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1.
A three‐dimensional dynamical model for a galaxy hosting a BL Lacertae object is constructed. The model consists of a logarithmic potential representing an elliptical host galaxy with a bulge of radius cb and a dense massive nucleus. Using numerical experiments, we try to distinguish between regular and chaotic motion in both 2D and 3D system. In particular, we investigate how the basic parameters of our model, such as the mass of the nucleus, the internal perturbation and the flattening parameters influence the amount and the degree of chaos. Interesting correlations are presented for both 2D and 3D dynamical models. Our numerical results are explained and supported using elementary theoretical arguments and analytical calculations. Of particular interest is the local integral of motion which have been found to exist in the vicinity of stable periodic points. The obtained numerical outcomes of the present research are linked and also compared with several data derived from observations. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
A galaxy model with a satellite companion is used to study the character of motion for stars moving in the x ‐y plane. It is observed that a large part of the phase plane is covered by chaotic orbits. The percentage of chaotic orbits increases when the galaxy has a dense nucleus of massMn. The presence of the dense nucleus also increases the stellar velocities near the center of the galaxy. For small values of the distance R between the two bodies, low energy stars display a chaotic region near the centre of the galaxy, when the dense nucleus is present, while for larger values of R the motion in active galaxies is regular for low energy stars. Our results suggest that in galaxies with a satellite companion, the chaotic character of motion is not only a result of galactic interaction but also a result caused by the dense nucleus. Theoretical arguments are used to support the numerical outcomes. We follow the evolution of the galaxy, as mass is transported adiabatically from the disk to the nucleus. Our numerical results are in satisfactory agreement with observational data from M51‐type binary galaxies (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3.
We construct a 2D-dynamical model in order to study the motion in a galaxy with a double nucleus. Numerical calculations show that the majority of high energy stars, near the double nuclear region, are on chaotic orbits. On the contrary, low energy stars are on chaotic orbits only near massive nuclei while, for less massive nuclei, the motion is regular. Using a semi-numerical approach we explain the chaotic scattering of orbits near each nucleus. The high values of the velocities near the dense nuclei are also explained. Computation of the LCEs indicates a very high degree of chaos. The results derived from our double nucleus dynamical model are compared with models with single ones. Our outcomes are in satisfactory agreement with observational data for the double nucleus system NGC6240.  相似文献   

4.
In the present article, we use an axially symmetric galactic gravitational model with a disk–halo and a spherical nucleus, in order to investigate the transition from regular to chaotic motion for stars moving in the meridian (r,z) plane. We study in detail the transition from regular to chaotic motion, in two different cases: the time independent model and the time evolving model. In both cases, we explored all the available range regarding the values of the main involved parameters of the dynamical system. In the time dependent model, we follow the evolution of orbits as the galaxy develops a dense and massive nucleus in its core, as mass is transported exponentially from the disk to the galactic center. We apply the classical method of the Poincaré (r,pr) phase plane, in order to distinguish between ordered and chaotic motion. The Lyapunov Characteristic Exponent is used, to make an estimation of the degree of chaos in our galactic model and also to help us to study the time dependent model. In addition, we construct some numerical diagrams in which we present the correlations between the main parameters of our galactic model. Our numerical calculations indicate, that stars with values of angular momentum Lz less than or equal to a critical value Lzc, moving near to the galactic plane, are scattered to the halo upon encountering the nuclear region and subsequently display chaotic motion. A linear relationship exists between the critical value of the angular momentum Lzc and the mass of the nucleus Mn. Furthermore, the extent of the chaotic region increases as the value of the mass of the nucleus increases. Moreover, our simulations indicate that the degree of chaos increases linearly, as the mass of the nucleus increases. A comparison is made between the critical value Lzc and the circular angular momentum Lz0 at different distances from the galactic center. In the time dependent model, there are orbits that change their orbital character from regular to chaotic and vise versa and also orbits that maintain their character during the galactic evolution. These results strongly indicate that the ordered or chaotic nature of orbits, depends on the presence of massive objects in the galactic cores of the galaxies. Our results suggest, that for disk galaxies with massive and prominent nuclei, the low angular momentum stars in the associated central regions of the galaxy, must be in predominantly chaotic orbits. Some theoretical arguments to support the numerically derived outcomes are presented. Comparison with similar previous works is also made.  相似文献   

5.
The evolution of chaotic motion in a galactic dynamical model with a disk, a dense nucleus and a flat biaxial dark halo component is investigated. Two cases are studied: (i) the case where the halo component is oblate and (ii) the case where a prolate halo is present. In both cases, numerical calculations show that the extent of the chaotic regions decreases exponentially as the scale‐length of the dark halo increases. On the other hand, a linear relationship exists between the extent of the chaotic regions and the flatness parameter of the halo component. A linear relationship between the critical value of the angular momentum and the flatness parameter is also found. Some theoretical arguments to support the numerical outcomes are presented. An estimation of the degree of chaos is made by computing the Lyapunov Characteristic Exponents. Comparison with earlier work is also made (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
《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   

7.
We study the transition from regular to chaotic motion in a prolate elliptical galaxy dynamical model with a bulge and a dense nucleus.Our numerical investigation shows that stars with angular momentum Lz less than or equal to a critical value Lzc,moving near the galactic plane,are scattered to higher z,when reaching the central region of the galaxy,thus displaying chaotic motion.An inverse square law relationship was found to exist between the radius of the bulge and the critical value Lzc of the angular m...  相似文献   

8.
The behavior of the orbits in a galaxy model composed of an harmonic core and a strong bar potential is studied. Numerical calculations show that a large number of orbits display chaotic motion. These orbits are low angular momentun orbits. The percentage of chaotic orbits increases as the angular velocity of the system increases or the strength of the harmonic term decreases. A new dynamical parameter, the S(c) spectrum, is introduced and used to detect the island motion and the evolution of the sticky regions. Comparison to previously obtained results reveals the leading role of the new spectrum. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
We use a composite galaxy model consisting of a disk-halo, bulge, nucleus and dark-halo components in order to investigate the motion of stars in ther-z plane. It is observed that high angular momentum stars move in regular orbits. The majority of orbits are box orbits. There are also banana-like orbits. For a given value of energy, only a fraction of the low angular momentum stars — those going near the nucleus — show chaotic motion while the rest move in regular orbits. Again one observes the above two kinds of orbits. In addition to the above one can also see orbits with the characteristics of the 2/3 and 3/4 resonance. It is also shown that, in the absence of the bulge component, the area of chaotic motion in the surface of section increases, significantly. This suggests that a larger number of low angular momentum stars are in chaotic orbits in galaxies with massive nuclei and no bulge components.  相似文献   

10.
A new method for classification of galaxy spectra is presented, based on a recently introduced information theoretical principle, the information bottleneck . For any desired number of classes, galaxies are classified such that the information content about the spectra is maximally preserved. The result is classes of galaxies with similar spectra, where the similarity is determined via a measure of information. We apply our method to ∼6000 galaxy spectra from the ongoing 2dF redshift survey, and a mock-2dF catalogue produced by a cold dark matter (CDM) based semi-analytic model of galaxy formation. We find a good match between the mean spectra of the classes found in the data and in the models. For the mock catalogue, we find that the classes produced by our algorithm form an intuitively sensible sequence in terms of physical properties such as colour, star formation activity, morphology, and internal velocity dispersion. We also show the correlation of the classes with the projections resulting from a principal component analysis.  相似文献   

11.
We investigate the regular and chaotic motion in a model potential found using the recent developments of the Inverse Problem of Dynamics. The potential describes the motion in the central parts of a barred galaxy. In the absence of rotation chaotic motion is observed when the perturbation strength is near the escape perturbation for a fixed value of the energy. In the rotating cases one observes that the area of chaotic motion on the surface of section decreases as the angular velocity Ω increases and finally all orbits become regular. The character of motion is also checked by computing the Liapunov characteristic exponents in all cases. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

12.
We investigate current problems connected with the formation of cD galaxies. The subject of the present paper is to compare internal properties of the cD galaxy Zw162010 with cluster properties of Abell 1795. This consideration is a first attempt to find commonly valid essential correlations between peculiarities of brightest cluster members as structures and active phenomena and global cluster properties as for instance galaxy populations and concentration degrees. The colours, the X-ray emission, and the velocity of the cD galaxy are used to discuss the obvious influence of the environment on the evolution of the active nucleus. In a second paper (Kirchner et al. 1992) the radio structure is used to investigate the influence of the surrounding cluster medium onto the development of the active nucleus. Furtheron, various jet ejection scenarios will be quantitatively examined.  相似文献   

13.
In the present article, we present a new gravitational galactic model, describing motion in elliptical as well as in disk galaxies, by suitably choosing the dynamical parameters. Moreover, a new dynamical parameter, the S(g) spectrum, is introduced and used, in order to detect islandic motion of resonant orbits and the evolution of the sticky regions. We investigate the regular or chaotic character of motion, with emphasis in the different dynamical models and make an extensive study of the sticky regions of the system. We use the classical method of the Poincaré r ? pr phase plane and the new dynamical parameter of the S(g) spectrum. The L.C.E is used, in order to make an estimation of the degree of chaos in our galactic model. In both cases, the numerical calculations, suggest that our new model, displays a wide variety of families of regular orbits, compared to other galactic models. In addition to the regular motion, this new model displays also chaotic regions. Furthermore, the extent of the chaotic regions increases, as the value of the flatness parameter b of the model increases. Moreover, our simulations indicate, that the degree of chaos in elliptical galaxies, is much smaller than that in dense disk galaxies. In both cases numerical calculations show, that the degree of chaos increases linearly, as the flatness parameter b increases. In addition, a linear relationship between the critical value of angular momentum and the b parameter if found, in both cases (elliptical and disk galaxies). Some theoretical arguments to support the numerical outcomes are presented. Comparison with earlier work is also made.  相似文献   

14.
We study the regular or chaotic character of orbits in a 3D dynamical model,describing a triaxial galaxy surrounded by a spherical dark halo component.Our numerical experiments suggest that the percentage of chaotic orbits decreases exponentially as the mass of the dark halo increases.A linear increase of the percentage of the chaotic orbits was observed as the scale length of the halo component increases. In order to distinguish between regular and chaotic motion,we chose to use the total angular momentum ...  相似文献   

15.
NGC 1365     
Summary. The aim of the present review is to give a global picture of the supergiant barred galaxy NGC 1365. This galaxy with its strong bar and prominent spiral structure displays a variety of nuclear activity and ongoing star formation. The kinematics of the galaxy has been mapped in detail by optical long slit and Fabry–Perot observations as well as radio observations of Hi and CO interstellar lines. From these observations a combined velocity field has been derived, describing the circulation of interstellar gas in the symmetry plane of the galaxy. With a gravitational potential based on near infrared photometry of the bar and the shape of the apparent rotation curve, computer simulations of the dynamics of the interstellar gas have been made with the aim to reproduce both the morphology of the interstellar matter as well as the observed velocity field. The simulations demonstrate the role of the bar and the importance of resonances between the bar rotation and the rotation of the galaxy for the formation of the spiral structure. Polarization of radio radiation reveals magnetic fields concentrated to the dust lanes along and across the bar, where they are aligned with the flow pattern of the gas, and along the spiral arms. The kinematics of the outer region of the galaxy with a fairly unique decline of the rotation curve leads to the conclusion that NGC 1365 lacks a very massive dark matter halo, which may permit the formation of a very strong bar. The galaxy contains an active nucleus with both broad and narrow components of the permitted spectral emission lines. The nucleus is surrounded by a molecular torus, numerous star forming regions and continuum radio sources. The star forming regions are, as seen with the Hubble Space Telescope (HST), resolved into a large number of super star clusters suggested to be young globular clusters. A very compact radio source, seen at high spatial resolution with the Very Large Array (VLA), has been claimed to coincide with one of the super star clusters. This compact source has a radio brightness of the order of 100 times that of the bright galactic supernova remnant Cas A and is suggested to be a so called ‘radio supernova’. Two other such compact radio sources, positioned in the prominent dark dust lane penetrating the nuclear region, are identified as strong infrared sources by observations with the Very Large Telescope (VLT). The cause of this infrared radiation may be dust heated by the objects that drive the radio sources. The X-ray radiation from the nucleus is interpreted to consist of hard continuum radiation from the active nucleus itself, Fe-K line emission from a rotating disk, and thermal emission from the surrounding star burst activity. A secondary, highly variable source has been discovered close to the nuclear region. It seems to be one of the most luminous and most highly variable off-nuclear X-ray sources known. The higher excitation optical emission lines in the nuclear region, primarily from [Oiii], reveal a velocity field quite different from that described by the galactic rotation. The deviating [Oiii] morphology and velocity field in the nuclear region is interpreted in terms of a high excitation outflow double-cone with its apex at the nucleus and symmetry axis perpendicular to the symmetry plane of the galaxy. One of the circumnuclear radio sources seems to be a one-sided jet emerging from the nucleus aligned with the cone axis. According to the model, the outward flow within the cone is accelerated and the flow velocity highest at the cone axis. Received 15 January 1999  相似文献   

16.
We use a simple dynamical model which consists of a harmonic oscillator and a spherical component, in order to investigate the regular or chaotic character of orbits in a barred galaxy with a central spherically symmetric nucleus. Our aim is to explore how the basic parameters of the galactic system influence the nature of orbits, by computing in each case the percentage of chaotic orbits, as well as the percentages of different types of regular orbits. We also give emphasis to the types of regular orbits that support either the formation of nuclear rings or the barred structure of the galaxy. We provide evidence that the traditional x1 orbital family does not always dominate in barred galaxy models since we found several other types of resonant orbits which can also support the barred structure. We also found that sparse enough nuclei, fast rotating bars and high energy models can support the galactic bars. On the other hand, weak bars, dense central nuclei, slowly rotating bars and low energy models favor the formation of nuclear rings.We also compare our results with previous related work.  相似文献   

17.
We present radio observations and optical spectroscopy of the giant low surface brightness (LSB) galaxy PGC 045080 (or 1300+0144). PGC 045080 is a moderately distant galaxy having a highly inclined optical disc and massive H  i gas content. Radio continuum observations of the galaxy were carried out at 320, 610 MHz and 1.4 GHz. Continuum emission was detected and mapped in the galaxy. The emission appears extended over the inner disc at all three frequencies. At 1.4 GHz and 610 MHz it appears to have two distinct lobes. We also did optical spectroscopy of the galaxy nucleus; the spectrum did not show any strong emission lines associated with active galactic nucleus (AGN) activity but the presence of a weak AGN cannot be ruled out. Furthermore, comparison of the Hα flux and radio continuum at 1.4 GHz suggests that a significant fraction of the emission is non-thermal in nature. Hence we conclude that a weak or hidden AGN may be present in PGC 045080. The extended radio emission represents lobes/jets from the AGN. These observations show that although LSB galaxies are metal poor and have very little star formation, their centres can host significant AGN activity. We also mapped the H  i gas disc and velocity field in PGC 045080. The H  i disc extends well beyond the optical disc and appears warped. In the H  i intensity maps, the disc appears distinctly lopsided. The velocity field is disturbed on the lopsided side of the disc but is fairly uniform in the other half. We derived the H  i rotation curve for the galaxy from the velocity field. The rotation curve has a flat rotation speed of ∼190 km s−1.  相似文献   

18.
The problem of the change in gravitational energy of a colliding galaxy due to tidal effects is considered. The change in the internal energy, the mass of escaping matter and the change in the mean radius of the test galaxy have been estimated for a relative velocity of 1000 km s–1 for three distances of closest approach for the following four cases: (a) both galaxies centrally concentrated, (b) both galaxies homogeneous, (c) test galaxy centrally concentrated, field galaxy homogeneous, and (d) test galaxy homogeneous, field galaxy centrally concentrated. The masses and radii of the two galaxies are taken as 1011 M and 10 kpc respectively. For simplicity, the galaxies are assumed to be spherically symmetric and the distribution of mass within a centrally concentrated galaxy is assumed to be that of a polytrope of indexn=4. The results also provide estimates for the minimum relative velocity a galaxy must have in order that it may not be captured by another to form a double system. It has been found that normally a relative velocity of less than about 500 km s–1 will lead to the formation of a double galaxy by tidal capture. In the case of a head-on collision between two centrally concentrated galaxies even a relative velocity of about 1000 km s–1 is small enough for tidal capture. The changes in the structure of the galaxies for relative velocities equal to velocity of escape are also indicated. These results show that there is no escape of matter from the test galaxy in cases (b) and (c). In the case (a) the escape of matter can be as high as 4% of the total mass. The head-on collision between galaxies are normally not accompanied by any escape of matter. All the gain in the internal energy of galaxies during such collisions results in increase in their dimensions. The fractional increase in the mean radius of the test galaxy in the head-on collision is 1.5 in the case (a), 3.2 in the case (b) and 0.01 in the case (c). In the case (d) the test galaxy will be disrupted by the tidal forces.  相似文献   

19.
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   

20.
We use probability density functions (pdfs) of sums of orbit coordinates, over time intervals of the order of one Hubble time, to distinguish weakly from strongly chaotic orbits in a barred galaxy model. We find that, in the weakly chaotic case, quasi-stationary states arise, whose pdfs are well approximated by q-Gaussian functions (with 1 <?q < 3), while strong chaos is identified by pdfs which quickly tend to Gaussians (q =?1). Typical examples of weakly chaotic orbits are those that ??stick?? to islands of ordered motion. Their presence in rotating galaxy models has been investigated thoroughly in recent years due to their ability to support galaxy structures for relatively long time scales. In this paper, we demonstrate, on specific orbits of 2 and 3 degree of freedom barred galaxy models, that the proposed statistical approach can distinguish weakly from strongly chaotic motion accurately and efficiently, especially in cases where Lyapunov exponents and other local dynamic indicators appear to be inconclusive.  相似文献   

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