共查询到19条相似文献,搜索用时 683 毫秒
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本文综述了近年来世界上各大天文台站对正常星系的射电连续辐射和HI辐射的观测及研究。引述各型星系(E星系、旋涡星系、星系对)及星系核的射电观测的主要结果及其统计性质,对其中一些结果的物理机制进行初步探讨。 相似文献
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Helou将双星系中的自旋方向的统计研究方法用到星系形成过程中,发现旋涡星系的自旋是反相关的,由此联想到在由星系并合过程中自旋对轨道倾角的依赖性。将Aarseth的标准N体模拟程序加上动力摩擦,形成一个研究星系并合的N体模拟程序,用来研究小星系群中星系的自旋和轨道倾角的依赖性。结果表明,在小星系群中,的确存在着类似旋涡星系中的自旋和轨道倾角的反相关性。 相似文献
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使用了目前最大的棒旋星系样本之一,着重于研究旋涡星系中央的比恒星形成率(sSFR)和棒结构的关系。我们用1g sSFR=-11 a~(-1)作为星系宁静态和活跃态的分界,统计对比了棒旋星系和非棒旋星系中央的sSFR,发现相对于非棒旋星系,棒旋星系处于中央宁静态的比重更大,而在中央活跃态其恒星形成活动更剧烈。为消除星系样本恒星质量差异对星系中央sSFR统计结果的影响,获得控制样本,使棒旋星系和非棒旋星系具有相同的恒星质量分布。随后发现这两类星系在中央宁静态中的统计差异消失,而在中央活跃态棒旋星系的恒星形成活动依旧相对剧烈,尤其体现在长棒星系中。这说明棒结构对旋涡星系中央的恒星形成起到促进作用,且作用效果与棒的长短相关。 相似文献
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传统的哈勃星系形态分类法可以很好地对近邻的亮星系进行分类,但对低面亮度星系、矮椭球星系、矮旋涡星系以及高红移星系等都已无能为力。德沃古勒分类系统、叶凯士分类系统和范登伯分类系统是在哈勃分类法的基础上进行了发展和细化,利用光的中心聚集度或光度级等作为星系形态分类的参数。模型化分类系统试图定量地测量星系形态参数,但需要假定星系面亮度分布满足一定的形式,如r~(1/4)律、指数律等。最近几年,又有一些学者提出了非模型化分类系统,给出了若干个可以直接测量星系形态的结构参数,如:聚集度指数C、非对称指数A、簇聚指数S、基尼系数G及矩指数M_(20)。这些参数可以反映星系的形成历史、恒星形成、与其他星系的相互作用、已经发生或正在进行的并合活动等。它们不仅可以有效地给出近邻星系的分类特性,还能用于测量高红移星系的形态。该文介绍了不同的星系形态分类方法,比较了各类方法的优点和不足。在此基础上,最后介绍了基于非模型化分类系统的星系形态分类的研究进展。 相似文献
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盘星系的内禀扁度对计算星系的空间倾角非常重要.对从LEDA数据库中选取的14988个盘星系进行内禀扁度的统计分析.研究表明,盘星系的内禀扁度与星系的形态密切相关.整体上说,透镜星系和不规则星系的内禀扁度qo大于旋涡星系,早型旋涡星系的内禀扁度qo大于晚型旋涡星系,其中Scd星系的内禀扁度qo最小.利用所得的qo-T关系,还对16个已知倾角的亮星系进行了倾角计算,发现与其他方法估计的空间倾角符合得较好. 相似文献
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使用澳大利亚AT对6个近距中等红外光度的IRAS星系在双频上同时进行了观测.其中IRAS20272-4738、IRAS23156-4238探测到射电发射.获得了它们的射电流量、峰值位置、源的大小、频谱指数等射电参数,用红外、射电、光学资料对射电源进行了证认.并结合以前的观测资料讨论了这类星系射电发射的特点. 相似文献
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本文对IRAS暗源表中4个选区的IRAS星系的两点角相关函数,关联分维进行了计算,结果表明,所有选区内的星系呈现小角尺度上的成团,在较大角尺度上,分布可以用多级分形很好地表示,在更大角尺度上,用非归一星系对计数可以探测到密度分布中可能存在的典型惊讶,当取4个选区的平均值作为IRAS星系在宙宇中分布情况的代表时,所得结果与用全于IRAS点源表和其他巡天资料得到的结果一致。 相似文献
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本文对IRAS暗源表中4个选区内的IRAS星系的两点角相关函数,关联分维进行了计算。结果表明,所有选区内的星系呈现小角尺度上的成团。在较大角尺度上,分布可以用多级分形很好地表示。在更大角尺度上,用非归一星系对计数可以探测到密度分布中可能存在的典型尺度。当取4个选区的平均值作为IRAS星系在宇宙中分布情况的代表时,所得结果与用全天IRAS点源表和其他巡天资料得到的结果一致。 相似文献
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我们用北京天文台兴隆观测站60厘米望远镜对NGC1019等10个旋涡星系进行了CCD照相观测,通过对图象的预处理及利用彭秋和(1988年)提出的方法,得到了这10个星系盘的等值高度和星系的倾角(星系平面和天球切平面之间的夹角)等一些重要物理量. 相似文献
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《中国天文和天体物理学报》2001,1(5):395-405
RESEARCH PAPERS 1 INTRODUCTIONA spiraI gaIaxy inherently consists of a halo, a bulge and a thin disc with spiral structurewhich emerges from the central region or the end of a bright bar. Optical images of spirals, whichare projections on the celestial sphere, are dominated by the light from the stars, as modifiedby the extinction and reddening of dust. AIthough Lord Rosse first discovered that M51 hastwo spiral arms in 1845, the form of the spiral structure had not been investigat… 相似文献
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Ma Jun Zhao Jun-liang Zhang Fei-peng Peng Qiu-he 《Chinese Astronomy and Astrophysics》2000,24(4):367-443
A statistical study has been made for the variations along the Hubble sequence, os such parameters as the degree of tightness of winding of spiral arm λ, the pitch angle μ, the flatness of the disk H/D25 and the thickness H along the Hubble sequence for 365 spiral galaxies published in A&Ap Supplement Series. The mean values of these quantities for the various Hubble types have been obtained for the first time. The results of the statistics show clearly 1) that the Hubble classification of spiral galaxies is one which has only a qualitative and statistical significance, and 2) that the dispersion relation in the density wave theory is valid for most spiral galaxies, i.e., the arms of most spiral galaxies satisfy the requirements of being tightly wound. 相似文献
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Anvar Shukurov 《Astrophysics and Space Science》2002,281(1-2):285-288
We discuss the properties of the large-scale galactic magnetic fields which can help to discriminate between theories of their
origin. We argue that the mean-field dynamo theory in its simplest form is unique in that it can explain most of the known
features from a single conceptual viewpoint.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
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John F. L. Simmons Edouard Audit 《Monthly notices of the Royal Astronomical Society》2000,319(2):497-509
Scattering of starlight by dust, molecules and electrons in spiral galaxies will produce a modification of the direct intensity and a polarization in the observed light. We treat the case where the distribution of scatterers can be considered to be optically thin, and derive semi-analytic expressions for the resolved intensity and polarized intensity for Thomson, Rayleigh, and more general scattering mechanisms. These expressions are applied to a parametric model for spiral galaxies. It is further shown that in the case of Thomson and Rayleigh scattering, and when scatterers and stars are distributed with rotational symmetry, the total polarized flux depends on the inclination, i , of the galactic axis to the line of sight according to a simple sin2 i law. This generalizes the well-known result for point-like and spherical light sources. By using a method based on spherical harmonics, we generalize this law for more general mechanisms, and show that to good approximation, the sin2 i law still holds for the class of models considered. 相似文献
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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
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Annamaria Borriello Paolo Salucci 《Monthly notices of the Royal Astronomical Society》2001,323(2):285-292
We use high-quality optical rotation curves of nine low-luminosity disc galaxies to obtain the velocity profiles of the surrounding dark matter haloes. We find that they increase linearly with radius at least out to the edge of the stellar disc, implying that, over the entire stellar region, the density of the dark halo is about constant.
The properties of the mass structure of these haloes are similar to those found for a number of dwarf and low surface brightness galaxies, but provide a more substantial evidence of the discrepancy between the halo mass distribution predicted in the cold dark matter scenario and those actually detected around galaxies. We find that the density law proposed by Burkert reproduces the halo rotation curves, with halo central densities ( ρ0 ∼1–4×10−24 g cm−3 ) and core radii ( r 0 ∼5–15 kpc) scaling as ρ 0 ∝ r 0 −2/3 . 相似文献
The properties of the mass structure of these haloes are similar to those found for a number of dwarf and low surface brightness galaxies, but provide a more substantial evidence of the discrepancy between the halo mass distribution predicted in the cold dark matter scenario and those actually detected around galaxies. We find that the density law proposed by Burkert reproduces the halo rotation curves, with halo central densities ( ρ
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Sébastien Poirier Pascale Jablonka Jean-Michel Alimi 《Astrophysics and Space Science》2003,284(2):849-852
We investigate the consequences of the hypothesis of the secular evolution (growth of the bulge from disc material via a bar
and temporal evolution of the Hubble sequence) on the chemical evolution of a galaxy. We present the first dynamical and chemical
results of our 3D tree-SPH simulations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献