The last decade has brought about a completely different picture of elliptical galaxies. The once considered completely inert systems have revealed the presence of fair amount of dust, cool and cold gas, and undergoing star formation. The current statistics is that 80% of elliptical galaxies have detectable cool gas components, and as many as 60% have ionized gas (Knapp et al. 1989, Goudfrooij et al. 1994). Several single-dish CO surveys have been reported in the literature, allowing the deduction of several general properties of the molecular gas in early-type galaxies (Sage & Wrobel 1989, Lees et al. 1991, Wiklind et al. 1995).

We have made CO mapping observations of nearby barred spiral galaxies (NGC253, NGC3504, NGC4303, NGC4321, NGC6951, M83) with the Nobeyama 45-m telescope using the 2×2 SIS focal-plane array receiver. The purpose of this project is to investigate distribution and kinematics of molecular gas in barred spiral galaxies and the relation between star formation and them. We present some of the results (NGC3504 and NGC6951).

Our survey observation is high spatial resolution (16″) by NRO observatory 45 m antenna and have many galaxies of sample. This high resolution observations (16″ = 1.6 kpc at 20 Mpc) could be to resolve the some characteristic structure, typical molecular gas disk, arm - interarm and optical bar.

To understand the origin and evolution of starburst activity, we must study the full evolution of starburst; i.e., pre-, on-going, and post-starburst phases. It seems reasonable to suppose the numerous A-type stars indicate past starburst and they show strong Balmer absorption. NGC7331, nearby early-type spiral galaxy, is one of the poststarburst galaxies which show strong Balmer absorption. The optical spectra of NGC7331 were dominated by component of intermediate-age (5 × 109 years) stellar populations (Ohyama & Taniguchi 1996). We present the result of the high resolution CO observations of NGC7331 using Nobeyama Milimeter Array.

M51, the Whirlpool Galaxy, at a distance of ≈ 9,6 Mpc and a systemic velocity of 465 km s−1, is the closest “Grand Design” spiral galaxy. Its low inclination (20°) makes it an excellent target for structural studies, e.g. the formation of arms in response to a spiral density wave causing gas streaming motions. We have obtained a high resolution, sensitive map of the inner 2.5′ of M51 using the Caltech six-element OVRO array. The map consists of a 19-field mosaic, taken using three different telescope configurations. The resolution is 2.5″, (corresponding to 115 pc linear size) and 3.5” for the robustly and naturally weigthed maps, respectively.

Bars are considered to be an important fueling mechanism for nuclear starburst activity, and are believed to be a dynamical result of gravitational interactions and merging. Furthermore, in a recent study, Das & Jog (1995) suggest that the dynamical impact of a bar will also have important consequences for cloud properties in the bar and nucleus. NGC 7479 is a barred galaxy with an unusually long and strong bar. At a distance of D=32 Mpc the bar length is ≈10 kpc. We selected NGC 7479 for a study of cloud properties in bars because of its proximity and because molecular gas is distributed along the whole length of the bar (e.g. Quillen et al. 1995).

Elliptical galaxies are traditionally defined as gas–free, inert stellar systems. Observations of continuum emission in the far–infrared (FIR) and sub–mm wavelength bands have, however, shown that a large fraction of all ellipticals, ~50% (Jura et al. 1987), contain a dust component. The infrared emission is due to warm dust, in many cases associated with star formation and/or weak AGN activity, while cold dust dominates the long wavelength continuum emission (e.g. Wiklind & Henkel 1995). Some elliptical galaxies also contain a molecular gas component, as seen through CO emission (Lees et al. 1991; Wiklind et al. 1995; Knapp & Rupen 1996). The dust and molecular gas are believed to be associated with each other, but it is not clear what powers the emission: star formation activity and/or AGN activity. Both the molecular gas mass and the FIR luminosity are on average lower in ellipticals than in spiral galaxies of similar luminosities. However, the LFIR/MH2 ratio is larger for the elliptical galaxies. If this ratio is a measure of the star formation efficiency, this suggests that gas is being used up more efficiently in elliptical galaxies than in normal spirals (e.g. Wiklind et al. 1995). Other possibilities is that the FIR dust emission is not only powered by UV–light from young stars, but from other sources as well, or that some dust is not spatially associated with the molecular gas.

Our Galaxy is representative of the majority of spiral galaxies, which are highly non-axisymmetric, developping bars (m = 2 perturbations), but also lopsidedness and off-centering (m = 1), and superposed higher order perturbations. Recent high-resolution N-body and gas-dynamical simulations have considerably improved our knowledge on the nature and formation of these features. Contrary to previous beliefs, they are not long-lived, but fade away and can be reformed continuously, provided enough gas is supplied to the center, to maintain gravitational instability. The dynamical mechanisms involved are reviewed and discussed, and in particular the new features brought by the dissipative gas component. The role of these axisymmetries in the galaxy evolution, mass concentration, together with nucleus fueling are described, and typical time-scales discussed in particular for confrontation to the Milky Way observations.

Starburst phenomena in interacting and merging galaxies have been one of the most widely investigated subjects in today's galactic astronomy. On the theoretical side, a large body of numerical studies have been performed in order to interpret available observational data. Numerical simulations have been advanced to the point where they can include interstellar medium (ISM) and star formation process.

One of our nearest neighbors is a large spiral galaxy with abundant molecular gas in its nucleus. IC 342, a face-on Scd galaxy at a distance of 1.8 Mpc, is close enough to give us a view of individual molecular clouds with millimeter interferometry. The CO distribution in the nucleus of IC 342 consists of two very open spiral arms (Lo et al. 1984; Ishizuki et al. 1990) that continue to within 50 pc of the dynamical center (Turner & Hurt 1992). The total extent of the nuclear “mini-spiral” is ~ 500 pc. Corresponding arms are observed in Hα (J.S. Young, private comm.). However, the Hα arms are systematically offset by 50-100 pc from the CO arms (Turner & Hurt 1992). The offset of the Hα arms to the outer, leading edge of the CO arms is consistent with a picture of density wave-induced star formation in the arms (Turner & Hurt 1992). Energy dissipation and angular momentum transfer in spiral arms is believed to drive a slow drift of gas inward; if this is the case, the molecular “mini-spiral” in IC 342 is short-lived, and will probably no longer exist in another 108 years.

Although numerous gaseous bars are observed, they seem to be much less common than stellar bars. This might be due to an observational bias, but gaseous bars could also be difficult to form and/or have short lifetimes. Gas morphology is strongly dependent on the resolution and the considered scale. A true bar-like shape (Maffei 2) should not be confused with either ring-like plus open arms (IC 342), or “twin peaks” (NGC 3351) morphologies. Typical observed gaseous bar characteristics are 2ag ~ 1 kpc, and Mg ~ 0.1–0.3Mdyn inside a few 100 pc. Below, three mechanisms of gaseous bar formation, as well as their evolution, are briefly discussed.

Numerical modeling of the interstellar gas in galaxies is an effective approach to infer galactic gravitational structure. This is because the dynamical behavior of gas is very sensitive to the background gravitational potential. Since the dynamical resonances depend closely on the mass distribution and the pattern speed of the non-axisymmetric component, it is possible to determine these dynamical parameters by comparison of numerical simulations and gas observations.

The inner Galaxy light distribution recovered non-parametrically from the COBE/DIRBE surface brightness data shows an elongated bulge set in a highly non-axisymmetric disk. Gas flows computed in the potential of the COBE bar/bulge and disk have been compared with HI and CO line observations. For the best values of the NIR mass-to-light ratio and pattern speed a good match to the tangent point locations of the inner Galactic spiral arms is obtained.

Bars in galaxies are frequently found to be off-centered, so that the center of the bar does not coincide with the center of rotation, with a difference which typically amounts to several tens of parsecs. This is clearly seen in the distribution of the gas and the rotation curves at the center of the Milky Way, and in nearby barred galaxies (Blitz, these proceedings, and del Burgo et al., these proceedings).

The nuclear region of the supergiant barred spiral galaxy NGC 1365 contains bright “hot spots”, as seen at optical wavelengths, as well as a number of non-thermal radio continuum sources, some of which remain unresolved at 0.25” × 0.10” resolution (Sandqvist et al. 1995, A&A 295, 585).

The distribution of [OIII] λ5007 emission from the nuclear region supports the scenario of an [OIII] cone emanating from the Seyfert nucleus. The velocity field of the high excitation gas in the cone has been modeled by Hjelm & Lindblad (1996, A&A 305, 727) in terms of an accelerated bipolar conical outflow. Such conical or biconical high-excitation emission-line structures extending from the position of the nucleus are found in several active galactic nuclei.

We propose a new picture accounting for the dominant features in the observed ℓ−V distribution of the Milky Way gas within the central few kpcs, based on the gas flow in two self-consistent and symmetry-free barred dynamical models. These models are snapshots selected from high resolution 3D N-body and SPH simulations with 4 × 106 stellar and dark particles and 1.5 × 105 gas particles, and with initial conditions adapted from Fux (1997). The main results are shown in figure 1. In both models, the inclination angle of the bar relative to the Sun-Galactic centre line is 25°, the corotation radius close to 4.4 kpc and the sound speed of the gas 10 km s−1.

NGC 5383 is a barred galaxy of type (R′)SB(rs)b: pec with well developed dust lanes which provide valuable information about the dynamics of the galaxy. It is well known that dust lanes in barred spiral galaxies represent the loci of shock fronts which are caused by the gas inflow driven by bar potential (Athanassoula 1992). However, detailed morphology of dust lanes depends on the distribution of masses in bulge, disk, and bar as well as bar pattern speed. We conducted a UBVRI and Hα surface photometry and SPH simulations for NGC 5383 to investigate the relation between the morphology of dust lanes and the dynamical properties of barred galaxies.

1. — Many galaxies are seen to be undergoing a range of activity associated with an active nucleus. Whilst much effort goes into understanding the mechanisms involved, very few authors have considered how such AGNs might form.

2. — Our group has for many years being studying the formation of galaxies based on the collapse and fragmentation of self-gravitating gas dynamics (e.g. Williams, 1997).

3. — However, to produce jets (which we are using as a tracer of AGN activity) requires additional physics. Other work (e.g. Matsumoto et al., 1996) has shown that magnetic fields are important in the production of jets from accretion discs.

4. — Hence we have produced a fully self-gravitating, magnetohydrodynamic code with the aim of studying the formation of an AGN starting from the initial collapse of a primordial overdensity.

Microlensing (μ—lensing) towards the bulge started out as a unique technique of detecting dark objects in the Galactic disc (brown dwarfs) by measuring a rare transient brightening of one star among millions of stars in the Galactic bulge (Paczyński 1991). More than 200 events have been detected towards the Bulge since 1993 by the DUO, MACHO, OGLE etc. survey teams. But where are the lenses? Are they truly dark objects or merely faint stars? I show the results on the mass function, spatial distribution and dynamics of these observed lenses based on a dynamical model of the Galactic bar.

As the observations of highly flattened galaxies including the Milky Way and many-body (N-body) simulations show, the central parts of these systems, say, at distances r < 0.5–0.7 kpc from the center, rotate slowly and their local circular velocities of regular rotation become less than (or comparable to) the residual (random) velocities. In such a thin, practically nonrotating circumnuclear disk, a typical star moves along the bending, perpendicular to the equatorial plane layer under the action of two forces which act in opposite directions: the destabilizing centrifugal force Fc and the restoring gravitational attraction Fg. Obviously, fierce instabilities of the buckling kind developing perpendicular to the plane may not be avoided if Fc > Fg. The latter condition is none other than the condition of “firehose” electromagnetic instability in collisionless plasmas which is driven by the particle “pressure” anisotropy.