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1.
对于星系际弥散恒星的研究是分别从观测、数值模拟和半解析模型这三个方面进行的.现在已经在邻近星系团及中低红移处观测到弥散恒星,甚至在Virgo及Coma星系团中观测到了单个的弥散恒星.观测数据的积累使得人们能够从统计上了解星系际弥散恒星的性质.研究表明星系际弥散恒星围绕着星系团势阱中心呈椭球状对称分布,其在星系团恒星总质... 相似文献
2.
星系中心黑洞质量和核球恒星速度弥散度的紧密关系揭示出准确测量恒星速度弥散度对测定星系中心黑洞质量尤为重要.文中提供了一种利用SDSS(Sloan Digital SkySurvey)光谱测定速度弥散度及其不确定性的方法.通过对像素空间包含显著特征吸收线的4个不同谱区的拟合,得到准确测量恒星速度弥散度σ的光谱区域.文中4个拟合波段主要包含的吸收线为CaⅡK,MgⅠb三重线(波长5167.5,5172.7,5183.6(?))和CaT(CaⅡ三重线,波长8498.0,8542.1,8662.1(?)).不同区域结果表明,MgⅠb区由于受到铁族发射线影响,拟合的σ值偏低;CaⅡK线区谱线强度很弱,易受限于最小二乘法搜索算法;CaT+CaⅡK联合区得出的速度弥散度和只计算CaT区域的结果相当.利用该方法,测试了一个红移小于0.05的赛弗特星系样本,发现CaT区是测速度弥散度的最佳谱区. 相似文献
3.
本文通过数值计算解出稳态星系模型，并与椭圆星系及旋涡星系核球的自转和弥散速度曲线相比较。由星系运动曲线传合出的星系半径与从光度曲线拟合出的潮汐半径不一致，后者总是前者的３倍左右，这是由于分布函数的截断方式不妥造成的。我们的结论是：该模型虽不能正确描述整个星系，但却能正确描述星系的较内部区域。我们分析了三个速度曲线资料的星系黑洞候选者：Ｍ１０４、Ｍ３１和银河系，发现它们由于有太快的自转，都不可能在达 相似文献
4.
5.
本文利用Virgo星系团天区572个星系的视向速度观测资料,按最大似然原理确定了434个成员星系。平均日心速度1247±37公里每秒,视向速度弥散度752±27公里·每秒。分析表明,尽管室女团是一个有次团结构的近距星系团,仍然可以合理地用正态分布来作为成员星系观测视向速度分布的一级近似。另外,团内不同类型的星系看来有着不同的分布,而晚型星系可能仍然处于内落阶段。 相似文献
6.
Chandrasekhar等和Sunder等讨论了具有局部各向同性速度分布的旋转椭球星系的短期（远小于哈勃时间）演化,本文运用Laskar的频率分析方法研究这种星系的长期（大于哈勃时间）演化．得到的新结论主要有：（1）这种星系存在唯一的平衡态（球对称平衡态）,它是临界线性稳定的;（2）其半轴一般在平衡态的半径邻近作拟周期或近拟周期（这种近似在远大于哈勃时间后仍可行）振动,从而是长期稳定的;（3）存在一个半轴趋于零,另一个半轴趋于有限值的情形,且一般趋于零的是对称轴的轴长（从而星系趋于扁平）,这意味着某些盘星系可能来源于具旋转棉球构形的星系前物质． 相似文献
7.
本文通过数值计算解出稳态星系模型，并与椭圆星系及旋涡星系核球的自转和弥散速度曲线相比较。由星系运动曲线拟合出的星系半径与从光度曲线拟合出的潮汐半径不一致，后者总是前者的３倍左右，这是由于分布函数的截断方式不妥造成的。我们的结论是：该模型虽不能正确描述整个星系，但却能正确描述星系的较内部区域，我们分析了三个有速度曲线资料的星系黑洞候选者：Ｍ１０４、Ｍ３１和银河系，发现它们由于有太快的自转，都不可能在达到稳态之后有满足形成黑洞所要求的≡ｃＪ／ＧＭ２＜１的区域存在，因此它们的中心如有黑洞，只能有更早的起源。 相似文献
8.
总结了到目前为止用所谓Lyman Break方法（亦称为UV drop方法）观测得到的高红移（z≈3）Lyman break星系的观测特征，包括光度函数、半光度半径分布、空间密度及成团性、恒星速度弥散、超星风及大尺度气体团块运动和金属丰度等。还对目前的理论工作做了综合介绍，对当前两种主要模型进行了评述并提出了作者的个人观点。 相似文献
9.
熊永清 《中国科学院上海天文台年刊》1999,(20):91-97
与Geiger和Santerre的简单的均匀分布假设进行比较,本较严格地考虑了GPS卫星天空分布密度随赤纬和轨道倾角的变化,研制了SIMSKY软件,采用模拟计算的方法研究了GPS星座对精密定位误差椭球大小和三轴指向的作用;还研究钟差与测站坐标的相关程度。这种方法可以用于研究不同纬度的测站网络对误差椭球和z-t相关性的影响、不同截止高度对误差椭球和高程与时间相关性的影响。 相似文献
10.
黄松年 《中国科学院上海天文台年刊》1989,(10):134-136
本用了一个均匀密度的三轴椭球晕，对沉浸在其中的非轴对称盘星系受到的扭矩作了一级近似计算。这个扭矩虽然量级很小，但对盘星系的角动量演化是一个长期的效应。 相似文献
11.
选取前文中所列出的29个累积光谱型为F型的球状星团中的3个作为样本，深入研究了初始观测资料的不确定性和选用不同的银河系引力势模型，对样本星团轨道参数的影响。首先采用Monte Carlo方法产生3个样本球状星团的模拟初始观测数据，而后，以这些模拟数据为初始条件，在3种不同的银河系引力势模型下进行轨道计算，得到此3个样本的模拟轨道参数。模拟计算的结果表明：根据模拟初始数据生成的样本轨道参数分布形态大致可分为高斯分布、准高斯分布和非高斯分布等3类；初始观测数据的不确定性对样本轨道参数分布的影响，与样本星团的选择和轨道参数的类型有关；选用不同的银河系引力势模型，对3个样本星团的各个轨道参数的分布和形态结构也会产生不同程度的影响。该工作的结果，可供深入研究球状星团的整体运动和动力学性质等问题参考。 相似文献
12.
Naoki Yoshida † Ravi K. Sheth Antonaldo Diaferio 《Monthly notices of the Royal Astronomical Society》2001,328(2):669-677
We use numerical simulations of a (480 Mpc h −1 )3 volume to show that the distribution of peak heights in maps of the temperature fluctuations from the kinematic and thermal Sunyaev–Zeldovich (SZ) effects will be highly non-Gaussian, and very different from the peak-height distribution of a Gaussian random field. We then show that it is a good approximation to assume that each peak in either SZ effect is associated with one and only one dark matter halo. This allows us to use our knowledge of the properties of haloes to estimate the peak-height distributions. At fixed optical depth, the distribution of peak heights resulting from the kinematic effect is Gaussian, with a width that is approximately proportional to the optical depth; the non-Gaussianity comes from summing over a range of optical depths. The optical depth is an increasing function of halo mass and the distribution of halo speeds is Gaussian, with a dispersion that is approximately independent of halo mass. This means that observations of the kinematic effect can be used to put constraints on how the abundance of massive clusters evolves, and on the evolution of cluster velocities. The non-Gaussianity of the thermal effect, on the other hand, comes primarily from the fact that, on average, the effect is larger in more massive haloes, and the distribution of halo masses is highly non-Gaussian. We also show that because haloes of the same mass may have a range of density and velocity dispersion profiles, the relation between halo mass and the amplitude of the thermal effect is not deterministic, but has some scatter. 相似文献
13.
Groups of galaxies are identified on the basis of the CfA2 redshift survey and a method proposed by one of the authors. Of
the 15577 galaxies that have redshifts of 1000-15000 km/s and lie at galactic latitudes |bII| ≥ 20° , 1971 groups with n ≥
2 members were found, with a combined total number of 6787 members. The remaining 8790 (56.4%) galaxies constitute a sample
of “single,” isolated galaxies. The dispersion in the radial velocities of the groups and their radii are found to depend
weakly on the distance to the observer. 相似文献
14.
A series of numerical experiments is carried out to simulate the dynamical evolution of groups of galaxies in different models
of gravitation. The simulation results are compared with observations of the Local Group and of the CenA/M83 and M81/M82 galactic
groups. It is found that the LCDM model and the MOND (Modified Newtonian Dynamics) model are in substantially better agreement
with the observations than the other two models examined here. The dispersion in the velocities relative to Hubble’s law in
these models is small, but the MOND model yields slightly elevated values. For initial conditions close to virial equilibrium,
the mean square deviations in the velocities of the galaxies are ~30 km/s, in agreement with observational estimates. 相似文献
15.
Rekhesh Mohan K. S. Dwarakanath G. Srinivasan 《Journal of Astrophysics and Astronomy》2004,25(3-4):185-201
We have carried out a sensitive high-latitude (|b| > 15°) HI 21 cm-line absorption survey towards 102 sources using the GMRT. With a 3σ detection limit in optical depth of
∼ 0.01, this is the most sensitive HI absorption survey. We detected 126 absorption features most of which also have corresponding
HI emission features in the Leiden Dwingeloo Survey of Galactic neutral Hydrogen. The histogram of random velocities of the
absorption features is well-fit by two Gaussians centered at V1sr ∼ 0 km s−1 with velocity dispersions of 7.6 ± 0.3 km s−1 and 21 ± 4 km s−1 respectively. About 20% of the HI absorption features form the larger velocity dispersion component. The HI absorption features
forming the narrow Gaussian have a mean optical depth of 0.20 ± 0.19, a mean HI column density of (1.46 ± 1.03) × 1020 cm−2, and a mean spin temperature of 121 ± 69 K. These HI concentrations can be identified with the standard HI clouds in the
cold neutral medium of the Galaxy. The HI absorption features forming the wider Gaussian have a mean optical depth of 0.04
± 0.02, a mean HI column density of (4.3 ± 3.4) × 1019 cm−2, and a mean spin temperature of 125 ± 82 K. The HI column densities of these fast clouds decrease with their increasing random
velocities. These fast clouds can be identified with a population of clouds detected so far only in optical absorption and
in HI emission lines with a similar velocity dispersion. This population of fast clouds is likely to be in the lower Galactic
Halo. 相似文献
16.
C. Halliday † Roger L. Davies Harald Kuntschner M. Birkinshaw Ralf Bender R.P. Saglia Glenn Baggley 《Monthly notices of the Royal Astronomical Society》2001,326(2):473-489
The shape of the line-of-sight velocity distribution (LOSVD) is measured for a sample of 14 elliptical galaxies, predominantly low-luminosity ellipticals. The sample is dominated by galaxies in the Virgo cluster but also contains ellipticals in nearby groups and low-density environments. The parametrization of the LOSVD given by Gerhard and van der Marel & Franx is adopted, which measures the asymmetrical and symmetrical deviations of the LOSVD from a Gaussian by the amplitudes h 3 and h 4 of the Gauss–Hermite series. Rotation, velocity dispersion, h 3 and h 4 are determined as a function of radius for both major and minor axes. Non-Gaussian LOSVDs are found for all galaxies along the major axes. Deviations from a Gaussian LOSVD along the minor axis are of much lower amplitude if present at all. Central decreases in velocity dispersion are found for three galaxies. Two galaxies have kinematically decoupled cores: NGC 4458 and the well-known case of NGC 3608. 相似文献
17.
The values of the initial velocity of the meteoroids ejected from the parent bodies are small and as a result, the most of the young meteoroid streams have similar orbits to their parent bodies. Assuming that the members of the observed meteor stream evolved under the influence of gravitational perturbations mostly, Pittich [1991, Proceedings of the Conference on Dynamic of Small Bodies of the Solar System, Polish-Slovak Conference, Warsaw, October 25–28, 1988, pp. 55-61], Williams [1996, Earth, Moon, Planets
72, 321–326; 2001, Proceedings of the Meteoroids 2001 conference, Kiruna, Sweden, August 6–10, 2001, pp. 33–42] estimated the ejection velocities of the stream meteoroids. Equation relating the ejection velocity Δυ and the change Δa of the semi-major axis, Williams (2001), was applied with two slightly different variations. In the first one (M1) as Δa the difference between the mean orbit of the stream and the orbit of the parent body was substituted, in the second one (M2), as Δa the dispersion of semi-major axes around the mean orbit of the stream was used. The results obtained by these two methods are not free from discrepancies, partly explained by the particular orbital structure of the stream. Kresak [1992, Contrib. Astron. Obs. Skalnate Pleso
22, 123–130] strongly criticized the attempts to determine the initial velocities of the stream using the statistics of the meteor orbits. He argued that this is essentially impossible, because the dispersion of the initial velocities are masked by much larger measuring errors and by the accumulated effects of planetary perturbations. In our paper, we study the reliability of M1 and M2 methods. We made a numerical experiment consisting of formation of several meteor streams and their dynamical evolution over 5000 years. We ejected meteoroids particles from the comets: 1P/Halley, 2P/Encke, 55P/Tempel-Tuttle, 109P/Swift-Tuttle and from minor planets (3200) Phaethon and 2002 SY50. During the integration, the ejection velocities were estimated using both M1 and M2 methods. The results show that the velocities obtained by M1 method are unstable: too high or too low, when compared with the known ejection velocities at the time of the stream formation. On the other hand, the velocities obtained using M2 method are too small, mostly. In principle, M2 estimates the dispersion of the distribution of the ejection velocities around the mean value, not the mean value itself. Applying more accurate Equation relating Δυ and Δa we decreased the bias of the results, but not their variation observed during the evolution of the streams and the parent bodies. We have found that the variability of the estimated ejection velocities was caused mainly by the gravitational changes of the semi-major axis and eccentricity of the parent body. In brief, we have found that the reliability of the results obtained by M1 or M2 method are low, and have to be used with great care. 相似文献
18.
J.Kleyna M. I.Wilkinson N. W.Evans G.Gilmore C.Frayn 《Monthly notices of the Royal Astronomical Society》2002,330(4):792-806
We present stellar radial velocity data for the Draco dwarf spheroidal (dSph) galaxy obtained using the AF2/WYFFOS instrument combination on the William Herschel Telescope. Our data set consists of 186 member stars, 159 of which have good quality velocities, extending to a magnitude V ≈19.5 with a mean velocity precision of ≈2 km s−1 . As this survey is based on a high-precision photometric target list, it contains many more Draco members at large radii. For the first time, this allows a robust determination of the radial behaviour of the velocity dispersion in a dSph.
We find statistically strong evidence of a rising velocity dispersion consistent with a dark matter halo that has a gently rising rotation curve. There is a <2 σ signature of rotation about the long axis, inconsistent with tidal disruption as the source of the rising dispersion. By comparing our data set with earlier velocities, we find that Draco probably has a binary distribution and fraction comparable to those in the solar neighbourhood.
We apply a novel maximum likelihood algorithm and fit the velocity data to a two parameter spherical model with an adjustable dark matter content and velocity anisotropy. Draco is best fit by a weakly tangentially anisotropic distribution of stellar orbits in a dark matter halo with a very slowly rising rotation law ( vcirc ∝ r 0.17 ) . We are able to rule out both a mass-follows-light distribution and an extended halo with a harmonic core at the 2.5 to 3 σ significance level, depending on the details of our assumptions about Draco's stellar binary population. Our modelling lends support to the idea that the dark matter in dwarf spheroidals is distributed in the form of massive, nearly isothermal haloes. 相似文献
We find statistically strong evidence of a rising velocity dispersion consistent with a dark matter halo that has a gently rising rotation curve. There is a <2 σ signature of rotation about the long axis, inconsistent with tidal disruption as the source of the rising dispersion. By comparing our data set with earlier velocities, we find that Draco probably has a binary distribution and fraction comparable to those in the solar neighbourhood.
We apply a novel maximum likelihood algorithm and fit the velocity data to a two parameter spherical model with an adjustable dark matter content and velocity anisotropy. Draco is best fit by a weakly tangentially anisotropic distribution of stellar orbits in a dark matter halo with a very slowly rising rotation law ( v
19.
William B. Heard 《Astrophysics and Space Science》1976,43(1):63-82
The dynamics of an ensemble of particles emanating from a common point with a distribution of velocities is modeled as a continuum of particles described by a phase space distribution function. A general solution for the distribution function and the associated spatial density function is obtained for a general dynamical system. The special cases of linear dynamical systems and slow dispersion from a circular orbit are treated in detail. A transcendental equation is derived, the roots of which determine the time since initial dispersion from knowledge of the spatial density function at later times. 相似文献
20.
The study of nonequilibrium, self-gravitating, compressible, homogeneous and uniformly rotating gaseous ellipsoidal models
is extended from parallel to nonparallel angular velocity and vorticity. The differential equations of motion governing these
models are numerically integrated over ranges of initial values of angular velocity and vorticity.
The dynamical behaviour of the ellipsoid is found to be almost unchanged when the initial values of Ω3/Ω3,e and λ3/λ3,e are interchanged, where λ is a function of the vorticity, Ω3 is the angular velocity along the x3 axis, and Ω3,e and λ3,e are equilibrium values.
Models with the same initial value of | Ω3/Ω3,e - λ3/λ3,e | have similar dynamical behaviour. When this value becomes larger, the oscillations of the semi-axes are larger and are
more nonperiodic.
For all models, the ellipsoidal configuration is maintained at all times.
The magnitude of Ωl depends on the difference between the values of the semi-axes am and an, where l, m, and n are cyclic. The smaller this difference is, the larger the angular velocity along the third axis. Thus
whenever the model approaches a spheroidal configuration, there may be a large and rapid increase in the angular velocity
along the axis of ‘symmetry’.
The last two properties, namely the maintenance of the ellipsoidal configuration and the large increase in angular velocity
of the model, configuration also hold in the model (T.T.Chia and S.Y.Pung, 1995, Astrophys.\ Space Sci., 229, 215.) with parallel
angular velocity and vorticity.
However, unlike the earlier model, Ω2 and Ω3 are observed to reverse their directions at certain instants during the oscillations; this may have interesting astrophysical
implications.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献