Some properties of an intrinsically degenerate Hamiltonian system

Using theoretical arguments we study some properties of a time independent, two-dimensional Hamiltonian system in the 1:1 resonance case. In particular we find the frequency of the oscillation near the elliptic points, the ratio of the semiaxes of the ellipses surrounding them and the inclination angle of the asymptotes of the hyperbolic orbits in the original variablesx–p _x. The results are in satisfactory agreement with those given by numerical integration of the equations of motion. Some possible applications for the motion of stars in elliptical galaxies are also discussed.     

Central cusp caused by a supermassive black hole in axisymmetric models of elliptical galaxies

We use numerical simulations to investigate the cusp at the centre of elliptical galaxies caused by the slow growth of a supermassive black hole. We study this problem for axisymmetric models of galaxies with or without rotation. The numerical simulations are based on the 'perturbation particles' method, and use GRAPEs to compute the force arising from the cusp. We study the way in which the density cusp is affected by the initial flattening of the model, as well as the role played by initial rotation. The logarithmic slope of the density cusp is found to be very much insensitive to flattening; as a consequence, we deduce that tangential velocity anisotropy – which supports the flattening – is also of little influence on the final cusp. We investigate, via two different kinds of rotating models, the efficiency with which a rotation velocity component builds within the cusp. A cusp in rotation develops only for models where a net rotation component is initially present at high energy levels. The eventual observation of a central rotational velocity peak in elliptical galaxies has, therefore, some implications for the galaxy dynamical history.     

Searching for tidal tails – investigating galaxy harassment

Galaxy harassment has been proposed as a physical process that morphologically transforms low surface density disc galaxies into dwarf elliptical galaxies in clusters. It has been used to link the observed very different morphology of distant cluster galaxies (relatively more blue galaxies with 'disturbed' morphologies) with the relatively large numbers of dwarf elliptical galaxies found in nearby clusters. One prediction of the harassment model is that the remnant galaxies should lie on low surface brightness tidal streams or arcs. We demonstrate in this paper that we have an analysis method that is sensitive to the detection of arcs down to a surface brightness of 29 B μ and we then use this method to search for arcs around 46 Virgo cluster dwarf elliptical galaxies. We find no evidence for tidal streams or arcs and consequently no evidence for galaxy harassment as a viable explanation for the relatively large numbers of dwarf galaxies found in the Virgo cluster.     

Dynamical friction on globular clusters in core-triaxial galaxies: is it a cause of massive black hole accretion?

The present work extends and deepens previous examinations of the evolution of globular cluster orbits in elliptical galaxies, by means of numerical integrations of a wide set of orbits in five self-consistent triaxial galactic models characterized by a central core and different axial ratios. These models are valid and complete in the representation of regular orbits in elliptical galaxies. Dynamical friction is definitely shown to be an efficient cause of evolution for the globular cluster systems in elliptical galaxies of any mass or axial ratio. Moreover, our statistically significant sample of computed orbits confirms that the globular cluster orbital decay times are, at least for clusters moving on box orbits, much shorter than the age of the galaxies. Consequently, the mass carried into the innermost galactic region in the form of decayed globular clusters may have contributed significantly to feeding and accreting a compact object therein.     

Determining the character of motion in quiet and active galaxies with a satellite companion

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 massM_n. 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)     

Integrable models of galactic discs with double nuclei

We introduce a new class of 2D mass models, whose potentials are of Stäckel form in elliptic coordinates. Our model galaxies have two separate strong cusps that form double nuclei. The potential and surface density distributions are locally axisymmetric near the nuclei and become highly non-axisymmetric outside the nucleus. The surface density diverges toward the cuspy nuclei with the law     Our model is sustained by four general types of regular orbits: butterfly , nucleophilic banana , horseshoe and aligned loop orbits. Horseshoes and nucleophilic bananas support the existence of cuspy regions. Butterflies and aligned loops control the non-axisymmetric shape of outer regions. Without any need for central black holes, our distributed mass models resemble the nuclei of M31 and NGC 4486B. It is also shown that the self-gravity of the stellar disc can prevent the double nucleus to collapse.     

Dynamics of the boxy elliptical galaxy NGC 1600

We use three-integral models to infer the distribution function (DF) of the boxy E3–E4 galaxy NGC 1600 from surface brightness and line-profile data on the minor and major axes. We assume axisymmetry and that the mass-to-light ratio is constant in the central ∼1 R _e. Stars in the resulting gravitational potential move mainly on regular orbits. We use an approximate third integral K from perturbation theory and write the DF as a sum of basis functions in the three integrals E , L _z and K . We then fit the projected moments of these basis functions to the kinematic observables and deprojected density, using a non-parametric algorithm. The deduced dynamical structure is radially anisotropic, with σ _θ σ _r ≈ σ _φ σ _r ≈0.7 on the major axis. Both on the minor axis and near the centre the velocity distribution is more isotropic; thus the model is flattened by equatorial radial orbits. The kinematic data are fitted without the need for a central black hole; the central mass determined previously from ground-based data therefore overestimates the actual black-hole mass. The mass-to-light ratio of the stars is M L _V =6  h ₅₀. The anisotropy structure of NGC 1600 with a radially anisotropic main body and more nearly isotropic centre is similar to that found recently in NGC 1399, 2434, 3379 and 6703, suggesting that this pattern may be common amongst massive elliptical galaxies. We discuss a possible merger origin of NGC 1600 in the light of these results.     

How special are brightest group and cluster galaxies?

We use the Sloan Digital Sky Survey (SDSS) to construct a sample of 625 brightest group and cluster galaxies (BCGs) together with control samples of non-BCGs matched in stellar mass, redshift and colour. We investigate how the systematic properties of BCGs depend on stellar mass and on their privileged location near the cluster centre. The groups and clusters that we study are drawn from the C4 catalogue of Miller et al. but we have developed improved algorithms for identifying the BCG and for measuring the cluster velocity dispersion. Since the SDSS photometric pipeline tends to underestimate the luminosities of large galaxies in dense environments, we have developed a correction for this effect which can be readily applied to the published catalogue data. We find that BCGs are larger and have higher velocity dispersions than non-BCGs of the same stellar mass, which implies that BCGs contain a larger fraction of dark matter. In contrast to non-BCGs, the dynamical mass-to-light ratio of BCGs does not vary as a function of galaxy luminosity. Hence BCGs lie on a different Fundamental Plane than ordinary elliptical galaxies. BCGs also follow a steeper Faber–Jackson relation than non-BCGs, as suggested by models in which BCGs assemble via dissipationless mergers along preferentially radial orbits. We find tentative evidence that this steepening is stronger in more massive clusters. BCGs have similar mean stellar ages and metallicities to non-BCGs of the same mass, but they have somewhat higher α/Fe ratios, indicating that star formation may have occurred over a shorter time-scale in the BCGs. Finally, we find that BCGs are more likely to host radio-loud active galactic nuclei than other galaxies of the same mass, but are less likely to host an optical active galactic nucleus (AGN). The differences we find are more pronounced for the less massive BCGs, i.e. they are stronger at the galaxy group level.     

Nucleated dwarf elliptical galaxies in the Virgo cluster

Using images from a charge-coupled device survey with the Wide Field Camera on the Isaac Newton Telescope, we performed B - and I -band photometry on 156 Virgo cluster dwarf elliptical (dE) galaxies, 25 candidate new cluster dwarfs, and nine candidate field dwarfs. Galaxies were modelled with Sérsic profiles, using both 1D χ² and 2D cross-correlation methods, with nuclei modelled as point sources. The intensity profiles of 50 galaxies previously classified as dE, dE?, or ? are more accurately fitted if a nucleus is included, and this results in the majority of dwarfs now being classified as nucleated dwarf ellipticals (dE,N). Some faint galaxies with B magnitudes of 18–21 have particularly large relative nuclei, while a small number have apparent central dimmings. For cluster dE,N galaxies the nucleus magnitude is correlated with the magnitude of the host galaxy. The profile parameters of dE and dE,N galaxies are not significantly different, and there is no evident discontinuity in relative nucleus size between non-nucleated and nucleated dwarfs, suggesting that they may form a continuum. Nuclei are on average redder than their underlying galaxies, though a spread of relative colours was found, and two-fifths of nuclei are bluer. Formation mechanisms of nuclei are discussed: at least some appear to have formed in an already existing non-nucleated galaxy, though others may have formed simultaneously with their galaxies and subsequently evolved within them.     

The surface brightness and colour–magnitude relations for Fornax cluster galaxies

We present BVI photometry of 190 galaxies in the central 4 ×3 deg² region of the Fornax cluster observed with the Michigan Curtis Schmidt Telescope. Results from the Fornax Cluster Spectroscopic Survey (FCSS) and the Flair-II Fornax Surveys have been used to confirm the membership status of galaxies in the Fornax Cluster Catalogue (FCC). In our catalogue of 213 member galaxies, 92 (43 per cent) have confirmed radial velocities.
In this paper, we investigate the surface brightness–magnitude relation for Fornax cluster galaxies. Particular attention is given to the sample of cluster dwarfs and the newly discovered ultracompact dwarf galaxies (UCDs) from the FCSS. We examine the reliability of the surface brightness–magnitude relation as a method for determining cluster membership and find that at surface brightnesses fainter than 22 mag arcsec⁻², it fails in its ability to distinguish between cluster members and barely resolved background galaxies. Cluster members exhibit a strong surface brightness–magnitude relation. Both elliptical (E) galaxies and dwarf elliptical (dE) galaxies increase in surface brightness as luminosity decreases. The UCDs lie off the locus of the relation.
  B − V   and   V − I   colours are determined for a sample of 113 cluster galaxies and the colour–magnitude relation is explored for each morphological type. The UCDs lie off the locus of the colour–magnitude relation. Their mean   V − I   colours (∼1.09) are similar to those of globular clusters associated with NGC 1399. The location of the UCDs on both surface brightness and colour–magnitude plots supports the 'galaxy threshing' model for infalling nucleated dwarf elliptical (dE, N) galaxies.     

On the photometric redshift estimates for FR II radio galaxies

Using the photometric data on FR II radio galaxies obtained during the Big Trio program and data from other sources, we confirmed the stable correlation between the spectroscopic and photometric redshifts up to z ～ 4, determined from the evolutionary synthetic spectra of elliptical galaxies. This is confirmation of the theoretical predictions of the existence of a stellar population at high redshifts and its subsequent evolution corresponding to the population of giant elliptical galaxies.     

Motion of a Rigid Body in a Tidal Field

We investigate the motion, near the equilibrium configurations, of an initially spinless rigid body subject to an external tidal field. Two cases are considered: when the center of mass of the body is at rest at the equilibrium point of the field generated by a generic mass distribution, and when it is placed on a circular orbit subject to a spherically symmetric potential. A complete analysis of the equilibrium configurations is carried out for both cases. First, we derive the conditions for the stable equilibria, and then we analyze the frequencies of oscillations around the equilibrium positions. In view of these results, we consider the problem of alignment of galaxies in clusters. After estimating the period of the oscillations induced on the galaxies by the tidal field of the cluster, we discuss the possible effect of resonances between stellar orbits inside the galaxy and the oscillations of the galaxy as a whole; this may be a mechanism responsible for producing an intracluster stellar population. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparing peanut-shaped `bulges' to N-body simulations and orbital calculations

We present a near-infrared K _n-band photometric study of edge-on galaxies with a box/ peanut-shaped `bulge'. The morphology of the galaxies is analysed using unsharp masking and fits to the vertical surface brightness profiles, and the results are compared to N-body simulations and orbital calculations of barred galaxies. Both theoretical approaches reproduce the main structures observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Modelling of seeing effects in extragalactic astronomy and cosmology

Convolution methods for modelling of astronomical seeing effects have been investigated. The advantages and disadvantages of several techniques are discussed, and particular attention is given to the fast Fourier transform (FFT) method. This method is then applied to two classes of problems, the structure of cores of elliptical galaxies, appearance of distant galaxies and the consequences of seeing effects in some cosmological tests. Estimates are presented for dimming of the central surface brightness and changes in the apparent core radius for elliptical galaxies, as well as seeing-induced changes in ellipticity. Modelling of galaxies with stellar nuclei has also been performed. Some consequences of these effects in investigations of dynamics of elliptical galaxies are addressed briefly. The influence of seeing in observational cosmology is discussed in the context of Hubble diagram (m-z) tests. It is shown that inadequate compensation for seeing effects can seriously distort the conclusions in such tests. Some suggestions for future work in this direction are offered.     

Infrared–red cores in nearby elliptical galaxies

We present the Spitzer Space Telescope Infrared Array Camera observations for a sample of local elliptical galaxies to study later stages of active galactic nucleus (AGN) activity. A sample of 36 elliptical galaxies is selected from the Palomar spectroscopic survey. We detect nuclear non-stellar infrared emission in nine of them. There is unambiguous evidence of circumnuclear dust in these nine galaxies in their optical images. We also find a remarkable correlation between the infrared excess emission and the nuclear radio/X-ray emission, suggesting that infrared excess emission is tightly related to nuclear activity. The possible origin of infrared excess emission from hot dust heated by the central AGN is supported by the spectral indices of the infrared excess emission.     

The cataclysmic variable period gap: still there

We have measured central line strengths for a complete sample of early-type galaxies in the Fornax cluster, comprising 11 elliptical and 11 lenticular galaxies, more luminous than M _B  = −17. In contrast to the elliptical galaxies in the sample studied by González (and recently revisited by Trager) we find that the Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models and have metallicities varying from roughly solar to three times solar. The lenticular galaxies, however, exhibit a substantial spread to younger luminosity-weighted ages, indicating a more extended star formation history. We present measurements of the more sensitive indices: C4668 and Hγ_A; these confirm and reinforce the conclusions that the elliptical galaxies are coeval and that only the lenticular galaxies show symptoms of late star formation. The inferred difference in the age distribution between lenticular and elliptical galaxies is a robust conclusion as the models generate consistent relative ages using different age and metallicity indicators even though the absolute ages remain uncertain. The young luminosity-weighted ages of the S0s in the Fornax cluster are consistent with the recent discovery that the fraction of S0 galaxies in intermediate-redshift clusters is a factor of 2–3 lower than found locally, and suggest that a fraction of the cluster spiral galaxy population has evolved to quiescence in the 5-Gyr interval from z  = 0.5 to the present. Two of the faintest lenticular galaxies in our sample have blue continua and strong Balmer-line absorption, suggesting starbursts ≲2 Gyr ago. These may be the low-redshift analogues of the starburst or post-starburst galaxies seen in clusters at z  = 0.3, similar to the Hδ-strong galaxies in the Coma cluster.     

On the detectability of turbulence and bulk flows in X-ray clusters

Coolingflows, cluster mergers, and the motions of galaxies through cluster gas with supersonic and sonic velocities must lead to large scale motions of the intracluster medium (ICM). A high-resolution numerical simulation of X-ray cluster formation by Norman and Bryan (1999) predicts cluster-wide turbulence with ν_turb ≈300–600 km s^?1 and eddy scales l_outer ≈100–500 kpc, the larger numbers being characteristic of turbulence near the virial radius, while the smaller numbers pertain to the core. The simulation also predicts the existence of ordered bulk flows in the core with v≈400 km s^?1 on scales of several hundred kpc. In this paper, we consider the observability of such fluid motions via the distortions they induce in the CMB via the kinematic SZ effect, as well as via Doppler broadening and shifting of metal lines in the X-ray spectrum. We estimate |ΔT/T|_kinematic?6—at or below current limits of detectability. However, we find that an energy resolution of a few eV is sufficient to detect several Doppler shifted components in the 6.7 keV Fe line in the cluster core.     

Boxy/peanut 'bulges': comparing the structure of galaxies with the underlying families of periodic orbits

The vertical profiles of disc galaxies are built by the material trapped around stable periodic orbits, which form their 'skeletons'. Therefore, knowledge of the stability of the main families of periodic orbits in appropriate 3D models enables one to predict possible morphologies for edge-on disc galaxies. In a pilot survey we compare the orbital structures that lead to the appearance of 'peanut'- and 'X'-like features with the edge-on profiles of three disc galaxies (IC 2531, NGC 4013 and UGC 2048). The subtraction from the images of a model representing the axisymmetric component of the galaxies reveals the contribution of the non-axisymmetric terms. We find a direct correspondence between the orbital profiles of 3D bars in models and the observed main morphological features of the residuals. We also apply a simple unsharp masking technique in order to study the sharpest features of the images. Our basic conclusion is that the morphology of the boxy 'bulges' of these galaxies can be explained by considering disc material trapped around stable 3D periodic orbits. In most models, these building-block periodic orbits are bifurcated from the planar central family of a non-axisymmetric component, usually a bar, at low-order vertical resonances. In such a case, the boxy 'bulges' are parts of bars seen edge-on. For the three galaxies we study, the families associated with the 'peanut' or 'X'-shape morphology are probably bifurcations at the vertical 2/1 or 4/1 resonance.     

Gas dynamic stripping and X-ray emission of cluster elliptical galaxies

Detailed three-dimensional numerical simulations of an elliptical galaxy orbiting in a gas-rich cluster of galaxies indicate that gas dynamic stripping is less efficient than the results from previous, simpler calculations by Takeda et al. and Gaetz et al. implied. This result is consistent with X-ray data for cluster elliptical galaxies. Hydrodynamic torques and direct accretion of orbital angular momentum can result in the formation of a cold gaseous disc, even in a non-rotating galaxy. The gas lost by cluster galaxies via the process of gas dynamic stripping tends to produce a colder, chemically enriched cluster gas core. A comparison of the models with the available X-ray data of cluster galaxies shows that the X-ray luminosity distribution of cluster galaxies may reflect hydrodynamic stripping, but also that a purely hydrodynamic treatment is inadequate for the cooler interstellar medium near the centre of the galaxy.     

Massive dark matter haloes around bright isolated galaxies in the 2dFGRS

We identify a large sample of isolated bright galaxies and their fainter satellites in the 2dF Galaxy Redshift Survey (2dFGRS). We analyse the dynamics of ensembles of these galaxies selected according to luminosity and morphological type by stacking the positions of their satellites and estimating the velocity dispersion of the combined set. We test our methodology using realistic mock catalogues constructed from cosmological simulations. The method returns an unbiased estimate of the velocity dispersion provided that the isolation criterion is strict enough to avoid contamination and that the scatter in halo mass at fixed primary luminosity is small. Using a maximum likelihood estimator that accounts for interlopers, we determine the satellite velocity dispersion within a projected radius of 175  h ⁻¹ kpc. The dispersion increases with the luminosity of the primary and is larger for elliptical galaxies than for spiral galaxies of similar b _J luminosity. Calibrating the mass–velocity dispersion relation using our mock catalogues, we find a dynamical mass within 175  h ⁻¹ kpc of     for elliptical galaxies and     for spiral galaxies. Finally, we compare our results with recent studies and investigate their limitations using our mock catalogues.