共查询到20条相似文献，搜索用时 31 毫秒
1.
L. Morelli A. Pizzella E. M. Corsini E. Dalla Bont L. Coccato J. Mndez‐Abreu M. Parmiggiani 《Astronomische Nachrichten》2015,336(2):208-219
Key information to understand the formation and evolution of disk galaxies are imprinted in the stellar populations of their bulges. This paper has the purpose to make available new measurements of the stellar population properties of the bulges of four spiral galaxies. Both the central values and radial profiles of the line strength of some of the most common Lick indices are measured along the major‐ and minor‐ axis of the bulge‐dominated region of the sample galaxies. The corresponding age, metallicity, and α /Fe ratio are derived by using the simple stellar population synthesis model predictions. The central values and the gradients of the stellar population properties of ESO‐LV 1890070, ESO‐LV 4460170, and ESO‐LV 5140100 are consistent with previous findings for bulges of spiral galaxies. On the contrary, the bulge of ESO‐LV 4500200 shows peculiar chemical properties possibly due to the presence of a central kinematically‐decoupled component. The negative metallicity gradient found in our bulges sample indicates a relevant role for the dissipative collapse in bulge formation. However, the shallow gradients found for the age and α /Fe ratio suggests that merging can not be completely ruled out for the sample bulges. This is confirmed by the properties of ESO‐LV 4500200 which can hardly be explained without invoking the capture of external material. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
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
3.
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
4.
5.
The study of rotation curves is the most powerful tool for determining mass distributions inside spiral galaxies. Since the first trial by Burbidgeet al. (1959), followed by Brandt (1960), few methods have been proposed for the determination of the masses of galaxies (Faber and Gallagher, 1979). Monnet and Simien (1977) recently proposed a method based on a two component model (bulge and disk) which permits to compute the total mass providing that the photometry is well-known. We suggest here a method based on a new simple parametrization of the optical rotation curve. This method indicates disk masses substantially higher than the provious estimates and suggests an exponential increase of theM/L ratio in the disk toward the outer parts of the Galaxies. 相似文献
6.
Masafumi Noguchi 《Monthly notices of the Royal Astronomical Society》2001,328(2):353-358
It is shown that the giant low surface brightness galaxies (GLSBs), characterized by a large but diffuse disc component, can result from ordinary spiral galaxies through dynamical evolution. Numerical simulations indicate that the formation of a bar in a gravitationally unstable disc with high surface density induces non-circular motions and radial mixing of disc matter, leading to the flattening of the disc density profile. The resulting decrease in the disc central surface brightness is ∼1.5 magnitude, while the disc scalelength is nearly doubled, transforming a typical high surface brightness galaxy to a GSLB. This scenario seems promising especially for the GSLBs possessing a significant bulge, which are difficult to incorporate into the traditional Hubble sequence. Namely, because this disc transmutation can operate even if a moderate bulge component exists, the GSLBs with a bulge are argued to have resulted from the high surface brightness galaxies which had already possessed a bulge. The current picture naturally explains other observed characteristics of the GSLBs as well, including the propensity for having grand-design spiral arms and a bar, a high incidence of active nuclei, and galaxy environments. 相似文献
7.
The saturation conditions for bending modes in inhomogeneous thin stellar disks that follow from an analysis of the dispersion relation are compared with those derived from N-body simulations. In the central regions of inhomogeneous disks, the reserve of disk strength against the growth of bending instability is smaller than that for a homogeneous layer. The spheroidal component (a dark halo, a bulge) is shown to have a stabilizing effect. The latter turns out to depend not only on the total mass of the spherical component, but also on the degree of mass concentration toward the center. We conclude that the presence of a compact (not necessarily massive) bulge in spiral galaxies may prove to be enough to suppress the bending perturbations that increase the disk thickness. This conclusion is corroborated by our N-body simulations in which we simulated the evolution of near-equilibrium, but unstable finite-thickness disks in the presence of spheroidal components. The final disk thickness at the same total mass of the spherical component (dark halo + bulge) was found to be much smaller than that in the simulations where a concentrated bulge is present. 相似文献
8.
David Merritt Laura Ferrarese 《Monthly notices of the Royal Astronomical Society》2001,320(3):L30-L34
We analyse a sample of 32 galaxies for which a dynamical estimate of the mass of the hot stellar component, M bulge , is available. For each of these galaxies, we calculate the mass of the central black hole, M • , using the tight empirical correlation between M • and bulge stellar velocity dispersion. The frequency function is reasonably well described as a Gaussian with and standard deviation ∼0.45; the implied mean ratio of black hole mass to bulge mass is a factor of ∼5 smaller than generally quoted in the literature. We present marginal evidence for a lower, average black hole mass fraction in more massive galaxies. The total mass density in black holes in the local Universe is estimated to be ∼ consistent with that inferred from high-redshift active galactic nuclei. 相似文献
9.
A fully three-dimensional (3D) MHD model is applied to simulate the evolution of large-scale magnetic field in galaxies interacting
with the intra-cluster medium (ICM). As the model input we use a time dependent velocity field of gas clouds (HI) resulting
from 3D N-body sticky-particle model of a galaxy. These clouds are affected by ram pressure due to their rapid motion through
the ICM. The gas evolves in an analytically given gravitational potential which includes a dark matter halo, a disk, and a
bulge component. We found that due to the interaction with the ICM the resultant magnetic field correctly reproduces the observed
structures of the magnetic field forming peculiar spiral arms and magnetic features widely observed in cluster spiral galaxies.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
10.
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
11.
Masanori Iye Tatsuo Ueda Masafumi Noguchi Shinko Aoki 《Astrophysics and Space Science》1983,89(2):363-376
A new scheme has been devised to calculate discrete unstable global shearing spiral modes of gaseous disk models of galaxies. The scheme makes use of the Legendre expansion of eigen functions and the problem of stability analysis is reduced to an eigenvalue problem of an infinite matrix. The spiral patterns of these shearing wave solutions of linearized equations change their form in the course of time due to the differential rotation of the equilibrium disk. These shearing wave solutions are presumed to have intermediate characteristics between so-called density-waves and material arms. Comparison between these shearing modes and the non-shearing normal modes for a series of disk models is presented. 相似文献
12.
The linear theory and N-body simulations are used to present a new, alternative model of the galaxy A0035-324 (the “Cartwheel”), which is the most
striking example of the relatively small class of ring galaxies. The model is based on the gravitational Jeans-type instability
of both axisymmetric (radial) and nonaxisymmetric (spiral) small-amplitude gravity perturbations (e.g., those produced by
spontaneous disturbances) of a dynamically cold subsystem (identified as the gaseous component) of an isolated disk galaxy.
The simplified model of a galaxy is used in which stars (and a dark matter, if it exists at all) do not participate in the
disk collective oscillations and just form a background charge. In the theory presented here, a case for both purely radial
solutions and purely spiral solutions to the equations of motion of an infinitesimally thin gaseous disk is made, which is
associated with both a radial density wave and a dominant spiral density wave which propagate outwards creating a rough ring
and a number of spiral arms. Through three-dimensional numerical simulation of a collisionless set of many particles, I associate
these gravitationally unstable axisymmetric waves and nonaxisymmetric waves with growing clumps of matter which take on the
appearance of a ring and spokes of mass blobs. 相似文献
13.
14.
J.C. Vega Beltrán E. Pignatelli W.W. Zeilinger A. Pizzella E.M. Corsini F. Bertola J.E. Beckman 《Astrophysics and Space Science》2001,276(2-4):509-516
We present a comparison between the ionized gas and stellar kinematics for a sample of five early-to-intermediate disc galaxies.
We measured the major axis V and σ radial profiles for both gas and stars, and the h
3 and h
4 radial profiles of the stars. We also derived from the R-band surface photometry of each galaxy the light contribution of their bulges and discs. In order to investigate the differences
between the velocity fields of the sample galaxies we adopted the self-consistent dynamical model by Pignatelli and Galletta
(1999), which takes into account the asymmetric drift effects, the projection effects along the line of sight and the non-Gaussian
shape of the line profiles due to the presence of different components with distinct dynamical behaviour. We find for the
stellar component a sizeable asymmetric drift effect in the inner regions of all the sample galaxies, as results from comparing
their stellar rotation curves with the circular velocity predicted by the models. The galaxy sample is not wide enough to
draw general conclusions. However, we have found a possible correlation between the presence of slowly rising gas rotation
curves and the ratio of the bulge/disc half-luminosity radii, while there is no obvious correlation with the key parameter
represented by the morphological classification, namely the bulge/disc luminosity ratio. Systems with a diffuse, dynamically
hot component (bulge or lens) with a scale length comparable to that of the disc are characterized by slowly rising gas rotation
curves. On the other hand, in systems with a small bulge the gas follows almost circular motions, regardless of the luminosity
of the bulge itself. We noticed a similar behaviour also in the gas and stellar kinematics of the two early-type spiral galaxies
modelled by Corsini et al.(1998).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
In a previous paper (hereafter referred to as Paper I) we have tried to show that superdense cores in the nuclei of disk galaxies can be formed by accretion of gas ejected by the evolved stars which populate the central bulge of these galaxies. Solving the equations for radial flow of a magnetized gas, we found that the accretion of an explodable mass at the core can be achieved over a time-scale ranging from a few times 107 and a few times 108 yr. It was shown, however, that the accretion process is seriously inhibited if the gas possesses sufficient rotational velocity but lacks any dissipative, mechanism within the system. Since rotational velocity is an observed parameter of the stars which shed the gas to be accreted, one must consider the existence of some dissipative force in it in order that the accretion process may be efficient. In the present paper, therefore, we have solved the problem of the flow of a rotating, viscous (variable), magnetized gas. With plausible assumptions regarding some of the parameters involved, the time-scale for the accretion of an explodable mass (109
M
) at the core again turns out to be ranging between a few times 107 and a few times 108yr. Such time-scale has been proposed by several authors as that for repeated explosions in nuclei of these galaxies. It has also been proposed by many authors that the spiral arms are generated and destroyed in disk galaxies over the same time-scale. Our solution also yields a nearly linear rotational velocity law which is usually observed in the central regions of these galaxies. 相似文献
16.
We use a semi-analytic model of halo formation to study the dynamical history of giant field galaxies like the Milky Way.
We find that in a concordance LCDM cosmology, most isolated disk galaxies have remained undisturbed for 8–10 Gyr, such that
the age of the Milky Way's thin disk is unremarkable. Many systems also have older disk components which have been thickened
by minor mergers, consistent with recent observations of nearby field galaxies. We do have a considerable problem, however,
reproducing the morphological mix of nearby galaxies. In our fiducial model, most systems have disk-to-bulge mass ratios of
order 1, and look like S0s rather than spirals. This result depends mainly on merger statistics, and is unchanged for most
reasonable choices of our model parameters. We discuss two possible solutions to this morphology problem in LCDM.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
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
18.
We present data for a sample of 45 spiral galaxies over a range of Hubble types, imaged in the near-IR J K bands. Parameters are calculated describing the bulge, disc and bar K -band light distributions, and we look for correlations showing the interrelation between these components. We find that bulge profiles are not well-fitted by the classic de Vaucouleurs profile, and that exponential or R 1/2 fits are preferred. The bulge-to-disc ratio correlates only weakly with Hubble type. Many of the galaxies show central reddening of their J − K colours, which we interpret as due to nuclear starbursts or dusty AGN. We define a new method for measuring the strength of bars, which we call 'equivalent angle'. We stress that this is better than the traditional bar–interbar contrast, as it is not subject to seeing and resolution effects. Bars are found in 40 of the 45 galaxies, nine of which had been previously classified as unbarred. Bar strengths are found not to correlate with disc surface brightness or the presence of near neighbours, but a tendency is found for the most strongly barred galaxies to lie within a restricted, intermediate range of bulge-to-disc ratio. Bar light profiles are found to be either flat or exponentially decreasing along their long axes, with profile type not correlating strongly with Hubble type. Bar short axis profiles are significantly asymmetric, with the steeper profile being generally on the leading edge, assuming trailing arms. In the K band we find bars with higher axial ratios than have been found previously in optical studies. 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.
Tao Hu Qiu-He Peng Hong-Shi Zong 《中国天文和天体物理学报》2007,7(4):579-589
We present disk thicknesses, some other parameters and their statistics of 108 non-edge-on spiral galaxies. The method for determining the disk thickness is based on solving Poisson's equation for a disturbance of matter density in three-dimensional spiral galaxies. From the spiral arms found we could obtain the pitch angles, the inclination of the galactic disk, and the position of the innermost point (the forbidden region with radius r 0 to the galactic center) of the spiral arm, and finally the thickness. 相似文献