A rotating gas disk was discovered around a T-Tauri star, GG-Tau, in Taurus by using the Nobeyama Millimeter Array (NMA) (Kawabe et al. 1993). To analyze the observed data, we have numerically calculated velocity profiles of CO emitted from protoplanetary gas disks by taking account of the line radiative transfer.

Recent observations reveal the velocity structure of star forming regions and the magnetic field in molecular clouds. It is known from observations that the molecular clouds rotate. It is suggested that the magnetic field have a important roll of the star formation process (e.g. Myers and Goodman 1988) and rotation of cloud have effects for evolution of molecular cloud. However it is not cleared how the magnetic field plays a roll of the star formation process in a rotating cloud.

In the previous theoretical studies, most of simulations are performed for collapse process of a rotating cloud without magnetic field (e.g. Miyama et al. 1984, Boss 1990) or collapse process of a magnetized cloud without rotation (e.g. Scott and Black 1980). Dorfi (1982) studied collapse of a magnetized, rotating cloud. However he did not calculate those with high resolutions, since he performed 3-dimensional calculations of about 6000 grid points.

Since observation instruments have been developed, it is possible to observe the star forming regions with good resolution. We study the collapse of the rotating, magnetized, isothermal cloud by mean of the axisymmetric numerical simulations with high resolution.

High resolution interferometric CO maps of the circumnuclear regions of several barred galaxies show intense CO emission arising from twin peaks, which are oriented perpendicular to the large-scale stellar bars and located where dust lanes intersect nuclear rings of HII regions. These twin gas concentrations can be explained by the crowding of gas streamlines near stellar inner Lindblad resonances. In the barred nuclear starburst galaxy NGC 3504, a large concentration of molecular gas is centered on the nucleus, apparently inside an inner Lindblad resonance. Star formation is consuming the gas most rapidly where the rotation curve is nearly solid body, suggesting that tidal shear helps control the rate of star formation. A comparison with M82 and NGC 1068 suggests that the starburst in NGC 3504 is in an early phase of its evolution, and that starburst evolution is strongly influenced by shear.

To investigate the relation between a large-scale stellar bar and circumnuclear starburst, the CO (J=1→0) emission of circumnuclear regions of three starburst galaxies NGC2782, NGC3504, and M83 (NGC5236) have been mapped with the Nobeyama Millimeter Array. The high resolution CO (J=1→0) images indicate that the molecular gas in the three starburst galaxies is located interior to the innermost ends of the paired straight dust lanes. The molecular gas at the small radii is associated with their circumnuclear starburst sites which are indicated by radio continuum emission.

We present aperture synthesis maps of the CO J=2-1 emission in the central region of the spiral galaxy IC 342. The 4” resolution maps reveal emission that is a factor of two brighter than the CO (1-0) emission mapped at the same resolution. Since the CO (2-1) emission is likely to be optically thick, the high ratio is probably due to the fact that the two transitions sample different cloud layers in externally heated clouds. The high signal to noise of the maps indicates that CO (2-1) will be a powerful tool in the study of gas in galaxies.

We discuss the use of seeing-limited near-IR spectroscopic imaging combined with high resolution millimeter and submillimeter wave observations, as a diagnostic in the study of the nuclear interstellar medium in starburst galaxies and active galactic nuclei. As an example, recent near-IR spectroscopic imaging of the starburst galaxy NGC 253 is analyzed. It is shown that the central ~ 100 pc of NGC 253 contains a number of giant star forming complexes, the stellar content of which is at least as large as that of the 30 Dor region in the LMC. We suggest the use of the [FeII]/Brγ ratio as an approximate age indicator for such complexes. The warm component of the nuclear molecular medium in NGC 253 detected in submillimeter CO spectra and in near-IR rovibrational lines of H2 is probably heated by stellar UV radiation or slow shocks in star forming regions, rather than by supernova remnant shocks. There are indications that molecular material is being removed from the nuclear region by the “superwind” observed in optical emission lines.

Approximately thirty of the luminous infrared galaxies highlighted by the IRAS survey have now been mapped at high resolution using the millimeter arrays. In virtually all cases, extremely high gas concentrations are found in their nuclei (≤2 kpc) and in several cases, the gas mass fraction is extremely high (25-100%). Optical and near infrared imaging of the most luminous infrared galaxies shows significant distortions, double nuclei, and/or tidal tails indicating that these galaxies have probably undergone a recent galactic interaction. The dense molecular gas probably plays a pivotal role in the evolution of such dynamically disturbed systems: being dissipative the gas readily sinks to the central regions where it may fuel a nuclear starburst and possibly build up and fuel a central active galactic nucleus. In this picture, the IRAS galaxies may be crudely characterized by three parameters: the initial mass of ISM in the progenitor galaxies, the time since the interaction, and the fraction of the total luminosity attributed to young stars versus an active nucleus. In this scenario, systems such as the antennae (NGC 4038/39) may represent the early stages of a merger before the gas has been deposited in the nucleus; Arp 220 the phase in which a large nuclear gas concentration is presently fueling a starburst/AGN, and NGC 1068 the later phase in which much of the central gas concentration has been consumed and the residual gas exists in a circumnuclear ring or arms.

Recent millimeter-wave observations of CO from the protogalaxy candidate IRAS F10214+4724 with single dishes and interferometers indicated that the huge amount of molecular gas is associated with the high-z galaxy with huge infrared luminosity. An overview of the results of recent observations of IRAS F10214 +4724 is shown. The implications of the results based on aperture synthesis CO observations and origin of the huge infrared luminosity (starburst or dust- enshrouded QSO) are discussed by comparing them with the “nearby” ultraluminous IRAS Galaxies.

Preliminary observations of the z = 2.286 protogalaxy in the redshifted J = 3 − 2 transition of CO made with the Owens Valley Radio Observatory array suggest that the CO emission is spatially extended. This is particularly evident in the narrow band spectral channels. There are indications of CO emission regions in the field of IRAS F10214+4724 that are not related to the IRAS galaxy.

The IRAM interferometer has been used to image the distribution and kinematics of the HCO+ line in the nuclear region of IC 342 and of the HCN line in the nuclear region of Maffei2. Both regions were also imaged in the continuum at 3mm. These observations are compared with observations of HCN in IC 342 and CO in both galaxies.

IC 342 is a large nearby (1.8Mpc) spiral galaxy undergoing a moderate nuclear starburst. Previous maps of the inner arc minute in 13CO (1→0) show that the nuclear molecular gas forms spiral arms approximately 500 pc in extent in a density wave pattern (Turner & Hurt, 1992).

M83 is the best sample to investigate gas response to bar potential because it is one of the nearest galaxy with a pronounced bar structure (distance=3.7 Mpc). Handa et al. (1990) observed it with the Nobeyama 45-m telescope in CO(J=1-0) and found concentration of the CO emission to the dust lanes along the bar and non-circular rotation. However we need better spatial resolution in order to investigate kinematics and distribution of molecular gas in the nuclear region. So we observe the central region of M83 using the Nobeyama Millimeter Array. The synthesized beamsize was 12″ × 6″ and frequency coverage was 325 km s-1.

All the existing molecular maps of M82 made up to now have revealed a double-lobed stucture interpreted as a uniform torus (Nakai et al. 1987). We have observed the central part of M 82 in the HCN (J=1−0) line with the Plateau de Bure IRAM interferometer (spatial resolution = 2.5″). The HCN molecule, due to its high dipole moment, traces clumps with a density of about 105 cm−3. For technical reasons we have divided our study in two fields. We present here the results obtained in the south-west field, covering one lobe of the “molecular ring” and the center of the galaxy in the velocity range 0-260 km s−1.

Dense gas in molecular cloud cores is essential in researches of extragalactic star formation (e.g. Solomon, Downes, and Radford). To determine the physical relations between star-forming regions and dense gas, we have observed CS (J=3→2) in starburst galaxies M 82 and NGC253. The J = 3 level of CS is 14.1 K and the critical density for excitation is 4 × 105 cm−3.

NGC 660 is a gas-rich, peculiar polar ring RSBa-type starburst galaxy with two distinct morphological and kinematic components: an inner disc, seen almost edge-on, with a major axis position angle of 45° and a diameter of ~11 kpc [D=13 Mpc, Ho=75 kms−1 Mpc−1], and an outer polar ring (p.a. 170°) with a diameter of 31 kpc, inclined on average about 55° with respect to the major axis of the inner disc.

We obtained deep, 30 min. exposure CCD images of NGC 660 with the 105 cm Schmidt telescope of Kiso Observatory in the B, V, R, and I bands. A preliminary reduction shows that the inner disc is clearly redder than the polar ring and the nucleus.

Optical spectra indicate that the galaxy has a LINER-type spectrum, suggesting intense massive star formation in the nucleus. We obtained a long-slit Ha spectrum along the major axis of the inner disc at ESO, which shows a very steep gradient near the nucleus. Assuming an inclination of 80°, it implies a rotational velocity of about 150 km s−1 for the inner disc.

Knowledge of the distribution and excitation of gas close to the nuclei of starburst galaxies is an essential element in the construction of models dealing with intense, but short-lived, star forming events. Building a comprehensive picture of the concentrations of various gaseous components in such regions calls for a multi-wavelength approach: the principal cooling lines of cold (T≤200K) molecular gas fall in the millimetre waveband, those of hot (T~1−3×103K) excited molecular material in the near-IR, and those pinpointing starburst activity in the optical. In many cases the extents of the emitting regions are on the order of only a few arcseconds.

As part of such a study into the relationship between various near- and circum- nuclear gaseous components in starburst galaxies, we have obtained data on NGC 6764, a barred spiral classified as a LINER, at resolutions of 1″−4″ across the optical, near-infrared and millimetre wavelength regimes. In a previous paper (Eckart et al. 1991) we discussed extensive single dish millimetre and JHK near-IR measurements of the nucleus and disk of NGC 6764. Here we present new near-IR observations obtained with the MPE FAST instrument (Rotaciuc et al. 1991) at the William Herschel Telescope, along with 2″ resolution 12CO J=1-0 (115 GHz) interferometry measured with the Nobeyama millimeter array and 1″ optical spectroscopy from the 3.5m Calar Alto telescope.

Starburst regions are frequently located in galactic central regions and CO observations indicate that these regions contain a large amount of molecular gas (e.g. Lo et al. 1987). However, the triggering mechanism for starbursts and the mechanism of the high mass supply rate of gas into a galactic center are still unclear.

It is suggested that tidal encounters of galaxies remove angular momentum of gas and trigger rapid gas accretion and starburst. Noguchi(1988) has shown by computer simulations that galaxy-galaxy interactions induce a stellar bar, and gas loses its angular momentum and accumulates to a galactic center. In his numerical simulation, non-axisymmetric potential of a stellar bar plays an important role in the accretion of gas. However, it is not obvious whether or not gas accretes into a nuclear region within a few hundred pc only by the effects of stellar bar.

Wada and Habe (1992) investigated the dynamics of self-gravitating gas in a barred potential by 2-D numerical simulation, and show that even if the bar is weak, for the initial gas mass ratio to stellar mass grater than 10%, a central elongated gas ring formed at near ILRs becomes unstable and collapses. As a result, a large amount of gas can be supplied to galactic center. They conclude that both the effect of the self-gravity of the gas and the existence of ILRs are necessary to the rapid gas fueling in a weak barred potential.

Recently, it has been shown that some of nearby spiral galaxies have very massive (107-8Mʘ) and large (several 100 pc - ~ 1 kpc) molecular gas clouds (M51: Rand & Kulkarni 1990; NGC1068: Planesas et al. 1991). Since these clouds are significantly more massive and larger than those of so-called Giant Molecular Clouds (GMCs) found in our Galaxy, they are called Molecular Super-clouds (Rand & Kulkarni 1990; hereafter MSCs). In order to study observational properties of MSCs, we present the results of high-resolution (4”) 12CO(J=1-0) mosaic mapping of central 2.’5 region of the Sbc galaxy M51 using the Nobeyama Millimeter Array (NMA). Our main results are summarized in the followings (Tosaki, Kawabe & Taniguchi 1992).

In our Galaxy, molecular gas forms clouds with masses of ~ 105M© and with sizes of several 10 pc, which are called Giant Molecular Clouds (Sanders 1985; hereafter GMCs). Such GMCs are also observed in nearby spiral galaxies M31 and M33 (Lada et al. 1988; Wilson & Scoville 1990). On the other hand, one of the well-studied spiral galaxy M51 has more massive and larger molecular clouds. Since their typical mass and size are 107-8MQ and several 100 pc, respectively, they are called Molecular Superclouds (Rand & Kulkarni 1990; Tosaki et al. 1992; hereafter, MSCs). A question arises as what causes the difference in structural properties of molecular gas among the spiral galaxies. In order to answer this question, we should make higher resolution studies both spatially and spectroscopically. In this paper, we present the results of high spectral-resolution study of the MSCs in M51 based on the 12CO (J = 1 − 0) mapping made with the Nobeyama Millimeter Array (Tosaki et al. 1992). The spatial resolution is 5.”3×4.”9 corresponding to 240 × 230 pc at distance of 9.6 Mpc. The spectral resolution is 3.25 km s−1. The analysis is made for the 1’ region whose center is offset 42” south and 7” east from the nucleus, because a very intense molecular arm is present in this region. Our Main results and conclusions are as follows.

NMA 12CO(J=1-0) observations of the radio lobe spiral galaxy, NGC 3079, reveal a dense, rigidly rotating ring of molecular gas with a radius of about 750 pc. In addition, a tilted CO component as well as several molecular gas “spurs” are interpreted as linear features which are accelerated outwards by the nuclear outflow.