B – V and R – I color maps (from CCD imagery obtained at Cerro Tololo Inter-American Observatory) of six barred spiral galaxies have been used (Horst 1992) to investigate stellar populations within the bars and nuclei. Two-color diagrams show that the distribution of pixel colors largely parallels the expected locus for normal unreddened stars. If the “reddening” law is assumed to remain fairly constant, and if the slope of the vector associated with this reddening law is additionally assumed to be commensurate with that derived from models which take into account both absorption and scattering (Witt et al. 1992), one concludes that the overall effects of internal extinction are remarkably uniform along the bars and within the nuclei of all six galaxies. It thus appears reasonable as a first approximation to shift the observed data along the assumed reddening vector to estimate the spectral types of stars that are present and to investigate differences between bar and bulge populations. Nevertheless, to correct surface brightness distributions for the effects of internal extinction, and hence to proceed with more detailed attempts to model the various luminosity components (i. e., the bulge, bar, etc.), is a complex problem which must be addressed through numerical models explicitly designed to reproduced barred systems.

The fact that a galaxy is barred may have an effect on the source of the far-infrared (FIR) radiation observed. Yet, to date, no one has addressed the effects that that might have on interpreting the global FIR signal. We hope to add to the existing data on FIR radiation in galactic bulges by comparing a barred galaxy, M83, to an unbarred galaxy, M74.

We use optical, Ha and UV images that are blurred to the same resolution as the IRAS HIRES images. Looking at the blurred UV images, bright "globs" were chosen and apertures were fit to them. The “globs” were then located on the optical, Hα and FIR images and fluxes were determined for each aperture used.

Star formation along the bar is common in late-type barred galaxies (Phillips and Garcia-Barreto et al., these proceedings), which tend to have weak stellar bars. It is rarer in strongly barred galaxies, e.g., early-type spiral galaxies. Abundance gradient measurements (Martin & Roy 1995) and simulations (Friedli & Benz 1995) suggest that star formation along the bar of strongly barred galaxies may indicate a young bar. Since bars can be created in tidal interactions and mergers (Noguchi 1987), it is of interest to investigate the star formation properties of barred galaxies in different environments. We use Hα images to compare the star formation properties in the bar region of a sample of barred galaxies in the Virgo Cluster and a control sample of isolated galaxies. We focus on the three galaxies with the strongest star formation along the bar, including NGC 4424, a possible merger remnant.

Images: 1.5m Spanish telescope in Calar Alto, Thomson blue coated 1024×1024 CCD, 0.31″pixel−1. Exposition times of 1800, 1500 and 1200 (BV R) and 2000 seconds (Hα and continuum) were used. Seeing FWHM = 1″. Spectra for NGC 6701: 3.5m telescope, PA=25°, 115°, 145° and 175° (Hβ region), 2.2m telescope, PA=25° and 115° (Hα region). The spectrum along the companion galaxy (PA=0°) was also obtained with the 2.2m telescope.

In Figure 1a the bar is clearly seen, extending almost all along an axis very close to the disk minor axis. The spiral arms emerge from the bar, with the arm to the north being the more luminous one. The main spiral structure delineates a pseudo-outer ring when the arms close together. The prominent bar structure has a diamond-like aspect (22″×l2″) mainly traced by the two more intense sides. The zones just immediately inside these linear paths are notably fainter, as expected for a region in which the presence of dust is important. The ellipse fitting to the µB=23.5 mag arcsec−2 isophote gives a = 13, b = 12 and PA = 25°. Total (corrected) magnitudes are mB = 12.96(12.65), mV=12.44(12.20) and mI=11.64(11.46).

Imaging spectrophotometry in the main nebular lines has been performed on 65 H ɪɪ regions in the ringed galaxy NGC 4736. O/H abundances were derived using the line ratios [O ɪɪɪ]/Hβ and [N ɪɪ]/[O ɪɪɪ] calibrated by Edmunds & Pagel (1984). We show that the O/H scatter in the resonance ring of star forming regions is small, no greater than normally expected in the well-mixed ISM of disks of gas-rich galaxies. The global O/H gradient (−0.046 dex/kpc) in the disk of NGC 4736 is shallower than gradients of normal spirals but comparable to gradients observed in weakly barred spirals. This last result could indicate that radial mixing is or was present in NGC 4736. The oval distortion in the central regions can be responsible for this homogenization but it is also possible that a strong bar was present in the past.

We present new high quality Ha continuum-subtracted images of the grand design galaxies NGC 157, NGC 3631, NGC 6764, and NGC 6951, two of them barred and two non-barred, and describe the statistical properties of the HII regions. We have determined the positions, angular sizes and fluxes of individual HII regions, and construct luminosity functions and diameter and density distributions. We find no significant differences between arm and interarm HII region properties, or between the barred and non-barred galaxies. This paper summarizes work described in more detail by Rozas et al. (1995a,b)

The Hα brightness distribution of a face-on galaxy is a classical representation of the massive star formation rate per unit surface area. Here, we present a test for the degree of symmetry in this distribution, aimed at deciding whether this parameter shows a significant difference between barred and non-barred galaxies. The test consists in deriving the cross-correlation function of the Hα brightness as a function of curvilinear distance along pairs of opposed arms. In order to use the test, we first apply a geometrical unfolding technique. Here we explain this technique, and present the initial results of applying the test to NGC 157 and NGC 6764.

We present a brief report on the B, V, R, I, and Hα CCD surface photometry of the southern SABab galaxy IC 4214. We obtained isophote maps, luminosity profiles, and basic geometric and photometric parameters in BV RI, and mapped the distribution of the gas through continuum subtracted Hα emission line images.

We present surface photometry in U BV RI passbands of the barred spiral galaxies NGC 7479 and NGC 7606, for which observations were obtained at the Cassegrain focus of the 2.5-m Isaac Newton Telescope at La Palma. Data are presented in the form of images and mean radial profiles from azimuthal fits of ellipses, giving the luminosity, ellipticities and position angles of the isophotes as functions of the galactocentric radii. Images in I-band are shown in Figure 1 of NGC 7479 (left) and NGC 7606 (right). These belong to a sample of galaxies with moderate circumnuclear starbursts. We are analyzing their structure to study the effects of departures from an axisymmetric potential for the dynamics of a galaxy. One objective of this study is to make a three-dimensional model of the bar and bulge using the method of photometric inversion. The sample consists of 27 spiral galaxies with and without a bar.

We present the results of a VLA D-configuration survey of a sample of Barred Magellanic type (SBm/IBm) galaxies. The data show that: (1) the HI is extended well beyond the optical diameter; (2) the HI distribution often has a different position angle than the optical distribution; (3) the bar morphology is typically manifested in the HI kinematics; (4) these galaxies not only tend to have gaseous companions, but they also tend to be strongly interacting systems; and (5) the companions have no obvious optical counterparts.

Given that dust and molecular gas tend to concentrate at the locations of either shocks or orbit crowding, the study of the dust morphology of barred spirals can give insight into the kinematics of the galaxies. In order to do this, we present a sample of barred galaxies for which we have obtained near infrared and optical photometry and BIMA interferometer observations of CO emission. We obtain the dust extinction and relative scale height of the dust and stars using a radiative transfer model to interpret the photometry. We find that the scale height of the stars compared to the dust is generally larger in the central regions compared to further out in the bar dust lanes. The morphology of the dust extinction regions closely resembles the distribution of CO emission. An analysis of a larger sample of galaxies with IR data indicates that dust column densities appear larger in the nuclear regions than in the bar dust lanes. The sample also shows that the distribution of dust is not symmetrical along the bar with one side of the bar usually having a larger column density of dust than the other side.

A general overview is presented of the global gas kinematics of barred spirals, using HI and Hα data. The question of dark matter in barred spirals is also discussed.

Images of molecular gas in spiral galaxies show two types of bar structure: large-scale bars, which are correlated with the presence of stellar bars, and generally follow the spiral structure, and nuclear “bars” of a few hundred parsecs in size, which show no direct correlation with the presence of a stellar bar. The dynamical origin of nuclear molecular bars is unclear, although they are consistent with radial inflow of gas into the nucleus, and subsequent evolution of the gas structure.

The morphology and kinematics of molecular gas in the central regions of barred galaxies are described. The largest gas concentrations are often located near ILRs, although there is a range of morphologies. The gas motions associated with star-forming rings are predominantly circular, while motions just beyond the rings are often non-circular and in some cases show clear radial inflow. In barred galaxies with circumnuclear starbursts in early phases of evolution, the CO is centrally peaked, perhaps inside IILRs. The most intense star formation occurs where the gas motions are circular, and where the rotation curve rises steeply and is nearly solid body.

We have mapped the distribution and kinematics of H ɪ in NGC 1433 and NGC 6300 with the Australia Telescope Compact Array, in order to test the association between resonances and ring phenomena. We find a bar pattern speed in NGC 1433 of Ωp = 26 ± 5 km s kpc−1, and postulate that NGC 6300 is still evolving to a mature resonance-ring galaxy.

Integral Field Spectrograph observations of southeast (SE) gas outflow in the center (11×13 arcsec) of NGC 4258 with spatial sampling 0.6 and 1.2 arcsec were made with the 6-m Telescope. Reconstructed spatial and kinematic structure of the SE outflow from 20-30 pc to 200-220 pc are presented.

We have made high resolution HI observations using the VLA1 of the barred spiral galaxy NGC 1365. This galaxy contains 15.2 × 109M⊙ of HI. The velocity field is strongly affected by the bar only in the inner parts. NGC 1365 has a warp and it has 4 well developed spiral arms and 2 rudimentary ones. NGC 1365 has an unusually dropping rotation curve.

H ɪ absorption measurements against strong continuum background sources are an excellent tool to study the cold ISM in the line of sight to the object (e.g. pulsars, galaxies, quasars). Here we present a brief overview of such studies against the nuclear region of starburst galaxies. The high angular resolution provided by synthesis telescopes allows us to resolve the central region of nearby galaxies and thus investigate the gas kinematics close to the nucleus. The detection of fast-rotating nuclear rings is related to the bars in these galaxies which in turn might have been triggered by tidal galaxy-galaxy interactions.

It has been suggested that the peanut-shaped bulges seen in some edge-on disk galaxies are produced when bars in these galaxies buckle. This paper reviews the modelling which seeks to show how bars buckle, and I present a very simple new model which captures the essential physics of this process. I then discuss the problems in establishing observationally the connection between peanut-shaped bulges and bars. Confirmation of the link has proved difficult because boxy bulges are only apparent in edge-on galaxies whereas bars are only easily detectable in more face-on systems. Finally, I present a new technique which avoids this difficulty by searching for the distinctive kinematic signature of an edgeon bar; application of this method to spectra of peanut-shaped bulges reveals that they are, indeed, associated with hidden bars.

Theoretical studies suggest that large-scale stellar bars can be highly effective in delivering gas to the central few hundred parsecs of a spiral galaxy, which may then initiate rapid star formation. Further instabilities may lead to additional inflow to physical scales relevant for active galactic nuclei. We test these predictions in light of recent observations. Compared to unbarred spirals, barred galaxies of type S0-Sbc have a higher probability of exhibiting nuclear star formation, as well as a higher formation rate of massive stars; neither effect is present in spirals of later morphological type. Bars, on the other hand, do not have an obvious influence on active nuclei. We discuss the implications of these findings for the fueling of central star formation and active nuclei.