High-resolution optical and NIR observations are used to constrain a dynamical model of the circumnuclear star forming (SF) region in the barred galaxy M100 (NGC 4321). Small leading arms observed in our K-band image of the nuclear region have been reproduced in numerical modeling of M100, a galaxy with a double inner Lindblad resonance (ILR). We also present preliminary optical and NIR observations of NGC 6951: a barred galaxy with circumnuclear SF showing a distinctly different behavior to M100 at 2.2µm.

We have recently obtained some interesting results on the global stability characteristics of gaseous and stellar systems using a free–energy variational formulation and Ginzburg–Landau phase transition theory (Christodoulou et al. 1995a, b). For m = 2 nonaxisymmetric modes in particular, we have been able to formulate a new, robust, global stability criterion (Christodoulou, Shlosman, & Tohline 1995, hereafter CST) that avoids many of the problems that plagued the well–known Ostriker & Peebles (1973) criterion. In this article, we briefly summarize the conclusions from the above–cited investigations and we proceed to comment on the stability properties of some interesting stellar models that were discussed during this conference and that are not trivially understood in terms of the new stability criterion.

A barred galaxy is mainly built of billions of stars moving on different orbits. Understanding of the orbital structure is essential for the interpretation of observations. The orbital structure can be investigated using analytical models and N-body simulations. This paper presents a method to classify orbits found in N-body simulations, i.e. orbits in a time-dependent potential. I present some results about mass loss and mass gain of bars and the influence of a bulge.

Gas dynamics induced by bars involves large-scale shocks. The shock fronts may be curved, especially near the bar edges. Evolution of the curved shocks can lead to effective compression of the interstellar gas which produces favorable conditions for violent star formation in the vicinity of bars.

In this review we discuss the phenomenon of counterrotation, observed in ~40 apparently normal galaxies where gas or stars are rotating in a direction opposite to the main stellar body. It appears in all morphological types, from ellipticals to spirals or irregulars.

The problem of the origin and the evolution of counterrotation is discussed, in the wider frame of the galaxies accreting matter from their environment (e.g., minor-axis dust-lane ellipticals or polar-ring S0s). Various sources of matter appear to be candidates for the production of the counterrotation.

Due to the tendency of the bar potential to populate particular families of orbits, some cases of counterrotation found in barred galaxies are interpreted as intrinsic to barred galaxies.

A massive gaseous disk in the central region of a galaxy sensitively responds to a weakly distorted potential, and a large amount of gas can be fed into within 1/20 of the core radius of the potential in several 107 yr. The ILRs, the dissipative nature of the gas, and the self-gravity of the gas are essential for triggering this effective fueling. We also found that a counterrotating gaseous core can be formed as a result of the fueling. Our result suggests that the merger of galaxies is not the only way to form the observed counterrotating core in galaxies.

We discuss the “rotation” curves of SB0 galaxies with self-consistent models constructed with Schwarzschild’s method. Their distribution functions are compared with that of N-body simulations.

This contribution presents a general discussion of special topics on barred galaxies by participants in the meeting.

Some of the classical seyferts are observed to be prototypical ovals, e.g. NGC 1068 and 4151 (e.g., Bosma 1981; Kormendy 1982; Scoville et al. 1988). Such a non-axisymmetric potential corresponding to an oval disk can produce inward flow of gas and induce mild activity. To test the efficiency of this process, we study a collision between a face-on spiral with a high gaseous content and an equally massive compact elliptical, under marginally bound conditions, as such encounters are most frequent.

We model the spiral galaxy by an exponential model disk (of radius R) with a (static) thickness and scale length α = 4/R and a spherical polytropic bulge (n=0,3,4, equally weighted combination) containing 1/3 of the mass (cf. Chatterjee 1990); about 20% of the mass of the disk contains gas particles. The elliptical is modeled identically as the bulge. The gravitational potential is softened with softening constants of ∊ = r∘/5, r∘/3, and 0.8r∘, for the bulge of the spiral as well as the elliptical, stellar and gaseous components of the disk, respectively. Here r∘ is the radius containing 75% of the total mass of the galaxy in question, while the mutual gravitational interaction is softened with a softening constant of r∘/4.

By including counterrotating angular momentum in two-dimensional galactic disk simulations, we are able to create counterrotating bar modes. Over the period of several dynamical times, the counterrotating inner bar is shown to reverse its pattern direction, oscillate around the primary bar and finally align with it.

The question of bars within bars has been reviewed by Friedli and Martinet (1993), who have also performed N-body simulations to produce nested bars. They propose that if a system of embedded bars is effective in transporting gas to the galactic center (Shlosman et al. 1989), then it is perhaps a step in the secular evolution of barred galaxies. In order to pursue this interesting proposition, and also because observational evidence for the existence of secondary bars is mounting (e.g. Buta & Crocker 1993; Shaw et al. 1993, Wozniak et al. 1995), it is important to understand the stellar kinematics in such systems.

We investigate the dynamical response of stellar orbits in a rotating barred galaxy potential to the perturbation by a nuclear gaseous ring. The change in 3D periodic orbit families is examined as the gas accumulates near the inner Lindblad resonance. It is found that the x2/x3 loop extends to higher Jacobi energy and a vertical instability strip forms in each family. These strips are connected by a symmetric/anti-symmetric pair of 2:2:1 3D orbital families. A significant distortion of the x1 orbits is observed in the vicinity of the ring, which leads to the intersection between orbits over a large range of the Jacobi integral. We also find that a moderately elliptical ring oblique to the stellar bar produces significant phase shifts in the x1 orbital response.

NGC 5850 is a large, nearby SB(r)b spiral that is an apparent member of the NGC 5846 group of galaxies (de Vaucouleurs 1975; Turner & Gott 1976). The mean corrected redshift of this group is ≈1900 km s−1 (Haynes & Giovanelli 1991). We have obtained broadband imaging and VLA HI interferometry of this galaxy as part of a general study of its properties. The most noteworthy characteristic of the galaxy is a severe distortion of the outer regions. This distortion is most likely due to an interaction with another member of the group, possibly NGC 5846 or its companion NGC 5846A, which are only 10' to the northwest. In this paper we summarize some of the results of the optical and HI analysis, and highlight the effects of the interaction.

Recently, bars have become a favored mechanism for transporting material at larger radii towards the nuclei of active galaxies, with the possibility of inflowing gas (on kiloparsec scales) accumulating in circumnuclear rings, bar-like features or structures reminiscent of spiral arms. In addition, it seems clear that interactions play some role in the triggering and fuelling of nuclear activity, as well as in the formation and evolution of galactic bars. NGC 3227 is a barred Seyfert galaxy which appears to be interacting with the nearby elliptical galaxy NGC 3226. The NGC 3227 system thus appears to be an excellent ”laboratory case“ in which to study the relationship between the bar phenomenon, and an active nucleus in an interacting system.

An estimate for the slow bar instability boundary for a generalized disk polytropic model is derived. The effects of a spherical halo are studied: it turns out that a halo can be favorable to this instability (at the same time suppressing the bending instability).

Here we present a study of the structural components of the barred galaxy NGC 5850 using U, B and I photometry. After subtracting a bulge+disk model from the observed image, we obtain the bar and other non-axisymmetric structures. We determine the position of the ILR from the ellipticity and position angle profiles of the isophotes.

We have made test particle simulations of the gas component in barred galaxies. The potential consists of two parts: an axisymmetric isochrone potential

and a bar potential Φ1(r, θ) = Φb(r)cos(2θ), where

The bar strength, q, and scalelength, a, are chosen so that the relative nonaxisymmetric force reaches its maximum, 10%, at the distance which is 83% of the corotation radius. The potential and its scaling are the same as in Schwarz (1981).

Deviations from ellipticity in the bulges of edge-on disk galaxies, seen as ”boxy“, ”peanut-shaped“, or “X-shaped“ isophotes, have been known for some time (Jarvis 1986, Whitmore & Bell 1988). Contrary to earlier proposals that these features represent accreted material, recent numerical work (Combes et al. 1990; Raha et al. 1991) suggests that they form when the bars in barred galaxies experience a vertical bending instability and deform out of the disk plane. We have found this latter mechanism at work in simulations in which a bar is induced when a large disk galaxy accretes a small companion galaxy, thus incorporating the mechanism into the evolutionary framework of galaxy interactions. In support of this picture we present observations of Hickson 87a, an edge-on S0 galaxy whose morphological peculiarities exactly match those seen in the simulation.

We present Fabry-Perot observations of the velocity field of gas in the barred spiral NGC 4123, and 2-D hydrodynamical simulations of the gas flow in model potentials derived from I-band photometry. The simulated gas flow is quite sensitive to the details of the potential, which enables us to constrain parameters such as the M/LI of the bar and the bar pattern speed. The observations confirm that the dust lanes along the leading edges of the bar are the locations of shocks. Requiring models to produce shocks with the correct alignment constrains the Lagrange point L1 (corotation) to be at a radius 1.1 – 1.4 times the semimajor axis of the bar, i.e. the bar is a fast rotator.

We calculate the two-point correlation function for a sample of ringed galaxies. Results are similar to that of general field galaxies. We also find evidence that these galaxies form very large scale structures.