The ratio R of the corotation radius to the bar radius ranges from 1 to 1.8 in theoretical models that fit the observed dynamics of gas or stars in the bar and spiral regions of galaxies. Most models cluster around a ratio R = 1.2 for early type galaxies. This ratio confirms the bar-aligned orbit theory long held by Contopoulos and others, which requires that R < 1, but it also suggests that bars do not end exactly at corotation, as is often assumed, but significantly inside. The difference between R = 1 in the old interpretation and R = 1.2 or 1.4 in the fitted models is critical for our interpretation of bar-spiral morphologies. It appears that the bar-to-spiral transition in early Hubble types occurs between the inner 4:1 resonance and corotation, in the range corresponding to R = 1.55 to 1 for a flat rotation curve, because of orbit stochasticity where the 2m: 1 orbits in the x1 family cluster together in space. Corotation then occurs relatively far out in the arms, at an angle from the bar end that may exceed 60° for tightly wrapped spirals. This position sometimes corresponds to the crossing of a dust lane from inside the arms to outside (NGC 1300, NGC 1365) or to a spiral arm bifurcation as in non-barred galaxies. The relatively high value of R is also consistent with the identification of inner rings with the inner 4:1 resonance, outer rings with the outer Lindblad resonance, and offset bar dust lanes and nuclear rings with the inner Lindblad resonance. In contrast to this clear interpretation for early type galaxies, there is little consensus on the location of corotation in late type galaxies, which usually lack an inner Lindblad resonance interior to the bar. It is also not known whether late type spirals corotate with their bars, although this appears to be the case for early type galaxies based on the ubiquity and location of outer spirals and rings.

Analysis of ionized gas velocity fields in the circumnuclear regions of 13 normal spiral galaxies has shown that about half of them reveal a discrepancy between the kinematical axis at R < 2″ and the photometric or kinematical axes of the outer regions. This result indicates a high frequency of occurrence of non-axisymmetric gravitational potentials in the inner few hundred parsecs of galaxies. The possible nature of these minibars is discussed.

From a detailed photometric analysis together with some kinematical information for a sample of isolated spirals, we conclude that most of them host rings or bars, features generally explained as originating from a non-axisymmetrical component of the gravitational potential. In a previous study, we have determined that all the isolated spirals hosting an active nucleus show these kinds of non-axisymmetrical components, the presence of which could be connected with the nuclear activity in the form that they can be very effective in transporting gas into the central parts. Therefore, as non-active spirals show a similar behavior, a detailed analysis of the possible differences between the central regions of active and non-active isolated spirals is motivated.

We describe a kinematic measurement of the pattern speed in the classic SB0 galaxy NGC 936. While the practicalities of this method remain difficult, allowance for non-Gaussian velocity distributions enables more reliable measurements than hitherto possible. The bar of NGC 936 appears to end just inside its corotation radius.

Results of 3D-spectroscopy for the nearby Seyfert galaxy Mrk 573 obtained at the 6-m telescope with the scanning Fabry-Perot interferometer and the Multi-Pupil Field Spectrograph (MPFS) are presented. Emission lines images of the galaxy center demonstrate a complex structure of ENLR, coinciding with the radio data. An analysis of the velocity field shows that some gas structures do not lie in the plane of the galaxy. An explanation of the observed velocity field and gas distribution by radiation of a helical structure located inside an ionization cone is proposed.

The central (8″ × 8″) regions of the Seyfert galaxies Mrk 744 and NGC 4151 were studied by the 3D-spectroscopy method. There is evidence that a mini-bar (0.5–2 kpc) is present in the central regions of these galaxies, which provides transportation of gas of the disk to fuel the nucleus.

Galaxies with box/peanut-shaped (b/p) bulges have been known for some time (e.g., NGC 128 and NGC 7332 (Sandage 1961)). Observationally, b/p features are detected in edge-on systems, and are visible in images, contour maps, and brightness profiles as isophote sections that near minor axis are relatively flat and parallel to major axis (see Figure 1). Peanut-type bulges have isophotes indented at the intersection with the minor axis.

There have been several morphological surveys to date. The two most recent studies have found that about 20% of early-type galaxies and nearly 45% of all disk galaxies are b/p galaxies (see Shaw 1987, Dettmar 1989, and references therein) and that the b/p galaxy properties appear similar to normal spirals in the optical, radio, and infrared. A few kinematical studies have been done: b/p bulges are found to rotate more like disks than bulges (e.g., 150 km s−1 up to 6 kpc above the plane in NGC 128 (Jarvis 1990) and the velocities remain constant up to large z, implying cylindrical rotation (e.g., NGC 3079 has v constant out to 1.6 kpc (Shaw et al. 1993)).

We present CO(1-0) interferometer data with × spatial resolution and 13 km s−1 velocity resolution acquired at the Owens Valley Radio Observatory. These data reveal a clumpy circumnuclear ring of gas. We also find a central peak of CO within 2″ of the optical center. Deviations from circular motion are seen where the dust lanes along the leading edge of the bar intersect the nuclear ring, consistent with gas inflow along the bar. Hα maps of this galaxy show bright HII regions near the ends of this inflow region, indicating triggering of star formation by the inflow.

The circumnuclear (inner kiloparsec) regions of spiral galaxies are time-dependent systems whose morphology and dynamics can change significantly over less than a Hubble time. To develop an insight into this evolution it is important to study the fate of gas driven towards the central parts of a galaxy especially near the dynamical resonances. The panoply of CO morphologies displayed by the circumnuclear regions of starburst and nonstarburst galaxies such as NGC 3504, NGC 3351, NGC 7479, NGC 6951, etc, (Kenney, these proceedings) is not yet clearly understood. Another unsettled issue concerns the criteria for star formation in the circumnuclear region where, in contrast to the outer disk, the rotation curve is nearly solid-body and rises rapidly. These issues need to be resolved; the gas mass fraction, the radial variation of SFR (star formation rate) and its interplay with the gas kinematics can shed light not only on the temporal evolution of the circumnuclear CO morphology but also on secular evolution through the destruction and creation of new stellar components. For instance, stellar bars can be destroyed by an increase in the central gas mass concentration of a few % of the total galaxy mass while mechanisms to build or enhance a bulge by vertical scattering of the stars in a compact circumnuclear stellar disk have been proposed (Sellwood 1994, Pfenniger & Norman 1990). We have carried out a study of the circumnuclear region of NGC 4102 with these important issues in mind. NGC 4102, a LINER/HII, SABb spiral galaxy at a distance of 17 Mpc with a bar and/or lens feature qualifies as one of the most luminous nearby starbursts (Devereux 1989) and seems to be in a very early phase of evolution. The outflow timescale of the central starburst wind in NGC 4102, determined from optical spectroscopy of the ionized swept-up gas, is 106 years (Boer 1994), suggesting it is at an earlier evolutionary phase than M82 and NGC 253 whose outflow timescales are significantly larger.

The Seyfert 2 galaxy Mrk 533 has the morphological description of SA(r)bc pec in RC3 and SBb in UGC. It is a member of the compact group of galaxies H96. Radio observations (Unger et al. 1988) show three radio sources.

3-D observations with a Fabry-Perot scanning interferometer (the number of spectral channels is 32 by 0.44 Å, angular size of 1 px is , the accuracy of radial velocity determination is 10 km s−1) and multi-pupil integral spectrograph observations (the dispersion is 1.16 Å px−1, lens array is 10×16, angular size of each lens is × ) were obtained in the red spectral range at the 6-m telescope. The estimated seeing was about 2″. In the central region of the galaxy (r ≥ 5″, interferometer observations) the Hα line profile was fitted by two Gaussians. The first component, Kl, corresponds to the galaxy disk. The second component, K2, is visible only in the central part and is brighter than K1 in the same pixels. Profiles of Hα and [NII] Λ6584/48 (integral spectroscopy observations) were fitted by two Gaussians. They are a broad component in Hα and [NII] with FWHM ~ 1000 km s−1 and a narrow component of three times less FWHM. The lower spectral resolution of this observation made it impossible to separate the narrow component into the two ones visible in the Fabry-Perot observations.

We investigate the extent of the HI halo in five isolated SB galaxies featuring strong bars. VLA1 observations of these objects are used to determine the diameter ratio between the HI and the optical distribution. The mean diameter ratios D1.82/D(0) and DHI/D(0), for the sample presented here, are 1.1±0.1 and 1.2±0.1 respectively (1σ r.m.s.). For samples of various types, Bosma (1981) and Broeils (1992) find D1.82/D(0) = 2.2±1.1 and DHI/D(0) = 1.8±0.4 respectively. Our result thus could indicate compactness of the HI halo in galaxies with strong bars.

A sample of southern spiral galaxies are being observed at 20 and 13 cm with the Australia Telescope Compact Array in order to look for examples of anomalous outflows from the nuclear region. In this paper we discuss the radio continuum maps of the three barred spiral galaxies observed to date.

Bars are thought to play a crucial role in the fueling of AGN (see e.g., Mundell et al., in these proceedings and references therein), and as part of a project to investigate this, we have studied the neutral hydrogen structure in the bar of the Seyfert 1.5 galaxy NGC 4151.

High-sensitivity VLA observations have enabled us to image the neutral hydrogen emission from the bar of NGC 4151 in unprecedented detail, and is a continuation of the work by Pedlar et al. (1992).

Figure 1 shows images of integrated neutral hydrogen emission. The large scale emission extends over approximately 20 kpc and the outer part consists of a well-defined two-armed spiral which originates from a fat bar at a radius of about 5 kpc. The bar shows complex structure, including two sharp features which are reminiscent of the shocks seen in many simulations, e.g., Athanassoula (1992). These features appear to join the central 1-kpc ring discovered by Vila-Vilaró et al. (1994), and for which there appears a partial counterpart in neutral hydrogen emission.

We present a preliminary analysis of B- and I-band CCD images and Rutgers imaging Fabry–Perot Hα interferometry of the galaxy NGC 3081. We find that the outer R1 and inner ring are both intrinsically oval. We derive a bar pattern speed from the velocity field.

Since molecular gas fuels AGNs and molecular clouds form stars, understanding of molecular gas dynamics is a key to the understanding of active phenomena (such as starbursts and AGNs) in galactic nuclei. To study gas dynamics in weakly barred galaxies, we made CO interferometry (to trace gas) and NIR imaging (to trace stars) toward two nearby SAB galaxies M100 and M94. Each galaxy has a small stellar nuclear bar and also has an outer bar or oval distortion, thus suitable for the study of gas dynamics in a barred gravitational potential. Observations were made using Nobeyama Millimeter Array (NMA) and the IRcamera PICNIC installed at the ISAS 1.3 m telescope.

NGC 1433 is a nearly face-on prototypical ringed, barred galaxy. It has a nuclear ring, an inner ring and an outer pseudoring. Also present are symmetrical spiral arcs, also called “plumes”, leading the central bar. Based on a study using multicolor surface photometry and Hα Fabry-Perot interferometry, Buta (1986) was able to associate each of the ring features with a specific orbital resonance. NGC 6300, having almost an identical Hubble type and distance to that of NGC 1433, provides for an ideal comparison. It has no nuclear or outer rings. However, the inner ring is quite broad and dusty (Buta 1987). Radio continuum data were obtained with the Australia Telescope Compact Array (ATCA) at 1.38 GHz (bandwidth = 128.0 MHz) with maximum baselines of 1.5 km, yielding a resolution of ∼ 30″ and r.m.s. noise per map of 0.2 mJy Beam−1 for both of the galaxies. The Hα + N[II] images for both of the galaxies were obtained with the CTIO 1.5 m telescope.

We studied the ringed RSab(r)-type spiral NGC 4736, which has a probably slightly oval disk and a very small bar. We mapped the galaxy in the HI and Hα spectral lines and we obtained long-slit optical spectra. These data were modeled using a 2-D gas dynamical code. The 2-D potential used is axisymmetric in the inner and outer regions and oval (b/a=0.8) at intermediate radii only. The oval component rotates at a pattern speed of 40 km s–1 kpc–1, close to the observed value. Inner and outer rings, like those observed, form at the inner and outer Lindblad resonances, though they co-exist only during a limited time interval in the simulations. The morphology and kinematics of the inner ring and spiral structure as observed in neutral and ionized hydrogen can be well understood in terms of gas dynamical simulations, given the form of the (stellar) potential. What remains to be explained is the origin of the nonaxisymmetric features in the mass distribution defining the potential.

We studied a statistically complete sample of 57 southern socalled extreme IRAS galaxies, i.e., objects with a high far-infrared/blue luminosity ratio, LFIR/LB>3, using optical (imaging and spectra), radio continuum, and CO(1–0) line observations. The sample can be divided into three distinct categories: dwarfs (20%), barred spirals (35%), and interacting systems (35%). The barred galaxies are generally morphologically undisturbed, isolated systems, with average star formation rates (4 M⊙ yr–1) and efficiencies (LFIR/MH2 = 16 L⊙/M⊙) for galaxies in our sample. An enhanced massive star formation rate is the cause of the infrared brightness in 93% of all galaxies in the sample. The nuclear region is the most important star formation locus, generally unresolved at 1" resolution, i.e., less than 0.2-0.6 kpc size (H0=75 km s–1 Mpc–1), though 2 kpc size in three cases. In about two-thirds of the extreme IRAS SB’s, fainter, diffuse (2.5-10 kpc size) massive star formation is seen in the bar as well.

I review the various mechanisms for creating bars in rotating stellar disks, and conclude that the swing-amplified feed-back loop, which produces rapidly tumbling bars, remains the most probable. The bar continues to evolve after its formation in a number of ways; here I discuss what appears to be inevitable thickening normal to the plane, continued spiral activity in the outer disk and also underscore the increasingly important problem presented by angular momentum loss to the halo. Finally, I examine possible means, excluding interaction, by which bars in galaxies could be destroyed.

Recent observational constraints restrict the strict applicability of stellar dynamics in spirals to a few rotation periods. However, stellar dynamics concepts such as periodic orbits are invaluable for understanding the various dynamical processes occurring during much more periods. A distinction of two instability types in stellar systems is pointed out, the first one being well illustrated by the bar instability, and the second one by the bar bending instability. In bars the third dimension brings essential dynamical effects which modify the views about the history of bulges and the spiral secular evolution. Bars may grow, bend, thicken, and dissolve into spheroidal bulges, and spirals may evolve along the Hubble sequence in the sense Sd→Sa. This leads to a much more dynamical picture of isolated galaxies than imagined before.