The detailed investigation of the activity and dynamics in NGC 7479 confirms the importance of understanding individual galaxies. We have discovered an S-shaped emission structure in 21 cm continuum. This detection together with strong nuclear 10 μm and Hα emission may imply the existence of a central massive black hole. We also address the origin of the asymmetric spiral structure in NGC 7479. The lack of any visible companion and the unperturbed H I velocity field suggest that the asymmetry has an internal origin.

We have made HI observations of an early type, NGC 1398 (SBab(r)I), and a late type barred system, NGC 3319 (SBc(s)II.4). NGC 1398 is a beautifully symmetric galaxy with a bright stellar bulge, bar and inner ring and tightly wound spiral arms (also classified as an R1 double outer pseudoring). In HI the spiral structure is strong but the center shows a sharp depletion. In contrast, NGC 3319 has an asymmetric appearance and irregular spiral structure. It is rich in its central HI with a gas bar and spiral arms, both of which are highlighted by prominent HII regions. We attempt to determine the pattern speeds of the galaxies and to explore the differences between early and late type systems.

We present results of numerical simulations of bar-unstable disks that include a dissipative gas component. The simulations have been carried out using a two-dimensional polar grid for the force calculations. The gas component has been modelled as a collection of finite-sized particles that dissipate a fraction of their relative motion during collisions.

Evidence from a variety of sources points towards the existence of a bar in the central few kpc of the Galaxy. The measurements roughly agree on the direction of the bar major axis, but other parameters (axis ratio, size, pattern speed) are still poorly determined. Current dynamical models are limited by the quality of hydro simulations, the degeneracy of stellar orbit models, stellar-kinematic data and the significant lopsidedness of the central kpc. Microlensing promises new constraints on the mass distribution in the bulge/bar region.

The dynamics of formation and evolution of structure in barred galaxies is subtle and will require many and detailed observations to discriminate between the alternative hypotheses. Why should someone interested in such problems consider the Milky Way? In terms of data volume, our knowledge of the Milky Way is vast and the availability of detail is its major advantage. In principle, one can study morphological details such as orientations, strengths of asymmetries and kinematics details such as velocity field/pattern speeds using a wide variety of tracers. To illustrate, theorists have not converged on a single mechanism to explain bars (witness the instability vs. secular formation debate). It is possible that both operate in different regimes depending on internal or external influences: internally, triaxialities and misalignments in the bulge, spheroid or halo can apply torques and drive angular momentum waves which saturate to form a bar; and externally, satellite galaxies can exchange orbital angular momentum with its disturbance which has the similar effect. In short, if the Galaxy is indeed barred, it may hold clues to some of the detailed problems posed at this meeting.

We present a 3D N-body simulation of the Milky Way including 4 × 105 star- and dark-like particles and 2 × 104 gas particles, initially distributed according to an axisymmetric, observationally constrained, mass model. The whole system is self-gravitating and the gas hydrodynamics is solved using the SPH method. The simulation leads to the spontaneous formation of a central bar that strongly affects the gas dynamics. We compute (l – V) diagrams for both the gaseous and the stellar particles as a function of the angle of the bar with respect to the observer and compare the results for the gas with HI and CO observations.

Part of a large survey of the inner galactic Plane (|ℓ| < 45° and |b| < 3° total) in the OH 1612MHz line in search for OH/IR stars is analyzed. We find strong evidence for a central m=2 distortion based on geometrical considerations. The observed deviation from axisymmetry cannot be explained by lopsidedness and agrees with other recent models of the galactic Bar on length, inclination and axis ratio.

It is shown that slopes of p(R) = Ω(R) ± κ(R)/m curves at Lindblad resonances determine the widths of resonance regions. The ability of galactic disks to respond to torques exerted at ILRs by perturbers (bar, density wave, galaxy-satellite, etc.) is determined by the widths of inner Lindblad resonances (ILRs). Widths of ILRs vary along the Hubble sequence of normal and barred galaxies. Galaxies having the bulge to disk ratio of masses and radii similar to the Milky Way could have wide ILRs if they are formed at the region of 2-4 kpc from their centers. A wide range of possible perturbers with pattern speeds 4≤ Ωp ≤ 26 km s≤1 kpc−1 could excite an ILR at this region of the Milky Way. Probably, the ILR of Milky Way’s grand design is located in the same region. The hole in the galactic H2 disk is also located in this region. The mechanism responsible for the origin of this hole could be similar to that opening gaps in planetary rings.

The color-magnitude diagrams of ~ 1 × 106 stars obtained for 19 fields towards the Galactic bulge with the OGLE project reveal a well-defined population of bulge red clump stars. We found that the distributions of the extinction-adjusted apparent magnitudes of red clump stars in fields lying at ι = ±5° in galactic longitude differ by ∼ 0.4 mag. A plausible explanation of this observed difference in the luminosity distribution is that the Galactic bulge is a triaxial structure, or a bar, which is inclined to the line of sight by no more than 45°. The part of the bar at the positive galactic longitude is closer to us. Work is now under way to model the Galactic bar by fitting the observed luminosity functions in the red clump region for various fields. Preliminary results indicate that the angle of the inclination of the bar to the line of sight can be as small as ∼ 20°. Gravitational microlensing can provide us with additional constraints on the structure of the Galactic bar.

A self-consistent stellar dynamical model for the Galactic bar is constructed from about 500 numerically computed orbits with an extension of the Schwarzschild technique. The model fits the COBE found asymmetric boxy light distribution and the observed stellar kinematics of the bulge. The model potential is also consistent with the non-circular motions of the HI and CO velocity maps of the inner Galaxy. We also use the stellar bar model to construct an N-body model to study stability and a microlensing map towards the bulge, which can account for the observed optical depth and the event duration by the MACHO and OGLE collaborations. The technique used here can be applied to interpret light and velocity data of external bulges/bars and galactic nuclei.

Recently the bar model for our Galaxy has been an emerging consensus. Here, we investigate how a rotating bar-like bulge affects the global gas dynamics in a disk and compare the longitude-velocity (LV) maps from self-gravitating hydrodynamical simulations, which is based on Wada and Habe (1992), with observed maps of neutral hydrogen and carbon monoxide in the Galaxy. We found that the features on the numerical LV maps depend strongly on four factors: the pattern speed of the bar, the position angle of the Sun, the strength of the bar potential and the ratio of the gas mass to total dynamical mass. We conclude that our Galaxy has a rotating, weak, bar-like bulge (a/b ∼ 0.7) observed from nearly end on (θp < 20°). The allowed range of pattern speed of the bar is surprisingly narrow (19±5 km s−1 kpc−1) and is consistent with recent observations of bulge stars. Self-gravity of the interstellar matter is needed to account for the observed molecular ring at a radius of ∼ 4 kpc even if the gas mass fraction to the dynamical mass is small (about 5%).

The luminosity profiles perpendicular to the bar of the galaxy NGC 7479 display “shoulders”, which are observationally identified as an increase in the brightness profile (see Figure 1, right). In the literature (see e.g. Buta 1986), the presence of these features in other barred spirals has been reported. The “shoulders” have been attributed to annular structures resulting from the presence of a bar (Schwarz 1981, 1984, 1985), appearing at the OLR. Their stability and the precise modelling depends on the structural parameters of the bar. We attempt to test the plausibility of this theoretical interpretation using 2D photometry of the barred galaxy NGC 7479. The key parameter is the corotation radius (CR), defined as the galactocentric distance at which the gas and the shock wave corotate. From the CR all other Lindblad resonances can be obtained. Some of the techniques used to derive the CR are:

I review some of the more notable observational aspects of bars in galaxies. Key issues include the overall occurrence of bars, secular evolution of bars and bulges, the differences in bar properties with Hubble type, the role of bars in star formation and nuclear activity, and the evidence for a bar at the center of the Milky Way. These lead to a “wish list” of future observations.

Why do so many galaxies have bars? Why are bars so rugged? These questions, vital to understanding barred galaxies, have not been addressed in this Conference.

Numerical studies seem to have replaced analytic theory. But the bars in numerical studies may not be good models of real galaxies.