Recently, as a solid physical mechanism which links circumnuclear starbursts to AGN fueling, Umemura, Fukue, & Mineshige (1997a) have proposed a radiative avalanche which is the black hole accretion driven by intensive radiation from circumnuclear starbursts of ≲ 100 pc.

Recently, a novel mechanism for fueling active galactic nuclei (AGNs) has been proposed by Umemura et al. (1997a, b). That is a radiative avalanche, in which a rotating gas disk sheds angular momentum due to the radiation drag force exerted by starlight from circumnuclear starbursts, so that the mass accretion onto nuclei is driven. Originally, a thin ring of a starburst region has been assumed for simplicity. However, recent observations have revealed that circumnuclear starburst rings have radial extension of ∼ 10pc up to kpc, and they often consist of compact star clusters of < 10pc Thus, the ratio of the half thickness to curvature radius of the ring can be minimally less than one tenth when all the star clusters are aligned on a plane of an inner gas disk, while the ratio could be larger if the distributions of star clusters are extended due to some velocity dispersions.

In order to study relationship between molecular gas and star-forming activities, we have made observations of the barred spiral galaxy NGC 253 in 12CO(J = 1–0), 13CO(J = 1–0), and HCN(J = 1–0) emission lines with the Nobeyama 45-m radio telescope. NGC 253 is located in a distance of 2.5 M pc(Mauersbergeretal.(1996)) and has an inclination angle of 78°.5 (Pence 1980). This galaxy has a starburst nuclear region and is suggested in an early stage of a starburst (Rieke, Lebofsky, & Walker (1988)).

Continuum observation of galaxies in millimeter-wave gives informations on dust emission from molecular clouds, free-free emission from HII region and synchrotron emission from SNR and diffuse component. The free-free emission can be observed only at millimeter-wave frequencies and their emission is optically thin, it can be a good indicator of their star-formation activities.

Recently, the HST imaging observations have revealed that the central arc second region in NGC 1068 has a clumpy structure (Macchetto et al., 1994) and the HST UV imaging polarimetry has revealed the centrosymmetric pattern of the position angles of polarization (Capetti et al., 1995), which indicates that the medium in this region is actually scattering the radiation from a small source, in accordance with the unified model of active galactic nuclei (Antonucci & Miller, 1985).

Starburst activity is often heavily obscured by dust. To see through the dust and measure the full extent, power and dynamics of the starburst, we are surveying hydrogen radio recombination lines (RRLs) from famous nearby starburst galaxies. Exploiting the improved sensitivity and dynamic range of aperture synthesis arrays such as the VLA and the AT and millimeter-wave telescopes such as SEST and the IRAM-30m telescope, we have searched for RRLs in about 25 starburst galaxies. RRLs have been detected in 14 galaxies. The observations were made variously at 1.4, 4.9, 8.4, 86, 135 and 232 GHz (Anantharamaiah et al 1993, Zhao et al 1996, 1997, Phookun et al 1997). Table 1 summarizes the observations. In all the cases the detected line originates in the nuclear starburst region and the emission region is resolved with a beam of 1–3″.

Seyfert galaxies often have extended emission line regions around their nucleus. We started an observation program of optical tridimensional spectroscopy for circumnuclear regions of nearby Seyfert galaxies to investigate the ionization source of the gas of just vicinity(typically several hundred pc) of nucleus.

We present results of an optical tri-dimensional observation of the central 2′ × 12″ region of the starburst galaxy NGC 2782. The circumnuclear Hα emission lines consist of broad (δv ~ 300 km s−1), blue-shifted component and narrow (δv < 100 km s−1) component and we first revealed the two-dimensional spatial distribution of those two components. The broad Hα emitting region is extended to 6″ (> 1 kpc) south from the nucleus and the emission-line ratios indicates that shock heating may be the main excitation mechanism of the ionized gas in the region. We conclude that this region is a superbubble outflowing from the nuclear starburst region.

A series of spectral observations of the nucleus of the Seyfert galaxy NGC4151 were obtained with the TV scanner of the 6-meter telescope of SAO, Russia (Nazarova et al. 1997). The nucleus of the NGC4151 was observed repeatedly between 1986 and 1990 in the spectral range from 3900Å to 4950Å. The emission line fluxes were obtained by fitting multiple Gaussians. We parameterise the asymmetry of the HeII λ4686 and Hγ lines by the peak wavelength of the broad Gaussian fitted to the blend at ≈4686Å and at ≈4340Å. Significant changes have taken place in the asymmetry of the Hell line while there is only a gradual and small change in the asymmetry of Hγ line. However, the change in the integrated line flux is exactly opposite. It seems possible that the asymmetric variations of the broad component of Hell line and nearly stable asymmetry in the broad component of Hγ line during the period 1986-1990 might reflect the long-time variations in broad components emitted from HIL and LIL zones respectively. Work is partially supported by RBRF grant 97-02-17625.

As the closest Seyfert nucleus, NGC 1068 is a key object to establish on firm grounds the model of active galactic nuclei (AGN). Two important questions relative to AGNs are : i) can we actually see the parsec-scale torus of dust and molecular gas around the central engine predicted by the popular Unified Model model (e.g. Antonucci, 1993)?; ii) how the gas is brought down to the parsec scale to feed the monster, and, in particular, is there a micro spiral/bar system that could produce the required torque ? Adaptive Optics in the near-IR has potential advantages to make a significant progress in those two questions : the low dust opacity and the excellent angular resolution.

The radio emission from the Galactic Center is a mixture of thermal (free-free) and non-thermal (synchrotron) emissions (Fig. 1a). However, the spectral index in the central 3° region is flat almost everywhere (Sofue 1985), even in regions where strong linear polarization is detected. Therefore, a flat spectrum observed near the galactic center can no longer be taken as an indicator of thermal emission.

The kinematics and structures of the molecular clouds probably give us key information for activities in the Galactic center region. CS lines are good tracers of dense molecular clouds. In addition, the lines are expected to be nearly free from the strong contamination of disk molecular clouds because of high critical density, n(H2) ≃ 104cm−3. Thus, we have made survey observations of the Galactic center region in the CS J=1-0 line with the Nobeyama 45-m telescope (Tsuboi, Handa, and Ukita 1997). The beamsize is 34″ and the achieved noise was Trms = 0.25 K/1.6 km s−1 in TMB. Then, we detected the molecular mass of M(H2)CS, thin = (3 − 8) × 107 M⊙ in the Galactic center molecular zone (CMZ), assuming of optically thin, Tex = 30 − 80 K (Güsten 1989), and X(CS) = 1 × 10−8 (Irvine et al. 1987).

As a key program of the 45-m telescope at Nobeyama Radio Observatory, we have made high-resolution CO images of the Galactic center region with the 2×2 focal plane array receiver. The data consist of 44,000 12CO and 13,000 13CO spectra taken with 16″ beams spaced by 34″. The 12CO image covers roughly −1.5° ≤ l ≤ +3.4° and −0.6° ≤ b ≤ +0.6° (Oka et al. 1997b)

We study the interaction of a dense giant molecular cloud with the HII region Sagittarius C, and a prominent nonthermal filament (NTF). For this purpose, we mapped the CS(2→1) and (3→2) transitions simultaneously with the IRAM 30m radio telescope, using the on-the-fly observing mode, and covering a 20pc×37pc (8′ × 15′) region. The high spatial resolution, 0.7pc (16″) at 147 GHz, allows for the first time to analyze in detail the morphology and kinematics of the molecular material and its relation to the ionized gas.

We have investigated the physical properties of molecular clouds which are presumably interacting with the G359.54+0.18 Nonthermal Filaments and an associated H ii region east of the filaments (Staguhn et al., 1996). The sub-mm spectra of 12CO(3-2) were observed with the KOSMA 3 m telescope, while the 490 GHz [C i] 3P1 →3P0 observations were made with the AST/RO 1.7 m sub-mm telescope. Fig. 1 shows channel maps of the integrated CO and [C i] line intensities in the velocity range of the recombination line observed towards the nearby H ii region. This H ii region is traced by the VLA 5 GHz continuum observations which are shown as contours in the central parts of the maps. The G359.54+0.18 Nonthermal Filaments, situated further to the west, appear to be morphologically associated with the H ii region. The [C i] emission of the molecular cloud east of the filaments which is kinematically linked to the H ii region is anti-correlated with the molecular line emission over a large angular extent. It is unlikely that the large morphological differences between [C i] and CO in this region can be explained exclusively by a high abundance of neutral carbon in the surface regions of dense molecular clumps, as is usually the case in PDR regions near the Sun.

Sgr B2 is one of the most active star-forming complexes in our Galaxy located ~100 pc from the Galactic center. Whiteoak et al. (1987) found that groups of the OH and H2CO masers and the compact HII regions are aligned in a north-south line, and suggested that star formation there is being triggered by a single large-scale event such as an interaction between molecular clouds. In order to investigate the total molecular cloud distribution and the triggering mechanism of the active massive-star formation in the Sgr B2 region, we mapped it in the 13CO and C18O (J = 1–0) lines with the Nobeyama 45 m telescope in 1988 March and May. In the 13CO line, an area was mapped of 345″ in right ascension and 495″ in declination covering the whole Sgr B2 molecular cloud at a grid spacing of 15″. In the C18O line, more restricted area was observed at 7.5″ or 15″ spacing. The HPBW of the 45 m telescope was 16″ at 110 GHz. Full description of the observations will be given elsewhere (Whiteoak et al. 1997).

We are conducting a survey of the CO J=2-1 line emission in the southern Milky Way (the Tokyo-Onsala-ESO-Calán Galactic CO survey), using the 60-cm radio telescope (VST2) in La Silla, Chile. It is combined with the northern survey made with the identical telescope (VST1) at Nobeyama (e.g., Sakamoto et al. 1995), and is directly comparable with the Columbia survey of the CO J=1-0 emission (e.g., Dame et al. 1987).

Sgr B2, located at a distance of ∼100 pc from the Galactic center, is one of the most active, recent massive-star formation regions in the Galaxy. Based on the 13CO (J = 1–0) line data taken with the Nobeyama 45 m telescope, we presented a cloud collision scenario as the triggering mechanism of the burst of massive-star formation there (Hasegawa et al. 1994). In order to obtain further evidence supporting our model, we observed the Sgr B2 molecular cloud in various molecular lines with the 45 m telescope in 1992 February. Twelve points each with 20″ spacings were observed along several strips 3.67′ long at constant galactic longitudes through the major HII region complexes. Here we report the results of the two lines in the 110 GHz band, C18O (J = 1–0) and HNCO (50,5–40,4). Full description of the observations will be given elsewhere (Sato et al. 1997).

G1.6-0.025 is a dense molecular cloud, located near the Galactic Centre at l=1.6° and b=−0.025°. Lacking in star-forming or infra-red regions, the cloud was first detected as a prominent 5-GHz H2CO absorption feature (Whiteoak & Gardner 1979). NH3 observations by Gardner et al (1985) revealed a clumpy cloud with a diameter of about 30 parsec, average LSR velocity of 50 km s−1, and a kinetic temperature exceeding 50 K. In addition, a high-velocity component at 160 km s−1 has been detected towards one of the clumps (Gardner & Boes 1987). CH3OH in the cloud gives rise to a 12-GHz 20−3_1 E transition in absorption, representing the best example of rare population ‘anti-inversion’ for this transition (Whiteoak & Peng 1989; Peng & Whiteoak 1993). In contrast, the 36-GHz 4−1−30 E transition shows extended emission with superimposed knots containing maser emission (Haschick & Baan, 1993). Sobolev (1996) has suggested that a collision! has occurred between the main cloud and another cloudlet with relative velocity of 100 km s−1, resulting in high kinetic temperatures and shock waves that create the CH3OH masers.

Data : We used the Galactic center region survey data in CS J=1-0 with the Nobeyama 45-m telescope (Tsuboi, Handa, and Ukita 1997).

Cloud Definition : We identified molecular clumps in the positive longitude region of about ∼1deg2 (+0°10′ < l< + 1°42′ and −25′ < b< +25′) within all survey region.