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The travel time required for one civilisation to explore the Milky Way using probes is a crucial component of Fermi's Paradox. Previous attempts to estimate this travel time have assumed that the probe's motion is simple, moving at a constant maximum velocity, with powered flight producing the necessary change in velocity required at each star to complete its chosen trajectory. This approach ignores lessons learned from interplanetary exploration, where orbital slingshot maneouvres can provide significant velocity boosts at little to no fuel cost. It is plausible that any attempt to explore the Galaxy would utilise such economising techniques, despite there being an upper limit to these velocity boosts, related to the escape velocity of the object being used to provide the slingshot. In order to investigate the effects of these techniques, we present multiple realisations of single probes exploring a small patch of the Milky Way. We investigate 3 separate scenarios, studying the slingshot effect on trajectories defined by simple heuristics. These scenarios are: i) standard powered flight to the nearest unvisited star without using slingshot techniques; ii) flight to the nearest unvisited star using slingshot techniques, and iii) flight to the next unvisited star which provides the maximal velocity boost under a slingshot trajectory. We find that adding slingshot velocity boosts can decrease the travel time by up to two orders of magnitude over simple powered flight. In the third case, selecting a route which maximises velocity boosts also reduces the travel time relative to powered flight, but by a much reduced factor. From these simulations, we suggest that adding realistic probe trajectories tends to strengthen Fermi's Paradox.

This paper contains all known errata in the book "Galactic Dynamics".

It has been recently shown (Munyaneza, Tsiklauri and Viollier 1998) that the analysis of the orbits of the fast moving stars close to Sgr A$^{*}$ (Eckart and Genzel 1997) provides a valuable tool to probe the gravitational potential near the Galactic center. As an example, we present here the results on a calculation of possible orbits of the star S0-1 in both, the black hole and degenerate neutrino ball scenarios of the central mass, based on the recent measurements of stellar proper motions at the Galactic center by Ghez et al. 1998. Taking into account the error bars of their analysis, it is shown that within a few years time, the orbit of S0-1 may indeed reveal the nature of the supermassive compact dark object at the Galactic center.

We present Superbox, a particle-mesh code with high resolution sub-grids and an NGP (nearest grid point) force-calculation scheme based on the second derivatives of the potential. Superbox implements a fast low-storage FFT-algorithm, giving the possibility to work with millions of particles on desk-top computers. Test calculations show energy and angular momentum conservation to one part in 10^5 per crossing-time. The effects of grid and numerical relaxation remain negligible, even when these calculations cover a Hubble-time of evolution. As the sub-grids follow the trajectories of individual galaxies, the code allows a highly resolved treatment of interactions in clusters of galaxies, such as high-velocity encounters between elliptical galaxies and the tidal disruption of dwarf galaxies. Excellent agreement is obtained in a comparison with a direct-summation N-body code running on special-purpose Grape3 hardware. The orbital decay of satellite galaxies due to dynamical friction obtained with Superbox agrees with Chandrasekhar's treatment when the Coulomb logarithm is approximately 1.5.

The structure, kinematics and dynamics of the Galactic stellar halo are reviewed including evidence of substructure in the spatial distribution and kinematics of halo stars. Implications for galaxy formation theory are subsequently discussed; in particular it is argued that the observed kinematics of stars in the outer Galactic halo can be used as an important constraint on viable galaxy formation scenarios.

Certain steady states of the Vlasov-Poisson system can be characterized as minimizers of an energy-Casimir functional, and this fact implies a nonlinear stability property of such steady states. In previous investigations by Y. Guo and the author stability was obtained only with respect to spherically symmetric perturbations. In the present investigation we show how to remove this unphysical restriction.

We report a new analysis of stellar dynamics in the Galactic centre, based on improved sky and LOS velocities for >100 stars within a few arcsec of SgrA*. Overall the motions do not deviate strongly from isotropy. For 32 stars with all 3 components determined the absolute, LOS and sky velocities agree well, as for a spherical cluster. The projected radial and tangential motions of all 104 pm stars are also consistent with overall isotropy. However, the projected velocities of the young, early type stars have a strong radial dependence. Most of the bright HeI stars 1-10" from SgrA* are on tangential orbits. This anisotropy of the HeI stars and most of the brighter IRS16 complex members is largely caused by a CW and counter-rotating, coherent rotation pattern. The overall rotation of the young star cluster probably is a remnant of the angular momentum in the cloud these stars formed from. The fainter, fast stars within \~1" of SgrA* appear to be largely moving on radial or very elliptical orbits. We have not detected nonlinear motion for any of them. Most of the SgrA* cluster members also are on CW orbits. Spectroscopy shows them to be early type stars. We propose that the SgrA* cluster stars are those members of the early type cluster with small angular momentum which can plunge to the vicinity of SgrA*. Our anisotropy-independent estimate of the Sun-GC distance is 7.8-8.2 kpc (+/- 0.9 kpc). We include velocity anisotropy in estimating the central mass distribution. We confirm previous conclusions that a compact central mass concentration is present and dominates the potential from 0.01-1 pc. The central mass ranges from 2.6-3.3E6 M_sun. (abridged)

Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies.

Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies.

We follow the sinking of two massive black holes in a spherical stellar system where the black holes become bound under the influence of dynamical friction. Once bound, the binary hardens by three-body encounters with surrounding stars. We find that the binary wanders inside the core, providing an enhanced supply of reaction partners for the hardening. The binary evolves into a highly eccentric orbit leading to coalescence well beyond a Hubble time. These are the first results from a hybrid ``self consistent field'' (SCF) and direct Aarseth N-body integrator (NBODY6), which combines the advantages of the direct force calculation with the efficiency of the field method. The code is designed for use on parallel architectures and is therefore applicable to collisional N-body integrations with extraordinarily large particle numbers (> 10^5). This creates the possibility of simulating the dynamics of both globular clusters with realistic collisional relaxation and stellar systems surrounding supermassive black holes in galactic nuclei.

Using Dynamic Evolution or Emergent Behavior over billions of years to show the observed Galaxy Disks are natural without Dark Matter needed.

We present 0.2" resolution near-infrared integral field spectroscopy of H-alpha emission from six star forming galaxies at z~1.6 (look-back time of ~9.6 Gyr). These observations were obtained with OSIRIS using the Keck Laser Guide Star Adaptive Optics system. All sources have a compact spatial extent of ~1", with an average half light radius of r=2.9 kpc and average dereddened star formation rate of 22 Msolar per year. Based on H-alpha kinematics we find that these six galaxies are dynamically distinguishable, and we classify them as either merger or disk candidate systems. We find three merger systems (HDF-BX1287, HDF-BX1315, and Q1623-BX491) with varying geometries and dynamical properties. Three galaxies (HDF-BMZ1299, Q2343-BX344, and Q2343-BM145) are well-fit by an inclined-disk model with low velocity residuals (20 to 46 km/sec). An average plateau velocity of v_p=185 km/sec is achieved within 1.0 kpc. The majority of observed velocity dispersions (~88 km/sec) can be explained by the residual seeing halo, and are not intrinsic to our sources. However, one merger and one disk candidate have high velocity dispersions (> 200 km/sec) that cannot be solely explained by beam smearing. For two disk candidates, we detect [NII] emission and are able to map the [NII]/H-alpha ratio on kiloparsec scales. In both cases, [NII] emission is more concentrated than H-alpha emission ( < 0.2"), and peak ratios are best explained by the presence of an AGN. These are among the weakest known AGN at high redshift, however their emission is strong enough to impact high redshift metallicity studies that use nebular ratios. All disk candidates have likely completed only a few orbital periods, and if left unperturbed are excellent candidates to become present-day spiral galaxies.

Gaskell et al. (2007) introduced polarization reverberation mapping as a new technique to explore the structure of active galactic nuclei. We present modeling results for the time-dependent polarization signal expected from scattering inside a centrally illuminated spheroid. Such a model setup describes a larger corona surrounding the compact source of an active nucleus. Time-delays between the polarized and the total flux are computed and related to the geometry of the cloud and the viewing angle. When including the in-flow dynamics of the cloud, it is possible to constrain its optical depth and velocity, which enables estimations of the mass inflow rate.

We propose a unified framework that reconciles the stunning success of MOND on galactic scales with the triumph of the LambdaCDM model on cosmological scales. This is achieved through the physics of superfluidity. Dark matter consists of self-interacting axion-like particles that thermalize and condense to form a superfluid in galaxies, with ~mK critical temperature. The superfluid phonons mediate a MOND acceleration on baryonic matter. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures.

Action-angle coordinates are an essential tool for understanding the properties of the six dimensional phase space involved in orbits of stars in galactic potentials. A new method, which does not require specific knowledge of a generating function, is described, implemented and tested that calculates the actions of an orbit in an arbitrary potential of an integrable Hamiltonian given a set of Cartesian phase space points. The method chooses between the simple harmonic oscillator and isochrone potentials to fit the data using a Levenberg-Marquardt routine. An average is taken over the angle coordinates by calculating volumes in phase space using the metric free FiEstAS algorithm. The perfect ellipsoidal potential, with actions chosen a priori, is used to test the output of the algorithm, giving some results that agree within 1%. Minimisation of a sampling error is discussed along with an identification of a source of noise in the data.

The Galactic center hosts several hundred early-type stars, about 20% of which lie in the so-called clockwise disk, while the remaining 80% do not belong to any disks. The circumnuclear ring (CNR), a ring of molecular gas that orbits the supermassive black hole (SMBH) with a radius of 1.5 pc, has been claimed to induce precession and Kozai-Lidov oscillations onto the orbits of stars in the innermost parsec. We investigate the perturbations exerted by a gas ring on a nearly-Keplerian stellar disk orbiting a SMBH by means of combined direct N-body and smoothed particle hydrodynamics simulations. We simulate the formation of gas rings through the infall and disruption of a molecular gas cloud, adopting different inclinations between the infalling gas cloud and the stellar disk. We find that a CNR-like ring is not efficient in affecting the stellar disk on a timescale of 3 Myr. In contrast, a gas ring in the innermost 0.5 pc induces precession of the longitude of the ascending node Omega, significantly affecting the stellar disk inclination. Furthermore, the combined effect of two-body relaxation and Omega-precession drives the stellar disk dismembering, displacing the stars from the disk. The impact of precession on the star orbits is stronger when the stellar disk and the inner gas ring are nearly coplanar. We speculate that the warm gas in the inner cavity might have played a major role in the evolution of the clockwise disk.

We discuss experiments achievable via monitoring of stellar dynamics near the massive black hole at the Galactic center with a next generation, extremely large telescope (ELT). Given the likely observational capabilities of an ELT and current knowledge of the stellar environment at the Galactic center, we synthesize plausible samples of stellar orbits around the black hole. We use the Markov Chain Monte Carlo method to evaluate the constraints that orbital monitoring places on the matter content near the black hole. Results are expressed as functions of the number N of stars with detectable orbital motions and the astrometric precision dtheta and spectroscopic precision dv at which stellar proper motions and radial velocities are monitored. For N = 100, dtheta = 0.5 mas, and dv = 10 km/s -- a conservative estimate of the capabilities of a 30 meter telescope -- the extended matter distribution enclosed by the orbits will produce measurable deviations from Keplerian motion if >1000 Msun is enclosed within 0.01 pc. The black hole mass and distance to the Galactic center will be measured to better than ~0.1%. Lowest-order relativistic effects, such as the prograde precession, will be detectable if dtheta < 0.5 mas. Higher-order effects, including frame dragging due to black hole spin, requires dtheta < 0.05 mas, or the favorable discovery of a compact, highly eccentric orbit. Finally, we calculate the rate at which monitored stars undergo detectable nearby encounters with background stars. Such encounters probe the mass function of stellar remnants that accumulate near the black hole. We find that ~30 encounters will be detected over a 10 yr baseline for dtheta = 0.5 mas.

Modified Newtonian Dynamics (MOND) and its relativistic version - TeVeS offer us an alternative perspective to understand the universe without the demand of the elusive cold dark matter. This MONDian paradigm is not only competitive with the conventional CDM in a large range of scales, but also even more successful in the galactic scale. Recently, by studying 6 lensing systems, Ferreras et al. (2008) claimed that MOND still needs dark matter even in galactic scales. When we study the same systems, however, we yield an opposite conclusion. In this contribution, we report our result and conclude that MOND does not need dark matter in galactic lensing systems. Furthermore, we extend our study to 22 SLACS (Sloan Lens ACS Survey) lenses, and obtain the same conclusion as well, i.e., no dark matter is needed in elliptical galaxies.

The disruption of a star by the tidal field of a massive black hole is the final outcome of a chain of complex dynamical processes in the host galaxy. I introduce the "loss cone problem", and describe the many theoretical and numerical challenges on the path of solving it. I review various dynamical channels by which stars can be supplied to a massive black hole, and the relevant dynamical relaxation / randomization mechanisms. I briefly mention some "exotic" tidal disruption scenarios, and conclude by discussing some new dynamical results that are changing our understanding of dynamics near a massive black hole, and may well be relevant for tidal disruption dynamics.

We produce synthetic populations of pulsars within our Galaxy and calculate the resulting scale heights as well as the radial and space velocity distributions of the pulsars. Results are presented for isolated pulsars, binary pulsars and millisecond pulsars. We also test the robustness of the outcomes to variations in the assumed form of the Galactic potential, the birth distribution of binary positions, and the strength of the velocity kick given to neutron stars at birth. We find that isolated pulsars have a greater scale height than binary pulsars. This is also true when restricted to millisecond pulsars unless we allow for low-mass stars to be ablated by radiation from their pulsar companion in which case the isolated and binary scale heights are comparable. Double neutron stars are found to have a large variety of space velocities, in particular, some systems have speeds similar to the Sun. We look in detail at the predicted Galactic population of millisecond pulsars with black hole companions, including their formation pathways, and show where the short-period systems reside in the Galaxy. Some of our population predictions are compared in a limited way to observations but the full potential of this aspect will be realised in the near future when we complete our population synthesis code with the selection effects component.

The first N-body simulation of interacting galaxies, even producing spiral arms, was performed by Erik Holmberg in Lund (1941), not with a numerical computer, but by his arrangement of movable light-bulbs and photocells to measure the luminosity at each bulb and thereby estimate the gravitational force. A decade later, and with the arrival of the first programable computers, computations of galactic dynamics were performed, which were later transferred into a N-body simulation movie. I present here the background details for this work with a description of the important elements to note in the movie which may be retrieved at http://ttt.astro.su.se/~po .

The most characteristic high-energy phenomena in the Galactic center (GC) region is the presence of strong K-shell emission lines from highly ionized Si, S, Ar, Ca, Fe and Ni, which form the Galactic Center X-ray Emission (GCXE). These multiple lines suggest that the GCXE is composed of at least two plasmas with temperatures of ~1 and ~7 keV. The GCXE also exhibits the K-shell lines from neutral Si, S, Ar, Ca, Fe and Ni atoms. A debatable issue is the origin of the GCXE plasma; whether it is a diffuse plasma or integrated emission of many unresolved point sources such as cataclysmic variables and active binaries. Detailed spectroscopy for these lines may provide a reliable picture of the GCXE plasma. The origin of the K-shell lines from neutral atoms is most likely the fluorescence by X-rays from a putative past flare of Sgr A*. Therefore ASTRO-H may provide unprecedented data for the past light curve of Sgr A*. All these lines may provide key information for the dynamics of the GCXE, using possible Doppler shift and/or line broadening. This paper overviews these line features and the previous interpretation of their origin. We propose extended or revised science with the ASTRO-H observations of some select objects in the GC region.

The most characteristic high-energy phenomena in the Galactic center (GC) region is the presence of strong K-shell emission lines from highly ionized Si, S, Ar, Ca, Fe and Ni, which form the Galactic Center X-ray Emission (GCXE). These multiple lines suggest that the GCXE is composed of at least two plasmas with temperatures of ~1 and ~7 keV. The GCXE also exhibits the K-shell lines from neutral Si, S, Ar, Ca, Fe and Ni atoms. A debatable issue is the origin of the GCXE plasma; whether it is a diffuse plasma or integrated emission of many unresolved point sources such as cataclysmic variables and active binaries. Detailed spectroscopy for these lines may provide a reliable picture of the GCXE plasma. The origin of the K-shell lines from neutral atoms is most likely the fluorescence by X-rays from a putative past flare of Sgr A*. Therefore ASTRO-H may provide unprecedented data for the past light curve of Sgr A*. All these lines may provide key information for the dynamics of the GCXE, using possible Doppler shift and/or line broadening. This paper overviews these line features and the previous interpretation of their origin. We propose extended or revised science with the ASTRO-H observations of some select objects in the GC region.

We propose a new dynamical mechanism to account for the bar off-centering observed in many barred galaxies. It is based on the presence of a m=1 density wave, non-linearly excited by the strong m=2 component due to the linearly unstable bar and by a m=3 mode. N-body simulations suggest that this mechanism is at work in the centers of galaxies, and provide a natural explanation by spontaneously producing bar off-centering which amounts to several tens of parsecs.

We present Sauron 2D spectrography of the central 1.5 kpc of the nearby Sey2 galaxy NGC1068, encompassing the well-known NIR inner bar. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their 2D distribution and kinematics. The [OIII] and Hbeta emission lines exhibit very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inwards streaming motions are observed in both the Hbeta and [OIII] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and h3 fields. We re-examined the long-slit data of Shapiro et al (2003) using pPXF: a strong decoupling of h3 is revealed, and the central decrease in h4 hinted in the Sauron data is confirmed. These data also suggest that NGC1068 is a good candidate for a so-called sigma-drop. We confirm the possible presence of two pattern speeds. We also examine the stellar kinematics of bars formed in N-body+SPH simulations built from axisymmetric initial conditions. These successfully reproduce a number of properties observed in the 2D kinematics of NGC1068, and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models suggest that the inner bar could drive a significant amount of gas down to a scale of ~300 pc. This is consistent with the interpretation of the sigma-drop in NGC1068 being the result of central gas accretion followed by an episode of star formation.

We study the ionization, thermal structure, and dynamics of AGN flows which are partially shielded from the central continuum. We utilize detailed non-LTE photoionization and radiative transfer code using exact (non-Sobolev) calculations. We find that shielding has a pronounced effect on the ionization, thermal structure, and the dynamics of such flows. Moderate shielding is especially efficient in accelerating flows to high velocities since it suppresses the ionization level of the gas. The ionization structure of shielded gas tends to be distributed uniformly over a wide range of ionization levels. In such gas, radiation pressure due to trapped line photons can dominate over the thermal gas pressure and have a significant effect on the thermal stability of the flow. Heavily shielded flows are driven mainly by line radiation pressure, and so line locking has a large effect on the flow dynamics. We show that the observed ``L_\alpha ghost'' is a natural outcome in highly ionized flows that are shielded beyond the Lyman limit. We suggest that high velocity AGN flows occupy only a small fraction of the volume and that their density depends only weakly on the velocity field.

Self-consistent hybrid N-body and SPH simulations are used to give a new and coherent interpretation of the main features standing out from the HI and CO longitude-velocity observations within the Galactic bar. In particular, the traces of the gas associated to the Milky Way's dustlanes can be reliably identified and the 3-kpc arm appears as a gaseous stream rather than a density wave. The bar and the gaseous nuclear ring in the simulations undergo synchronised and long lived oscillations around the centre of mass, and the gas flow always remains non-stationary, suggesting a transient nature of the observed gas kinematics.

The purpose of this paper is to study the relations between different concepts of dispersive solution for the Vlasov-Poisson system in the gravitational case. Moreover we give necessary conditions for the existence of partially and totally dispersive solutions and a sufficient condition for the occurence of statistical dispersion. These conditions take the form of inequalities involving the energy, the mass and the momentum of the solution. Examples of dispersive and non-dispersive solutions--steady states, periodic solutions and virialized solutions--are also considered.

Using an equation of motion for a self-gravitating filament, we show how galactic spiral arms might be created and sustained. We find that the combination of differential rotation of the galactic disk and the self-gravity of the arm (as given by the equation) leads to a rotating spiral structure. Moreover, using this analysis, we then find a second differential equation that explicitly relates this spiral structure to the rotation curve of the galaxy -- it connects several factors, including spiral shape and pattern speed. We also describe a simple many-body numerical experiment that supports our approach. The findings are with consistent with observational evidence concerning arm structure and rotation curves, including leading arm structures.

Using an equation of motion for a self-gravitating filament, we show how galactic spiral arms might be created and sustained. We find that the combination of differential rotation of the galactic disk and the self-gravity of the arm (as given by the equation) leads to a rotating spiral structure. Moreover, using this analysis, we then find a second differential equation that explicitly relates this spiral structure to the rotation curve of the galaxy -- it connects several factors, including spiral shape and pattern speed. We also describe a simple many-body numerical experiment that supports our approach. The findings are with consistent with observational evidence concerning arm structure and rotation curves, including leading arm structures.

Using an equation of motion for a self-gravitating filament, we show how galactic spiral arms might be created and sustained. We find that the combination of differential rotation of the galactic disk and the self-gravity of the arm (as given by the equation) leads to a rotating spiral structure. Moreover, using this analysis, we then find a second differential equation that explicitly relates this spiral structure to the rotation curve of the galaxy -- it connects several factors, including spiral shape and pattern speed. We also describe a simple many-body numerical experiment that supports our approach. The findings are with consistent with observational evidence concerning arm structure and rotation curves, including leading arm structures.

The kinetic motion of the stars of a galaxy is considered within the framework of a relativistic scalar theory of gravitation. This model, even though unphysical, may represent a good laboratory where to study in a rigorous, mathematical way those problems, like the influence of the gravitational radiation on the dynamics, which are still beyond our present understanding of the physical model represented by the Einstein--Vlasov system. The present paper is devoted to derive the equations of the model and to prove the existence of spherically symmetric equilibria with finite radius.

The network of cosmic ray observatories reaching across the heliosphere has given new insight into the process of solar modulation, establishing that the decreases occur principally in the outer heliosphere and are produced by interplanetary flow systems; that the hysteresis effects appear to be produced by changes in the rigidity dependence of the diffusion coefficient and that the predicted effects on the cosmic ray gradients associated with the reversal of the solar magnetic field polarity are not observed.

Using strong lensing data Milgrom's MOdified Newtonian Dynamics (MOND) or its covariant TeVeS (Tensor-Vector-Scalar Theory) is being examined here as an alternative to the conventional $\Lambda$CDM paradigm. We examine 10 double-image gravitational lensing systems, in which the lens masses have been estimated by stellar population synthesis models. While mild deviations exist, we do not find out that strong cases for outliers to the TeVeS theory.

The Galactic Centre (GC) is a unique place to study the extreme dynamical processes occurring near a super-massive black hole (SMBH). Here we investigate the role of supernova (SN) explosions occurring in massive binary systems lying in a disc-like structure within the innermost parsec. We use a regularized algorithm to simulate 30,000 isolated three-body systems composed of a stellar binary orbiting the SMBH. We start the integration when the primary member undergoes a SN explosion, and we analyze the impact of SN kicks on the orbits of stars and compact remnants. We find that SN explosions scatter the lighter stars in the pair on completely different orbits, with higher eccentricity and inclination. In contrast, stellar-mass black holes (BHs) and massive stars retain memory of the orbit of their progenitor star. Our results suggest that SN kicks are not sufficient to eject BHs from the GC. We thus predict that all BHs that form in situ in the central parsec of our Galaxy remain in the GC, building up a cluster of dark remnants. In addition, the change of NS orbits induced by SNe may partially account for the observed dearth of NSs in the GC. About 40 per cent of remnants stay bound to the stellar companion after the kick; we expect up to 70 per cent of them might become X-ray binaries through Roche-lobe filling. Finally, the eccentricity of some light stars becomes > 0.7 as an effect of the SN kick, producing orbits similar to those of the G1 and G2 dusty objects.

We consider the consequences of applying general relativity to the description of the dynamics of a galaxy, given the observed flattened rotation curves. The galaxy is modeled as a stationary axially symmetric pressure-free fluid. In spite of the weak gravitational field and the non-relativistic source velocities, the mathematical system is still seen to be non-linear. It is shown that the rotation curves for various galaxies as examples are consistent with the mass density distributions of the visible matter within essentially flattened disks. This obviates the need for a massive halo of exotic dark matter. We determine that the mass density for the luminous threshold as tracked in the radial direction is $10^{-21.75}$ kg$\cdot$m$^{-3}$ for these galaxies and conjecture that this will be the case for other galaxies yet to be analyzed. We present a velocity dispersion test to determine the extent, if of any significance, of matter that may lie beyond the visible/HI region. Various comments and criticisms from colleagues are addressed.

B,V CCD frames have been used to derive surface brightness profiles for NGC 3201 out to ~18 arcmin. A total of 857 radial velocities with median precision ~1 km/s for 399 member giants have been used to trace the velocity dispersion profile out to 32' (the approximate tidal radius from fits of single-mass, isotropic King-Michie models to the cluster surface brightness profiles). The median difference in radial velocity for stars on either side of an imaginary axis moved through the cluster in 1 degree steps shows a significant maximum amplitude of 1.22+/-0.25 km/s. We discuss possible explanations of this result, including: (1) cluster rotation; (2) preferential stripping of stars on prograde orbits near the limiting radius; (3) the projection of the cluster space velocity onto the plane of the sky and (4) a slight drift in the velocity zero point. It is difficult to identify the primary cause of the observed velocity field structure unambiguously, and we suspect that all of the above processes may play a role. The B,V surface brightness profiles and radial velocities have been modeled with single- & multi-mass King-Michie models and nonparametric techniques. The density and M/L profiles show good agreement over 1.5

The long-term evolution of stellar orbits bound to a massive centre is studied in order to understand the cores of star clusters in central regions of galaxies. Stellar trajectories undergo tiny perturbation, the origin of which is twofold: (i) gravitational field of a thin gaseous disc surrounding the galactic centre, and (ii) cumulative drag due to successive interactions of the stars with material of the disc. Both effects are closely related because they depend on the total mass of the disc, assumed to be a small fraction of the central mass. It is shown that, in contrast to previous works, most of the retrograde (with respect to the disc) orbits are captured by the central object, presumably a massive black hole. Initially prograde orbits are also affected, so that statistical properties of the central star cluster in quasi-equilibrium may differ significantly from those deduced in previous analyses.

The Galactic centre (GC) is a unique place to study the extreme dynamical processes occurring near a super-massive black hole (SMBH). Here we simulate a large set of binaries orbiting the SMBH while the primary member undergoes a supernova (SN) explosion, in order to study the impact of SN kicks on the orbits of stars and dark remnants in the GC. We find that SN explosions are efficient in scattering neutron stars and other light stars on new (mostly eccentric) orbits, while black holes (BHs) tend to retain memory of the orbit of their progenitor star. SN kicks are thus unable to eject BHs from the GC: a cusp of dark remnants may be lurking in the central parsec of our Galaxy.

We show that a cosmological negative spatial curvature can account for both a recently identified phenomenological imprint of the global Hubble flow on galactic rotation curves and for the recently detected cosmic repulsion and cosmic acceleration. Even though such a negative curvature (a curvature which a galactic rest frame observer recognizes as a universal linear potential which gives rise to a universal acceleration) is only achievable in standard gravity by extreme fine tuning, nonetheless, it is naturally realizable in conformal gravity, a currently viable, fully covariant, candidate alternate gravitational theory.

Observations of the Galactic Centre show evidence of one or two disc-like structures of very young stars orbiting the central super-massive black hole within a distance of a few 0.1 pc. A number of analyses have been carried out to investigate the dynamical behaviour and consequences of these discs, including disc thickness and eccentricity growth as well as mutual interaction and warping. However, most of these studies have neglected the influence of the stellar cusp surrounding the black hole, which is believed to be 1-2 orders of magnitude more massive than the disc(s). By means of N-body integrations using our bhint code, we study the impact of stellar cusps of different compositions. We find that although the presence of a cusp does have an important effect on the evolution of an otherwise isolated flat disc, its influence on the evolution of disc thickness and warping is rather mild in a two-disc configuration. However, we show that the creation of highly eccentric orbits strongly depends on the graininess of the cusp (i.e. the mean and maximum stellar masses): While Chang (2009) recently found that full cycles of Kozai resonance are prevented by the presence of an analytic cusp, we show that relaxation processes play an important role in such highly dense regions and support short-term resonances. We thus find that young disc stars on initially circular orbits can achieve high eccentricities by resonant effects also in the presence of a cusp of stellar remnants, yielding a mechanism to create S-stars and hyper-velocity stars. Furthermore, we discuss the underlying initial mass function (IMF) of the young stellar discs and find no definite evidence for a non-canonical IMF.

AGN feedback now appears as an attractive mechanism to resolve some of the outstanding problems with the "standard" cosmological models, in particular those related to massive galaxies. To directly constrain how this may influence the formation of massive galaxies near the peak in the redshift distribution of powerful quasars, z~2, we present an analysis of the emission-line kinematics of 3 powerful radio galaxies at z~2-3 (HzRGs) based on rest-frame optical integral-field spectroscopy obtained with SINFONI on the VLT. HzRGs are among the most massive galaxies, so AGN feedback may have a particularly clear signature. We find evidence for bipolar outflows in all HzRGs, with kinetic energies that are equivalent to 0.2% of the rest-mass of the supermassive black hole. Velocity offsets in the outflows are ~800-1000 km s^-1 between the blueshifted and redshifted line emission, FWHMs ~1000 km s^-1 suggest strong turbulence. Ionized gas masses estimated from the Ha luminosity are of order 10^10 M_s, similar to the molecular gas content of HzRGs, underlining that these outflows may indicate a significant phase in the evolution of the host galaxy. The total energy release of ~10^60 erg during a dynamical time of ~10^7 yrs corresponds to about the binding energy of a massive galaxy. Geometry, timescales and energy injection rates of order 10% of the kinetic energy flux of the jet suggest that the outflows are most likely driven by the radio source. The global energy density release of ~10^57 erg s^-1 Mpc^-3 may also influence the subsequent evolution of the HzRG by enhancing the entropy and pressure in the surrounding halo and facilitating ram-pressure stripping of gas in satellite galaxies that may contribute to the subsequent mass assembly of the HzRG through low-dissipation "dry" mergers.

I describe the design, implementation, and usage of galpy, a Python package for galactic-dynamics calculations. At its core, galpy consists of a general framework for representing galactic potentials both in Python and in C (for accelerated computations); galpy functions, objects, and methods can generally take arbitrary combinations of these as arguments. Numerical orbit integration is supported with a variety of Runge-Kutta-type and symplectic integrators. For planar orbits, integration of the phase-space volume is also possible. galpy supports the calculation of action-angle coordinates and orbital frequencies for a given phase-space point for general spherical potentials, using state-of-the-art numerical approximations for axisymmetric potentials, and making use of a recent general approximation for any static potential. A number of different distribution functions (DFs) are also included in the current release; currently these consist of two-dimensional axisymmetric and non-axisymmetric disk DFs, a three-dimensional disk DF, and a DF framework for tidal streams. I provide several examples to illustrate the use of the code. I present a simple model for the Milky Way's gravitational potential consistent with the latest observations. I also numerically calculate the Oort functions for different tracer populations of stars and compare it to a new analytical approximation. Additionally, I characterize the response of a kinematically-warm disk to an elliptical m=2 perturbation in detail. Overall, galpy consists of about 54,000 lines, including 23,000 lines of code in the module, 11,000 lines of test code, and about 20,000 lines of documentation. The test suite covers 99.6% of the code. galpy is available at http://github.com/jobovy/galpy with extensive documentation available at http://galpy.readthedocs.org/en/latest .

One of the present concepts for the onset of massive star formation is the Kennicutt criterion. This relates the onset of massive star formation to a general gravitational instability of the gas disks of spiral galaxies. It is often overlooked, however that such gravitational instabilities of the gas disks have severe implications for the overall stability of the gas and star disks of spiral galaxies. I show by numerical simulations of the evolution of a combined gas and star disk that the violation of the stability condition induces violent dynamical evolution of the combined system. In particular the star disk heats up on time scales less than a Gyr to unrealistic high values of the Toomre stability parameter Q. The morphologies of both the star and gas disk resemble then no longer observed morphologies of spiral galaxies. Star formation of stars on low velocity dispersion orbits would lead to dynamical cooling of the disks to more realistic states. However, the required star formation rate is extremely high.

We review the available methods for estimating actions, angles and frequencies of orbits in both axisymmetric and triaxial potentials. The methods are separated into two classes. Unless an orbit has been trapped by a resonance, convergent, or iterative, methods are able to recover the actions to arbitrarily high accuracy given sufficient computing time. Faster non-convergent methods rely on the potential being sufficiently close to a separable potential and the accuracy of the action estimate cannot be improved through further computation. We critically compare the accuracy of the methods and the required computation time for a range of orbits in an axisymmetric multi-component Galactic potential. We introduce a new method for estimating actions that builds on the adiabatic approximation of Sch\"onich & Binney (2012) and discuss the accuracy required for the actions, angles and frequencies using suitable distribution functions for the thin and thick discs, the stellar halo and a star stream. We conclude that for studies of the disc and smooth halo component of the Milky Way the most suitable compromise between speed and accuracy is the St\"ackel Fudge, whilst when studying streams the non-convergent methods do not offer sufficient accuracy and the most suitable method is computing the actions from an orbit integration via a generating function. All the software used in this study can be downloaded from https://github.com/jls713/tact.

We simultaneously integrate in a numerical way the equations of motion of both the Magellanic Clouds (MCs) in MOND, MOG and CDM for -1

Electromagnetic observations over the last 15 years have yielded a growing appreciation for the importance of supermassive black holes (SMBH) to the evolution of galaxies, and for the intricacies of dynamical interactions in our own Galactic center. Here we show that future low-frequency gravitational wave observations, alone or in combination with electromagnetic data, will open up unique windows to these processes. In particular, gravitational wave detections in the 10^{-5}-10^{-1} Hz range will yield SMBH masses and spins to unprecedented precision and will provide clues to the properties of the otherwise undetectable stellar remnants expected to populate the centers of galaxies. Such observations are therefore keys to understanding the interplay between SMBHs and their environments.

Recent observations suggest ongoing planet formation in the innermost parsec of our Galaxy. The super-massive black hole (SMBH) might strip planets or planetary embryos from their parent star, bringing them close enough to be tidally disrupted. We investigate the chance of planet tidal captures by running three-body encounters of SMBH-star-planet systems with a high-accuracy regularized code. We show that tidally captured planets have orbits close to those of their parent star. We conclude that the final periapsis distance of the captured planet from the SMBH will be much larger than 200 AU, unless its parent star was already on a highly eccentric orbit.

I selectively review the various dynamical scenarios that have been explored to date, especially those that illustrate the conundrums. In short, although the existence of asymmetries are convincing enough, the interpretation remains ambiguous. A coherent picture for the Milky Way asymmetries is an obvious lack; each mechanism is considered independently of all others. With this motivation, I will present a nonstandard picture which has the potential to explain some of the signatures and a few of the conundrums. Moreover, it illustrates global features are dynamically connected and I believe that it is time to revisit the Milky Way in this context. Finally, I will end with a wish list for future work---both observational and theoretical---designed to help us pin down the Milky Way.

We investigate gas dynamics in the presence of a double inner Lindblad resonance within a barred disk galaxy. Using an example of a prominent spiral, M100, we reproduce the basic central morphology, including four dominant regions of star formation corresponding to the compression maxima in the gas. These active star forming sites delineate an inner boundary (so-called nuclear ring) of a rather broad oval detected in the near infrared. We find that inclusion of self-gravitational effects in the gas is necessary in order to understand its behavior in the vicinity of the resonances and its subsequent evolution. The self-gravity of the gas is also crucial to estimate the effect of a massive nuclear ring on periodic orbits in the stellar bar.