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1.
We study the nature of the extended near-UV emission in the inner kiloparsec of a sample of 15 Seyfert (Sy) galaxies which have both near-UV (F330W) and narrow-band [O  iii ] high-resolution Hubble images. For the majority of the objects, we find a very similar morphology in both bands. From the [O  iii ] images, we construct synthetic images of the nebular continuum plus the emission-line contribution expected through the F330W filter, which can be subtracted from the F330W images. We find that the emission of the ionized gas dominates the near-UV extended emission in half of the objects. A further broad-band photometric study, in the bands F330W ( U ), F547M ( V ) and F160W ( H ), shows that the remaining emission is dominated by the underlying galactic bulge contribution. We also find a blue component whose nature is not clear in four out of 15 objects. This component may be attributed to scattered light from the active galactic nuclei, to a young stellar population in unresolved star clusters, or to early disrupted clusters. Star-forming regions and/or bright off nuclear star clusters are observed in 4/15 galaxies of the sample.  相似文献   

2.
Globular clusters rotate significantly, and with the increasing amount of detailed morphological and kinematical data obtained in recent years on galactic globular clusters many interesting features show up. We show how our theoretical evolutionary models of rotating clusters can be used to obtain fits, which at least properly model the overall rotation and its implied kinematics in full 2D detail (dispersions, rotation velocities). Our simplified equal mass axisymmetric rotating model provides detailed two-dimensional kinematical and morphological data for star clusters. The degree of rotation is not dominant in energy, but also non-negligible for the phase-space distribution function, shape and kinematics of clusters. Therefore, the models are well applicable for galactic globular clusters. Since previously published papers on that matter by us made it difficult to do detailed comparisons with observations, we provide a much more comprehensive and easy-to-use set of data here, which uses as entries dynamical age and flattening of observed cluster and then offers a limited range of applicable models in full detail. The method, data structure and some exemplary comparison with observations are presented. Future work will improve modelling and data base to take a central black hole, a mass spectrum and stellar evolution into account.  相似文献   

3.
Recent X-ray observations have shown that intracluster medium has non-primordial composition. Iron lines have been detected. We present preliminary results on modelling of the chemical evolution of the intracluster medium in galaxy clusters. We consider in detail the galactic winds driven by supernovae, taking into account the binding energy of the galactic gas. We try to explain the metallicity gradient observed in the Perseus cluster from morphological segregation of galaxies in the inner part of the cluster.  相似文献   

4.
A model is presented for the chemical evolution of the solar neighbourhood which takes into account three families of galactic objects, according to their condensation states: stars, refuses and gas. Stars are defined as all condensed objects with masses greater than or equal to the minimum mass which ignites hydrogen and which will give rise to an evolutionary track on the HR diagram to the left of Hayashi's limit; refuses include the remnants, which are compact objects resulting from stellar deaths, and the residues, which have masses not large enough to ignite hydrogen; gas is defined as the mass which can be condensed to form stars and/or residues. We have developed equations for the mass evolution of each family, and have studied the gas metallicity distribution within the framework of the instantaneous recycling approximation, adopting different initial conditions. In order to constrain the model parameters we have also used preliminary evaluations of comet cloud masses to investigate the role of the residues as sinks of heavy elements in the Galaxy.  相似文献   

5.
The new approach outlined in Paper I to follow the individual formation and evolution of binaries in an evolving, equal point-mass star cluster is extended for the self-consistent treatment of relaxation and close three- and four-body encounters for many binaries (typically a few per cent of the initial number of stars in the cluster mass). The distribution of single stars is treated as a conducting gas sphere with a standard anisotropic gaseous model. A Monte Carlo technique is used to model the motion of binaries, their formation and subsequent hardening by close encounters, and their relaxation (dynamical friction) with single stars and other binaries. The results are a further approach towards a realistic model of globular clusters with primordial binaries without using special hardware. We present, as our main result, the self-consistent evolution of a cluster consisting of 300 000 equal point-mass stars, plus 30 000 equal-mass binaries over several hundred half-mass relaxation times, well into the phase where most of the binaries have been dissolved and evacuated from the core. The cluster evolution is about three times slower than found by Gao et al. Other features are rather comparable. At every moment we are able to show the individual distribution of binaries in the cluster.  相似文献   

6.
It has been suggested by several authors that the infra-red emission from galactic nuclei is due to synchrotron process from compact objects or due to thermal processes. We have examined here the coherent and incoherent synchrotron mechanisms from compact objects and find that these are unlikely to explain the observed emission.  相似文献   

7.
Periodic explosions in the nucleus of a galaxy generate strong shock waves. The shock waves, in moving outwards, produce highly compressed thin layers of gas at distances much larger than the thickness of the layer. When the gas in this layer undergoes fragmentation, the Jeans mass is found to be much less than that if the fragmentation proceeded under normal gravitational pull. It is, therefore, concluded that the explosive events in the galactic centres make the process of star formation highly efficient in the central region of galaxies.  相似文献   

8.
We present gas temperature, density, entropy and cooling time profiles for the cores of a sample of 15 galaxy groups observed with Chandra . We find that the entropy profiles follow a power-law profile down to very small fractions of R 500. Differences between the gas profiles of groups with radio-loud and radio-quiet brightest group galaxies are only marginally significant, and there is only a small difference in the   L X: T X  relations, for the central regions we study with Chandra , between the radio-loud and radio-quiet objects in our sample, in contrast to the much larger difference found on scales of the whole group in earlier work. However, there is evidence, from splitting the sample based on the mass of the central black holes, that repeated outbursts of active galactic nuclei (AGN) activity may have a long-term cumulative effect on the entropy profiles. We argue that, to first order, energy injection from radio sources does not change the global structure of the gas in the cores of groups, although it can displace gas on a local level. In most systems, it appears that AGN energy injection serves primarily to counter the effects of radiative cooling, rather than being responsible for the similarity breaking between groups and clusters.  相似文献   

9.
We describe the results of our spectroscopy for a sample of barred galaxies whose inner regions exhibit an isophotal twist commonly interpreted as a secondary bar. The line-of-sight velocity fields of the ionized gas and stars and the light-of-sight velocity dispersion fields of the stars were constructed from two-dimensional spectroscopy with the 6-m Special Astrophysical Observatory telescope. We detected various types of noncircular motions of ionized gas: radial flows within large-scale bars, counterrotation of the gas and stars at the center of NGC 3945, a polar gaseous disk in NGC 5850, etc. Our analysis of the optical and near-infrared galaxy images (both ground-based and those from the Hubble Space Telescope) revealed circumnuclear minispirals in five objects. The presence of an inner (secondary) bar in the galaxy images is shown to have no effect on the circumnuclear kinematics of the gas and stars. Thus, contrary to popular belief, the secondary bar is not a dynamically decoupled galactic structure. We conclude that the so-called double-barred galaxies are not a separate type of galaxy but are a combination of objects with distinctly different morphologies of their circumnuclear regions.  相似文献   

10.
Spherically symmetric stellar clusters (compact galactic nuclei and globular clusters), far advanced toward the state of complete statistical equilibrium in the course of evolution, are investigated. The equation of state of such systems (a polytrope with an index k = 0.5) is derived and their main characteristics are calculated. It is shown that compact galactic nuclei must consist mainly of rapidly rotating neutron stars and white dwarfs. It is demonstrated that pulsars may be created by the evaporation of neutron stars from the nucleus of our Galaxy. The number of such pulsars is ~3.106. Translated from Astrofizika, Vol. 41, No. 1, pp. 41–50, January-March, 1998.  相似文献   

11.
We have recently shown that X-ray observations of the population of 'low-excitation' radio galaxies, which includes most low-power, Fanaroff–Riley class I sources as well as some more powerful Fanaroff–Riley class II objects, are consistent with a model in which the active nuclei of these objects are not radiatively efficient at any waveband. In another recent paper, Allen et al. have shown that Bondi accretion of the hot, X-ray emitting phase of the intergalactic medium (IGM) is sufficient to power the jets of several nearby, low-power radio galaxies at the centres of clusters. In this paper, we combine these ideas and suggest that accretion of the hot phase of the IGM is sufficient to power all low-excitation radio sources, while high-excitation sources are powered by accretion of cold gas that is in general unrelated to the hot IGM. This model explains a number of properties of the radio-loud active galaxy population, and has important implications for the energy input of radio-loud active galactic nuclei into the hot phase of the IGM: the energy supply of powerful high-excitation sources does not have a direct connection to the hot phase.  相似文献   

12.
We have examined the effects of the ultraviolet background radiation (UVB) on the colour–magnitude relation (CMR) of elliptical galaxies in clusters of galaxies in the hierarchical clustering scenario by using a semi-analytic model of galaxy formation. In our model the UVB photoionizes gas in dark haloes and suppresses the cooling of the diffuse hot gas on to galaxy discs. By using a semi-analytic model without the effect of the UVB, Kauffmann & Charlot found that the CMR can be reproduced by strong supernova heating because such supernova feedback suppresses the chemical enrichment in galaxies, especially for small galaxies. We find that the CMR also becomes bluer because of the UVB, in a different way from the effect of supernova feedback. While supernova feedback suppresses the chemical enrichment by a similar mechanism to galactic winds, the UVB suppresses the cooling of the hot gas. This induces suppression of the metallicity of the intracluster medium (ICM). In our model we find that the existence of the UVB can plausibly account for an observed ICM metallicity that is equal to nearly 0.3 times the solar value, and that in this case we can reproduce the CMR and the metallicity of the ICM simultaneously.  相似文献   

13.
We have been undertaking a programme on the Gemini 8‐m telescopes to demonstrate the power of integral field spectroscopy, using the optical GMOS spectrograph, and the new CIRPASS instrument in the near‐infrared. Here we present some preliminary results from 3D spectroscopy of extra‐galactic objects, mapping the emission lines in a 3CR radio galaxy and in a gravitationally lensed arc, exploring dark matter sub‐structure through observations of an Einstein Cross gravitational lens, and the star formation time‐scales of young massive clusters in the starburst galaxy NGC 1140. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
We investigate the history of galactic feedback and chemical enrichment within a sample of 15 X-ray bright groups of galaxies, on the basis of the inferred Fe and Si distributions in the hot gas and the associated metal masses produced by core-collapse and Type Ia supernovae (SNe). Most of these cool-core groups show a central Fe and Si excess, which can be explained by prolonged enrichment by SN Ia and stellar winds in the central early-type galaxy alone, but with tentative evidence for additional processes contributing to core enrichment in hotter groups. Inferred metal mass-to-light ratios inside r 500 show a positive correlation with total group mass but are generally significantly lower than in clusters, due to a combination of lower global intracluster medium (ICM) abundances and gas-to-light ratios in groups. This metal deficiency is present for products from both SN Ia and SN II, and suggests that metals were either synthesized, released from galaxies or retained within the ICM less efficiently in lower mass systems. We explore possible causes, including variations in galaxy formation and metal release efficiency, cooling out of metals, and gas and metal loss via active galactic nuclei (AGN) – or starburst-driven galactic winds from groups or their precursor filaments. Loss of enriched material from filaments coupled with post-collapse AGN feedback emerges as viable explanations, but we also find evidence for metals to have been released less efficiently from galaxies in cooler groups and for the ICM in these to appear chemically less evolved, possibly reflecting more extended star formation histories in less massive systems. Some implications for the hierarchical growth of clusters from groups are briefly discussed.  相似文献   

15.
We describe Monte Carlo models for the dynamical evolution of the nearby globular cluster NGC 6397. The code includes treatments of two-body relaxation, most kinds of three- and four-body interactions involving primordial binaries and those formed dynamically, the Galactic tide and the internal evolution of both single and binary stars. We arrive at a set of initial parameters for the cluster which, after 12 Gyr of evolution, gives a model with a fairly satisfactory match to the surface brightness profile, the velocity dispersion profile and the luminosity function in two fields. We describe in particular those aspects of the evolution which distinguish this cluster from M4, which has a roughly similar mass and Galactocentric distance, but a qualitatively different surface brightness profile. Within the limitations of our modelling, we conclude that the most plausible explanation for the difference is fluctuations: both clusters are post-collapse objects, but sometimes have resolvable cores and sometimes not.  相似文献   

16.
The transformation of the energy of an accelerating, expanding universe into internal energy of cosmic objects is discussed. The well known fact that Hubble expansion is observed on scale lengths two or more orders of magnitude smaller than the “cells of homogeneity” is taken into account, along with observational data indicating that this expansion also takes place on the scale of the solar system. Changes in the potential energy of individual model objects are examined on this basis and it is shown that the potential energy increases, thereby threatening the continued existence of these objects. An expression is obtained for the mass which can attain the escape energy within a given energy accumulation time. Some estimates are made for the assumed masses of galactic clusters. Over a period of 107 years a protocluster can accumulate enough energy for ejection of a clump of matter with a mass equal to that of our galaxy.  相似文献   

17.
We propose a model of chemical evolution of the galactic halo which consists of a succession of two different evolutionary stages; each stage is characterized by different outflow rate of gas from the star-forming region so that different metal-enrichment rate is resulted. The low-metal stars with [Fe/H]<–0.8 are formed mainly during the first 3×108 yr, and most of the high-metal stars with [Fe/H]–0.8 are formed during the succeeding 2×109 yr. This model naturally explains the metallicity distribution of globular clusters in the galactic halo including both the metal-rich and the metal-poor clusters. We also discuss the implications of the present model on the formation and evolution of the galactic halo.  相似文献   

18.
Starforming factories in galaxies produce compact clusters and loose associations of young massive stars. Fast radiation-driven winds and supernovae input their huge kinetic power into the interstellar medium in the form of highly supersonic and superalfvenic outflows. Apart from gas heating, collisionless relaxation of fast plasma outflows results in fluctuating magnetic fields and energetic particles. The energetic particles comprise a long-lived component which may contain a sizeable fraction of the kinetic energy released by the winds and supernova ejecta and thus modify the magnetohydrodynamic flows in the systems. We present a concise review of observational data and models of nonthermal emission from starburst galaxies, superbubbles, and compact clusters of massive stars. Efficient mechanisms of particle acceleration and amplification of fluctuating magnetic fields with a wide dynamical range in starburst regions are discussed. Sources of cosmic rays, neutrinos and multi-wavelength nonthermal emission associated with starburst regions including potential galactic “PeVatrons” are reviewed in the global galactic ecology context.  相似文献   

19.
Using three-dimensional (3D) magnetohydrodynamical (MHD) nested-grid simulations, the fragmentation of a rotating magnetized molecular cloud core is studied. An isothermal rotating magnetized cylindrical cloud in hydrostatic balance is considered. We studied non-axisymmetric evolution of the cloud. It is found that non-axisymmetry hardly evolves in the early phase, but it begins to grow after the gas contracts and forms a thin disk. The disk formation and thus growth of non-axisymmetric perturbation are strongly promoted by rotation and magnetic field strength. We found two types of fragmentations: fragmentation from a ring and that from a bar. These two types of fragmentations occur in thin adiabatic cores with the thickness being smaller than 1/4 of the radial size. For the fragments to survive, they should be formed in a heavily elongated barred core or a flat round disk. In the models showing fragmentation, outflows from respective fragments are found as well as that driven by the rotating bar or the disk.  相似文献   

20.
The differences between optical and X-ray structures of galaxy clusters are discussed. We analyse in detail 7 Abell clusters. There is an increasing number of arguments in favour of different distributions of galaxies, gas, and dark matter in many clusters. We argue that most clusters present sub-structures at least in the gaseous and galactic components and, moreover, the subclustering of different components does not always coincide. Such arguments strongly support the idea that most galaxy clusters are by far more complex systems than accepted until now and are usually not in an hydrostatic isothermal equilibrium.  相似文献   

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