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1.
A. D. Chemin 《Astrophysics》1998,41(4):399-407
A phenomenon discovered by Vorontsov-Vel’yaminov — straight segments in the spiral structure of giant galaxies — is studied.
The main geometrical and physical characteristics of these structures are demonstrated using the example of the galaxies M101
and especially M51. It is shown that rows alternate with regular spiral arms over almost their entire extent in M101, M51,
and a number of other galaxies. The relationship between rows and straight warm dust lanes at the inner edges of spiral arms
is traced. Assuming these dust lanes to be gas layers compressed by a spiral shock wave, the possibility that rows are formed
in local segments of the spiral shock front that are being flattened is discussed. New observational facts about rows support
the quantitative consequences of this gasdynamical picture.
Translated from Astrofizika, Vol. 41. No. 4, pp. 609–622, October–December, 1998. 相似文献
2.
Arthur D. Chernin 《Monthly notices of the Royal Astronomical Society》1999,308(2):321-332
The phenomenon of 'rows', which are straight geometrical segments in the spiral arms of galaxies, is studied. The Whirlpool nebula, Messier 51 (NGC 5194) in Canes Venatici, is considered to be an example of a giant grand design galaxy. Optical photographs, H α , ultraviolet and far-ultraviolet images, CO, 21-cm and synchrotron emission maps, and a K s -band mosaic of M51 are studied. With this observational material, multiple rows can be recognized in the spiral arms of the galaxy. The rows comprise a major part of the arms. The lengths of the rows increase almost linearly with distance from the centre. They intersect one another at an (average) angle ≈2π/3. A possible physical explanation of the phenomenon of rows is discussed on the basis of the assumption that the formation of straight arm segments might be due to the gas-dynamical effect of stability of flat shock fronts, and the tendency of a slightly curved shock front to become flat. A quantitative flattening criterion enables an explanation of the geometrical properties of the arm patterns found in M51 and also in M101. A brief list of spirals with rows is given. 相似文献
3.
Galaxies with “rows” in Vorontsov-Velyaminov’s terminology stand out among the variety of spiral galactic patterns. A characteristic feature of such objects is the sequence of straight-line segments that forms the spiral arm. In 2001 A. Chernin and co-authors published a catalog of such galaxies which includes 204 objects from the Palomar Atlas. In this paper, we supplement the catalog with 276 objects based on an analysis of all the galaxies from the New General Catalogue and Index Catalogue. The total number of NGC and IC galaxies with rows is 406, including the objects of Chernin et al. (2001). The use of more recent galaxy images allowed us to detect more “rows” on average, compared with the catalog of Chernin et al. When comparing the principal galaxy properties we found no significant differences between galaxies with rows and all S-typeNGC/IC galaxies.We discuss twomechanisms for the formation of polygonal structures based on numerical gas-dynamic and collisionless N-body calculations, which demonstrate that a spiral pattern with rows is a transient stage in the evolution of galaxies and a system with a powerful spiral structure can pass through this stage. The hypothesis of A. Chernin et al. (2001) that the occurrence frequency of interacting galaxies is twice higher among galaxies with rows is not confirmed for the combined set of 480 galaxies. The presence of a central stellar bar appears to be a favorable factor for the formation of a system of “rows”. 相似文献
4.
The results of numerical simulations of a gaseous disk in the potential of a stellar spiral density wave are presented. The
conditions under which straightened spiral arm segments (rows) form in the gas component are studied. These features of the
spiral structure were identified in a series of works by A.D. Chernin with coauthors. Gas-dynamic simulations have been performed
for a wide range of model parameters: the pitch angle of the spiral pattern, the amplitude of the stellar spiral density wave,
the disk rotation speed, and the temperature of the gas component. The results of 2D- and 3D-disk simulations are compared.
The rows in the numerical simulations are shown to be an essentially nonstationary phenomenon. A statistical analysis of the
distribution of geometric parameters for spiral patterns with rows in the observed galaxies and the constructed hydrodynamic
models shows good agreement. In particular, the numerical simulations and observations of galaxies give 〈α〉 }~ 120° for the
average angles between straight segments. 相似文献
5.
J. H. Piddington 《Astrophysics and Space Science》1978,59(1):237-256
Theories of galactic structure are reviewed briefly before comparing them with recent observations. Also reviewed is the evidence for an intergalactic magnetic field and its possible effects on gas concentrations and patterns of star creation, including spiral arms. It is then shown that normal spiral galaxies may be divided into the M51-type and others. The rare M51-type have Hi gas arms coincident with unusually filamentary and luminous optical arms; they also have a companion galaxy. The remaining great majority of spirals have no well-defined gas arms and their optical arms are irregular, broader and less luminous; they have no companion galaxy. It appears that without exception the half-dozen or so galaxies whose structures appear to support the density-wave theory show one or more of the characteristics of the rare type of spiral, and that the three principal confirmations of the spiral-wave idea (M51, M81, M101) have companions which may account for their arms. Toomre has rejected this idea on the grounds that his models do not agree with the observed structures. It is shown that these models are inadequate in two major respects, and when replaced by magneto-tidal models using non-uniform gas disks one might expect agreement. The original hydromagnetic model of spiral arms is now reserved for non-interacting galaxies, of which M33 might be taken as a prototype. The model predicts broad or massive optical arms and no corresponding arms of neutral hydrogen, as observed. 相似文献
6.
晚型星系金属丰度与自转速度的关系 总被引：1，自引：0，他引：1
星系物质化学组成的研究不仅对于理解有关星系形成和演化的各种物理过程具有重要意义，而且还可以对星系形成和演化的各种理论模型提供重要的约束。随着观测技术及理论工作水平的不断提高，利用星系的大量观测资料来系统地研究星系化学组成与星系宏观性质之间的关系将成为可能。星系金属丰度与光度之间的强相关性以及晚型星系金属丰度与自转速度的关系即是其中最有意义的内容之一。全面回顾了星系金属丰度与星系宏观观测性质间关系的研究历史，重点评述了晚型星系金属丰度与自转速度关系的最新研究进展，详细讨论了目前对此类关系的物理解释及其对星系形成和演化模型的影响。 相似文献
7.
利用星系解构软件GALFIT通过面亮度轮廓拟合对近邻早型旋涡星系M81 (NGC 3031)进行形态学解构,旨在探究M81星系的结构组成并对其进行形态学量化.通过6种解构模式,对M81进行了不同复杂程度的结构分解,其中最复杂的解构模式包含核球、盘、外旋臂、内旋臂、星系核5个子结构.研究结果显示, M81有一个Sérsic指数约为5.0的经典核球,其形态和光度在不同解构模式中均保持稳定; M81星系盘的Sérsic指数约为1.2,但它的形态参数和光度与是否分解内旋臂相关.不同子结构的组合对作为混合体的星系整体的形态有不可忽视的影响.星系解构的结果提供了不同解构模式适用性的建议:其中核球+盘+星系核的三成分解构适用于大样本星系的核-盘研究;而考虑旋臂的复杂解构则适合于对星系子结构的精确测量,如小样本(或个源)研究.基于Spitzer-The Infrared Array Camera (IRAC) 4.5μm的单波段图像的形态学解构研究是后续一系列研究的开始,在此基础上未来将会对M81进行多波段解构,同时研究不同子结构的光谱能量分布和星族性质,并推断M81各子结构的形成历史和演化过程. 相似文献
8.
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
9.
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
10.
《New Astronomy》2014
Most rapidly and differentially rotating disk galaxies, in which the sound speed (thermal velocity dispersion) is smaller than the orbital velocity, display graceful spiral patterns. Yet, over almost 240 yr after their discovery in M51 by Charles Messier, we still do not fully understand how they originate. In this first paper of a series, the dynamical behavior of a rotating galactic disk is examined numerically by a high-order Godunov hydrodynamic code. The code is implemented to simulate a two-dimensional flow driven by an internal Jeans gravitational instability in a nonresonant wave–“fluid” interaction in an infinitesimally thin disk composed of stars or gas clouds. A goal of this work is to explore the local and linear regimes of density wave formation, employed by Lin, Shu, Yuan and many others in connection with the problem of spiral pattern of rotationally supported galaxies, by means of computer-generated models and to compare those numerical results with the generalized fluid-dynamical wave theory. The focus is on a statistical analysis of time-evolution of density wave structures seen in the simulations. The leading role of collective processes in the formation of both the circular and spiral density waves (“heavy sound”) is emphasized. The main new result is that the disk evolution in the initial, quasilinear stage of the instability in our global simulations is fairly well described using the local approximation of the generalized wave theory. Certain applications of the simulation to actual gas-rich spiral galaxies are also explored. 相似文献
11.
Nelson D. Padilla Michael A. Strauss 《Monthly notices of the Royal Astronomical Society》2008,388(3):1321-1334
We determine the underlying shapes of spiral and elliptical galaxies in the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) from the observed distribution of projected galaxy shapes, taking into account the effects of dust extinction and reddening. We assume that the underlying shapes of spirals and ellipticals are well approximated by triaxial ellipsoids. The elliptical galaxy data are consistent with oblate spheroids, with a correlation between luminosity and ellipticity: the mean values of minor to middle axis ratios are 0.41 ± 0.03 for M r ≈−18 ellipticals and 0.76 ± 0.04 for M r ≈−22.5 ellipticals. Ellipticals show almost no dependence of axial ratio on galaxy colour, implying a negligible dust optical depth.
There is a strong variation of spiral galaxy shapes with colour indicating the presence of dust. The intrinsic shapes of spiral galaxies in the SDSS DR6 are consistent with flat discs with a mean and dispersion of thickness to diameter ratio of (21 ± 2) per cent, and a face-on ellipticity, e , of ln( e ) =−2.33 ± 0.79 . Not including the effects of dust in the model leads to discs that are systematically rounder by up to 60 per cent. More luminous spiral galaxies tend to have thicker and rounder discs than lower luminosity spirals. Both elliptical and spiral galaxies tend to be rounder for larger galaxies.
The marginalized value of the edge-on r -band dust extinction E0 in spiral galaxies is E 0 ≃ 0.45 mag for galaxies of median colours, increasing to E 0 = 1 mag for g − r > 0.9 and E 0 = 1.9 for the luminous and most compact galaxies, with half-light radii <2 h −1 kpc . 相似文献
There is a strong variation of spiral galaxy shapes with colour indicating the presence of dust. The intrinsic shapes of spiral galaxies in the SDSS DR6 are consistent with flat discs with a mean and dispersion of thickness to diameter ratio of (21 ± 2) per cent, and a face-on ellipticity, e , of ln( e ) =−2.33 ± 0.79 . Not including the effects of dust in the model leads to discs that are systematically rounder by up to 60 per cent. More luminous spiral galaxies tend to have thicker and rounder discs than lower luminosity spirals. Both elliptical and spiral galaxies tend to be rounder for larger galaxies.
The marginalized value of the edge-on r -band dust extinction E
12.
On the basis of Poisson＇s equation for the logarithmic perturbation of matter density, we provide improved estimates of scale heights and spiral structures for non-edge-on spiral galaxies by subtracting the surface brightness distributions from observed images. As examples, the non-edge-on spiral galaxies PGC 24996, which is face-on, and M31, which is inclined, are studied. The scale height, pitch angle and inclination angle of M31, our nearest neighbor, that are presented in this work, agree well with previous research. 相似文献
13.
A study of collisions between spiral and elliptical galaxies (approximated as composite spherical masses) is made to assess the changes undergone by the elliptical. Results indicate that unless the spiral is extremely massive compared to the elliptical, the elliptical is almost unaffected, while the spiral is strongly affected. For the frequent type of collision between equally massive spiral and elliptical galaxies, the elliptical is negligibly affected, while disruptive effects set in the spiral. However, the stellar pattern of the elliptical is changed and the stars are found to crowd in faint shells after the collision. The consequences of these results are explored in the context of the morphology-density relationship and the elliptical companions of ring galaxies. 相似文献
14.
We describe gravitationalN-body simulations to investigate whether various non-Newtonian interactions between the stars of a system could explain the flat rotational curves which are characteristic of actual isolated spiral galaxies. It is shown that replacing the standard Newtonian interaction by the models of Sanders (1984), Kuhn and Kruglyak (1987) and Milgrom (1983), no massive halo (or dark matter) is required to produce the flat rotational curves of the systems under consideration. All models also generate the exponential surface mass density distribution which is in agreement with that observed in disk-shaped galaxies. In relation to the spiral structure of galaxies, we present the evidence that the non-Newtonian interactions can reproduce the multiple armed patterns in stellar disks without dark matter. 相似文献
15.
Rainer Beck 《Astrophysics and Space Science》2009,320(1-3):77-84
Spiral galaxies host dynamically important magnetic fields which can affect gas flows in the disks and halos. Total magnetic fields in spiral galaxies are strongest (up to 30 μG) in the spiral arms where they are mostly turbulent or tangled. Polarized synchrotron emission shows that the resolved regular fields are generally strongest in the interarm regions (up to 15 μG). Faraday rotation measures of radio polarization vectors in the disks of several spiral galaxies reveal large-scale patterns which are signatures of coherent fields generated by a mean-field dynamo. Magnetic fields are also observed in radio halos around edge-on galaxies at heights of a few kpc above the disk. Cosmic-ray driven galactic winds transport gas and magnetic fields from the disk into the halo. The halo scale height and the electron lifetime allow to estimate the wind speed. The magnetic energy density is larger than the thermal energy density, but smaller than the kinetic energy density of the outflow. There is no observation yet of a halo with a large-scale coherent dynamo pattern. A global wind outflow may prevent the operation of a dynamo in the halo. Halo regions with high degrees of radio polarization at very large distances from the disk are excellent tracers of interaction between galaxies or ram pressure of the intergalactic medium. The observed extent of radio halos is limited by energy losses of the cosmic-ray electrons. Future low-frequency radio telescopes like LOFAR and the SKA will allow to trace halo outflows and their interaction with the intergalactic medium to much larger distances. 相似文献
16.
We have determined a dust-free colour–magnitude (CM) relation for spiral galaxies, by using I − K colours in edge-on galaxies above the plane. We find that the scatter in this relation is small and approximately as large as can be explained by observational uncertainties. The slope of the near-IR CM relation is steeper for spirals than for elliptical galaxies. We suggest two possible explanations. First, the difference could be caused by vertical colour gradients in spiral galaxies. In that case these gradients should be similar for all galaxies, on average ∼0.15 dex in [Fe/H] per scaleheight, and should increase for later galaxy types. The most likely explanation, however, is that spirals and ellipticals have intrinsically different CM relations. This means that the stars in spirals are younger than those in ellipticals. The age, however, or the fraction of young stars in spiral galaxies would be determined solely by the luminosity of the galaxy, and not by its environment. 相似文献
17.
J. H. Piddington 《Astrophysics and Space Science》1974,31(1):225-240
It is confirmed that the creation of stars in spiral (and perhaps also Irri) galaxies requires a physical parameter (X factor) additional to gas density. Consequently theX factor is an essential feature of stellar patterns and perhaps of stellar systems (spiral and other disk and spheroidal systems, globular clusters) and may be the key to the origin of the few, yet remarkably varied Hubble system of galaxies.
- It is shown that theX factor is organized over the whole galaxy and is a function of azimuth φ as well as radiusr. Only a galaxy-wide force field seems capable of explaining such anX(r, φ) factor either magnetic or gravitational in origin.
- If gravitational in origin, theX factor must be a shock wave, but a survey of observations in eight galaxies, including our own, shows no large-scale shocks associated with star creation. This provides further strong evidence against the density-shock theory of twin spiral arms.
- It is confirmed that galaxies of different Hubble types did not evolve from one another, so that each protogalaxy must possess a genetic factor which predetermines its evolution, and in particular its stellar systems. Thus the protogalactic genetic factor may be identical with theX factor.
- The case for a primordial magnetic field is strengthened, and it is shown that in our Galaxy and some others the field must be generally oblique to the disk. Such a field can explain theX(r, φ) factor in terms of a magneto-gravitational mechanism of gas clumping.
- An earlier, hydromagnetic theory of the Hubble types and of radio galaxies is extended by including theX factor to explain the various stellar systems observed in spiral, elliptical, lenticular and irregular galaxies.
18.
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
19.
Harry I. Ringermacher Lawrence R. Mead 《Monthly notices of the Royal Astronomical Society》2009,397(1):164-171
We describe a new formula capable of quantitatively characterizing the Hubble sequence of spiral galaxies including grand design and barred spirals. Special shapes such as ring galaxies with inward and outward arms are also described by the analytic continuation of the same formula. The formula is r (φ) = A /log [ B tan (φ/2 N )] . This function intrinsically generates a bar in a continuous, fixed relationship relative to an arm of arbitrary winding sweep. A is simply a scale parameter while B , together with N , determines the spiral pitch. Roughly, greater N results in tighter winding. Greater B results in greater arm sweep and smaller bar/bulge, while smaller B fits larger bar/bulge with a sharper bar/arm junction. Thus B controls the 'bar/bulge-to-arm' size, while N controls the tightness much like the Hubble scheme. The formula can be recast in a form dependent only on a unique point of turnover angle of pitch – essentially a one-parameter fit, aside from a scalefactor. The recast formula is remarkable and unique in that a single parameter can define a spiral shape with either constant or variable pitch capable of tightly fitting Hubble types from grand design spirals to late-type large barred galaxies. We compare the correlation of our pitch parameter to Hubble type with that of the traditional logarithmic spiral for 21 well-shaped galaxies. The pitch parameter of our formula produces a very tight correlation with ideal Hubble type suggesting it is a good discriminator compared to logarithmic pitch, which shows poor correlation here similar to previous works. Representative examples of fitted galaxies are shown. 相似文献
20.
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