau Inger Jørgensen Jens Hjorth 《Astrophysics and Space Science》2002,281(1-2):339-342
We are carrying out a programme to measure the evolution of the stellar and dynamical masses and M/L ratios for a sizeable sample of morphologically-classified disk galaxies in rich galaxy clusters at 0.2 < z < 0.9. Using FORS2 at the VLT we are obtaining rotation curves for the cluster spirals so that their Tully-Fisher relation
can be studied as a function of redshift and compared with that of field spirals. We already have rotation curves for ∼ 10
cluster spirals at z = 0.83, and 25 field spirals at lower redshifts and we plan to increase this sample by one order of magnitude. We present
here the first results of our study, and discuss the implications of our data in the context of current ideas and models of
galaxy formation and evolution.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
8.
Tapan K. Chatterjee 《Astrophysics and Space Science》1981,76(2):491-502
The tidal force effects of a spherical galaxy passing head-on through a disk galaxy have been studied at various regions of the disk galaxy and for various orientations of the disk galaxy with respect to the direction of relative motion of the two galaxies. The density distribution of the disk galaxy is taken to be, (r)=ce–4r/R
, where c is the central density andR is the radius of the disk. The density distribution of the spherical galaxy is taken to be that of a oolytrope of indexn=4. It is found that as a result of the collision, through the central parts and the outer parts of the disk galaxy remain intact, the region in between these two regions disrupts. Thus a ring galaxy with a nucleus embedded in the ring-i.e., a ring galaxy of the RN-type, is formed. 相似文献
9.
Dynamical friction is incorporated in the numerical modeling of colliding ring galaxies. We show that dynamical friction may lead to the capture of an initially unbound companion into a damped oscillatory orbit before ultimately merging with the target disk. In the late stages of its motion the companion may be virtually merged with the main galaxy while rings are still propagating in the disk. This raises the possibility that there exist (at least) two classes of ring galaxies: a class of ring galaxies with separate detached companions in which dynamical friction is too weak to have captured the collider, and a second class with no apparent companion in which the latter has either merged with the target galaxy or has disrupted. These two classes could possibly be identified with O-type and P-type ring galaxies of Few and Madore (1986). 相似文献
10.
河外旋涡星系外区普遍存在翘曲结构,其特征可用干翘曲参数来描述,包括翘曲角、翘曲半径、不对称度等。一些翘曲星系表已相继发表,并用于相关的统计分析。关于翘曲盘的形成已提出多种理论机制,如星系间的潮汐相互作用、星系际介质的吸积、盘与暗晕的角动量错向以及星系际磁场的作用等。 相似文献
11.
The time evolution of barred structures is examined under the influence of the external forces exerted by a spherical halo and by prolate halos. In particular, galaxy disks are placed in the plane including the major axis of prolate halos, whose configuration is often found in cosmological simulations. N-body disks in fixed external halo fields are simulated, so that bars are formed via dynamical instability. In the subsequent evolution, the bars in prolate halos dissolve gradually with time, while the bar pattern in a spherical halo remains almost unchanged to the end of the simulation. The decay times of the bars suggest that they can be destroyed in a time smaller than a Hubble time. Our results indicate that this dissolution process could occur in real barred galaxies, if they are surrounded by massive dark prolate halos, and the configuration adopted here is not unusual from the viewpoint of galaxy formation. For a prolate halo model, an additional simulation that is restricted to two-dimensional in-plane motions has also ended up with similar bar dissolution. This means that the vertical motions of disk stars do not play an essential role in the bar dissolution demonstrated here. 相似文献
12.
《New Astronomy》2007,12(1):11-19
We present a dynamical model for an active galaxy. Our model is a mass model with a disk, nucleus, and halo components. Numerical calculations and theoretical evidence show, that for a fixed value of mass of the galaxy the stellar velocities in the central region decrease as the mass of halo increases. Furthermore, the motion tends to be regular while, when the halo component is absent, the majority of orbits are chaotic. The dynamical evolution of the system is also studied when mass is transported from the halo to the disk and the nucleus. Our results are compared to the recently obtained observation data for active galaxies. 相似文献
13.
The tidal force effects of a spherical galaxy passing head-on through a disk galaxy have been studied for various orientations of the disk galaxy with respect to the direction of relative motion of the two galaxies. The density distribution of the spherical galaxy is taken to be that of a polytrope of indexn=4 and that of the disk galaxy is taken to be, (r)=ce–4r/R, where c is the central density andR the radius of the disk. It is found that the disruptive effects due to the tidal force are minimum when the plane of the disk lies along the direction of relative motion, but are maximum when the plane of the disk is slightly inclined to this direction (about 15°). The tidal force effects at the median radius have also been computed. The tadal force effects are much higher in the interior region of the disk. 相似文献
14.
We analyze the relationship between the mass of a spherical component and the minimum possible thickness of stable stellar disks. This relationship for real galaxies allows the lower limit on the dark halo mass to be estimated (the thinner the stable stellar disk is, the more massive the dark halo must be). In our analysis, we use both theoretical relations and numerical N-body simulations of the dynamical evolution of thin disks in the presence of spherical components with different density profiles and different masses. We conclude that the theoretical relationship between the thickness of disk galaxies and the mass of their spherical components is a lower envelope for the model data points. We recommend using this theoretical relationship to estimate the lower limit for the dark halo mass in galaxies. The estimate obtained turns out to be weak. Even for the thinnest galaxies, the dark halo mass within four exponential disk scale lengths must be more than one stellar disk mass. 相似文献
15.
Song-nian Huang 《Chinese Astronomy and Astrophysics》1989,13(4):442-453
We discuss the different dynamical effects of spirals with live and rigid haloes in collisions. Our N-body simulation has 52000 particles. The target is a self-consistent three-dimensional system consisting of a disk and a live halo, the intruder galaxy has a fixed Plummer potential and moves in a straight line through the centre of the target in the plane of the disk. For comparison, the same numerical experiment is made with a rigid halo, all other conditions remaining the same. Differences in the dynamical response and the resulting morphology between the two cases are discussed. It is suggested that the torque on non-axial symmetric spirals exerted by triaxial haloes and the long term effect of dynamical friction of the halo should be further investigated. 相似文献
16.
The purpose of our work is to strongly constrain the mass to light ratio in the disk of the flocculent isolated Sc type spiral
NGC 4414 using a combined high resolution interferometric CO(1-0) and HI rotation curve, and deep HST B-V-I images of the
galaxy. To identify the mass contributions of the visible – stellar and gaseous – components, we observed the rotation curve
with high resolution in the optical disk. The M/L ratios we derive are low, about 1.5 in I band and 0.5 in K' band. The B
and V band M/L ratios vary greatly due to absorption by dust, reaching 4 in the molecular ring and decreasing to about 1.6
–1.8 at larger radii. This unequivocally shows that models, like most maximum disk models, assuming constant M/L ratios in
an optical waveband, simply are not appropriate. We illustrate this by making mock maximum disk models with a constant V band
M/L ratio. The key is having the central light distribution unobscured such that it can be used to trace the mass. The K'
band M/L ratio is virtually constant over the disk, suggesting that the intrinsic (unobscured) stellar M/L ratio is roughly
constant. We use our knowledge of the visible mass distribution to test disk and halo dark matter models. Fitting an NFW (Navarro
et al., 1996) halo to the rotation curve suggests that NGC 4414 is in a low mass concentrated halo typical of small galaxies
and early halo formation times.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
Photographic UBV photometry of NGC 2976, a low-luminosity member of the central M81 group of galaxies, is presented. Young stars in the central disk determine the optical view and the classification of this Sc(pec) galaxy. It is surrounded by a halo of an old population which contains nearly all the mass and half the luminosity of the system. This halo has some properties typical of spheroidal dwarf galaxies: an exponential brightness profile, an ellipticity trend of the isophotes typical of low-mass systems, and mass and luminosity near the upper limit of typical dwarfs. In the central population I disk, star formation proceeds in dense associations scattered irregularly in a broad ringlike region of 1.2 kpc radius just inside the turnover of the rotation curve. This star formation episode may last since some 108 a; it is possibly triggered by gas infall from the interstellar cloud generated during encounters between other group members in the central M81 group. A direct triggering by recent encounters is excluded since NGC 2976 is undisturbed in its outer parts. 相似文献
18.
A dynamical model composed of a disk galaxy with an elliptic companion, moving in a circular orbit, is used in order to study
the stellar orbits in a binary galaxy. Using the Poincare surface of section we study the evolution of the stochastic regions
in the primary galaxy considering the mass of the companion or the value of the Jacobi’s integral as a parameter. Our numerical
calculations suggest that the regions of stochasticity increase, as the mass of the companion or the value of the Jacobi’s
integral increase. An interesting observation is that only direct orbits become stochastic. 相似文献
19.
Toshio Tsuchiya 《Astrophysics and Space Science》2003,284(2):515-518
Dynamical evolution of galactic disks driven by interaction with satellite galaxies, particularly the problem of the disk
warping and thickening is studied numerically. One of the main purpose of the study is to resolve the long standing problem
of the origin of the disk warping. A possible cause of the warp is interaction with a satellite galaxy. In the case of the
Milky Way, the LMC has been considered as the candidate. Some linear analysis have already given a positive result, but one
had to wait for a fully self-consistent simulation as a proof. I have accomplished the numerical simulations with a million
particles, by introducing a hybrid algorithm, SCF-TREE. Those simulations give us quantitative estimates for the Milky Way
system. We have found an example in which large warp amplitudes are developed. We also found that the warp amplitudes depend
on the halo distribution. Among our three models, the most massive and spherical halo is preferable for the observable warp
excitation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
Acounter-rotating gas disk has been detected in the SA0 galaxy IC 560 located at the periphery of a sparse group of six late-type galaxies. The pattern of gas excitation and mid-infrared colors are indicative of ongoing star formation within 1 kpc of the center. Outside the gas disk with star formation the large-scale stellar disk of the galaxy has an old age and a very low metallicity, [Z/H] ≈ ?1. The source of external gas accretion onto IC 560 is undetected; the only option is a single infall of a companion rich in high-metallicity gas. 相似文献