Recent CO studies of spiral galaxy NGC 4258 have revealed a close relationship between the molecular gas and the anomalous arms, recently interpreted as jets (Cecil et al. 1992, Martin et al. 1990). An IRAM single dish study by Krause et al. (1991) showed the CO to be concentrated around the Hα arms. Interferometrie imaging of the inner 1’ by Martin et al. (1990) showed the molecular gas confining the arms; they suggested that the jet had initially plowed a tunnel through the disk gas, producing a free path for subsequent ejections. This data also shows strong evidence for a jet-cloud collision along the N W arm (Piante et al. 1991).

To learn more about the jets, we are motivated to exploit the jet-gas relationship with multi-field imaging of the CO along the anomalous arms using the Nobeyama Millimeter Array. We present preliminary results from our first 60” field, centered on the SE Hα arm, 43.5” from the nucleus. Observations in the two most compact configurations (C and D) produced a 4” x 6” beam.

Most of observational researches on molecular gas in galaxies have focused on the two-dimensional distributions in galactic disks so far. In order to investigate vertical structure of the galactic disk and the disk-halo interaction we need high-resolution observations of edge-on galaxies.

So we observed the nearest edge-on galaxy, NGC 891, using the Nobeyama Millimeter Array (NMA). Its distance is estimated to be 8.9 Mpc using the Tully-Fisher relation and H-band photometric data. The synthesized beamsize was 4.5” x 4.4” and the field of view due to attenuation of the element antenna (Handa et al. 1992). The field center is 90”-offset from the center of the galaxy along the major axis toward the northern side, where the CO intensity has a local maximum (Sofue et al. 1987). After the standard data reduction procedure in AIPS, including CLEAN, we obtained 10 channel-maps with a 19.5 km s−1 velocity width from 289.8 km s−1 to 465.2 km s−1 with respect to the local standard of rest.

In the integrated intensity map a narrow CO emission ridge is seen (Figure 1). It is an edge-on view of molecular gas disk of the galaxy. The confinement of the CO emission in the thin disk suggests that most of the molecular gas is belonging to the population-I objects like in our Galaxy. The apparent thickness of the ridge is about 7”, which means that the deconvolved width is about 6” or 270 pc (FWHM). The position-velocity diagram averaged along the major axis over the field of view shows no systematic velocity gradient along the minor axis (Figure 2). It means that the deconvolved thickness of the CO disk is intrinsic. This width is broader than that of our Galaxy by factor 2. The geometrically thick CO disk of NGC 891 may be due to active star formation in the disk.

The late-type edge-on spiral galaxy NGC 4631 is known for its high star formation rate and extended radio halo with a uniform magnetic field component ordered predominantly perpendicular to the plane of the galaxy in the inner 6 kpc (assuming a distance of 7.5 Mpc, 1′ = 2.2 kpc) (Hummel et al. 1988; Golla, Ph.D., in preparation). The strongest radio continuum source of NGC 4631 is located at the eastern edge of the central region near a giant HII region complex CM67 (Crillon and Monnet 1969). The magnetic field orientation going out from the central region and especially from the region CM67 as well as the prominent north eastern low frequency radio spur (cf. Hummel et al. 1991) indicate a close connection between the synchrotron emission of the radio halo of NGC 4631 and star forming regions/CM67 in the disk (Golla and Hummel, in preparation). Probably cosmic rays from star forming regions in the disk propagate along the magnetic field Unes into the halo.

The conversion factor from the CO line intensity to column density of molecular hydrogen, X = NH2/ICO is one of the most important parameters in mm-wave study of galaxies and their molecular gas (e.g., Maloney 1990). Although the same value as that obtained for our Galactic clouds (e.g. Sanders et al. 1984; Bloemen et al. 1985) has been widely applied to galaxies, it is far from trivial that the conversion factor is universal among various types of galaxies. There have been few attempts to derive the value for galaxies, and the value is still controversial if it is applicable to other galaxies or not: Approximately the same value as that for the Galaxy has been derived for M33 (Wilson and Scoville 1990, 1992), while an order of magnitude larger value is obtained for the LMC and SMC (Cohen et al. 1988; Rubin et al. 1991).

In order to obtain the conversion factor in nearby galaxies, in which individual molecular clouds can be resolved, we are conducting CO-line mapping of M31. In this paper we report a preliminary results from mapping of a north-eastern spiral arm of M31 in the 12CO(J =1 − 0) line emission using the NMA.

The Tully-Fisher relation makes use of the correlation between the HI linewidth and the luminosity of a galaxy and is one of the most powerful tools to estimate distances of galaxies. Because of the smaller beam the CO line might be an alternative to HI for distant galaxies which so far can not be examined even by the largest telescopes (Dickey and Kazes 1992).

In order to consider the question whether the CO lineprofile could be used as an alternative or a supplement for HI in the Tullly-Fisher relation, we compared the total CO (J=2-1) line profiles of ten galaxies with the corresponding HI profiles. Four almost perfect edge-on galaxies (NGC 891, NGC 4565, NGC 4631 and NGC 3079) and the Seyfert galaxy NGC 1808 have been observed in CO using the Nobeyama 45-m telescope. The HI profiles and the data of the other galaxies has been taken from the literature.

Near infrared imaging can be a powerful tool in tracing the densest molecular structures in galaxies. The observable molecular emission originates in large molecular cloud complexes which are also subject to significant extinctions caused by the associated dust. It can be difficult to distinguish between regions of moderate and large molecular density with optical observations as both will appear optically thick. Since extinction in the near infrared is only about a tenth of the corresponding visual extinction, multi-band near infrared imaging will trace the regions of the highest optical depths much more effectively. With the advent of large format infrared imaging arrays it is now possible to use infrared extinction maps as a probe of the large scale distribution of molecular emission in extragalactic sources.

An interaction of two masers through plasma longitudinal waves in the Stimulate Raman Scattering has been investigated and applied for the extreme high-velocity (900 km s-1) water masers discovered in NGC 4258. For the stimulated Raman scattering, the frequency down-shifted components are easily created but not the up-shifted components. We use the interacting masers for the explanation for the presence of the up-shifted components. The interaction occurs when the wave vector of the longitudinal plasma wave associated with one incident maser coincides with the wave vector of the other longitudinal wave associated with the other maser. This interaction produces two daughter waves, frequency up-shifted and down-shifted radiations with a shift of roughly a plasma frequency. This interaction occurs when two masers intersect with intersecting angle of about 176 degree in plasma of the electron density of about 5 106 cm-3. The brightness temperature of the original incident masers must be greater than about 1013 K (depending on the line width, and the maser beaming angle, etc.) and the scale length of plasma must be larger than about 1013 cm.

Since molecular gas clouds in nuclear regions play important roles on both the intense star formation and fueling active galactic nuclei, a large number of molecular-line observations have been made for starburst, Seyfert, and merging galaxies. Recently, millimeter-wave arrays have been used to study circumnuclear molecular gas in merging galaxies. Most of them, however, have been devoted to the observations of more luminous objects such as ultra-luminous merging galaxies (ULMGs) discovered by IRAS (Sanders et al. 1988). In order to obtain a comprehensive understanding, it is necessary to study less-luminous merging galaxies. With this motivation, we present results of CO mapping of NGC 3310 which is one of less luminous merger candidates (LFIR = 2.5 × 1010Lʘ).

The central region (5.1 kpc in diameter) of NGC 3310 was observed in CO(J = 1 − 0) using the Nobeyama Millimeter Array. The synthesized beam size was 6″.3 × 6″.1, which corresponds to 500 × 480 pc at the distance 16.3 Mpc. Our main results and conclusions are summarized as follows.

We made aperture synthesis CO(l-O) observations of the central region of Arp220 with the Nobeyama Millimeter Array. Central CO emission was resolved with a size of 975 kpc. It shows a ring-like structure (ɪ ~ 500 pc) with a large velocity gradient, 393 km · s−1 · kpc−1, from southwest to northeast direction. The ring-like emission is located around double radio compact sources. No emission peak was found in the center of the double sources within the velocity range 5100 km s−1to 5800 km s−1. These results suggest that an inclined massive gas ring has been or is being formed in the central 1 kpc of Arp220. Most of the molecular gas in Arp220 is concentrated on this nuclear ring. The radio compact sources are probably located at the inner egde of the ring.

We have observed CO(J=3-2) emission of the z=2.286 galaxy IRAS F10214+4724 using the Nobeyama Millimeter Array.

We have been awarded NASA funds to construct a Submillimeter (SMM) Array Photometer for use at the Caltech SMM Observatory (CSO) on Mauna Kea. The array will consist of 5×5 composite bolometers illuminated through light cones. On the CSO, each cone will cover 25 arcsecs on the sky, implying a total field-of-view for the array of just over 2×2 arcmins. Our aim is to achieve background-limited performance in the 730 and 870 μm atmospheric windows, thus obtaining a Noise Equivalent Flux Density (NEFD) of approximately 0.1 Jy/√Hz at these wavelengths. This sensitivity level will enable 5-sigma measurements of 10 mJy sources (such as radio-quiet quasars) in about one hour. We also will have the capability to operate at 1.1 mm, but the photometer will not be optimized at this wavelength. This system is expected to be operational on the CSO in January 1994.

The Smithsonian Astrophysical Observatory is currently designing and constructing the Submillimeter Array (SMA). This instrument will consist of six 6-m telescopes, which can be moved and reconfigured in four concentric ring-like arrangements with maximum baselines of 500 m. Pending negotiations, the SMA will be sited on Mauna Kea at the 4000 m plateau, adjacent to the existing CSO and JCMT submillimeter telescopes. The goal of the SMA is to provide imaging at sub-arcsecond resolution for the wavelength range of 1.3 mm to 0.35 mm. This instrument will therefore improve the angular resolution achieved with present submillimeter telescopes by more than an order of magnitude. As the cool (10-100 K) dust and gas in the Milky Way and other external systems will radiate principally in the submillimeter wavelengths, we expect the SMA to provide unprecedented resolution and to make fundamental contributions to many different problems including the studies of our solar system, star formation and circumstellar disks, galaxies and molecular cloud structures, quasars and active galactic nuclei, and perhaps even galaxy formation in the early universe.

It is shown that multi-elements surface of the Russian biggest reflector may be considered as a 1000-element array with limited freedom of motions of each element. This limitation may be compensated by selection of the proper “virtual sub-array” of elements at any given direction of observations. This approach is especially effective for mm-waves where field of view of 600-meter reflector in usual mode is less than 1 arcsec. The present stage of realization of that project is shortly discussed, including requirements for multi-feed system near the focal plane of the radio telescope, wavelength limitations and error budget, and near field zone 3-dimensional synthesis mode of observation.

The Millimeter Array, under development in the United States, is a fast and flexible telescope capable of imaging the thermal sky at a resolution equal to that specified in the design goals of the Hubble Space Telescope. The MMA is a project of the U.S. National Science Foundation, and it has been highlighted as one of the four major U.S. initiatives in astronomy for the decade of the 1990s. Construction will begin toward the end of the decade at a site soon to be chosen.

In Japan, there is a plan for Large Millimeter Array proposed by Nobeyama Radio Observatory. The proposed array may consist of 50 10-m antennas distributed in a 2 − 3 km area at very high altitude. In this paper, scientific directions, planned system, and site survey for the LMA are reported.

The southern night sky is a sight of overwhelming beauty. It is hard to forget one’s first view of the night sky from La Silla with the Galactic centre overhead and the brilliant constellations of Sagittarius and Scorpius with their bright stars and copious amounts of dust. In fact for a millimetre astronomer, it is the dust that is so striking and one feels for the first time that one is seeing tangible visual evidence of the intriguing molecular clouds that dominate our discipline.

Ironically it is the observation of these southern molecular clouds that have shaped much of millimetre radio astronomy, yet we persist in observing them from the northern hemisphere through many air masses of atmospheric attenuation.

Having built the Swedish ESO Submillimtre Telscope, SEST in the south, on La Silla, in Chile, Swedish and other European astronomers would like to follow up this initiative with a southern hemisphere millimetre array, taking advantage of the excellent dry mountain sites. There is much to be done with such an instrument.

Radiation from the gaseous disk of a galaxy like the Milky Way principally occurs via fine structure transitions of carbon, oxygen, and nitrogen, all of which occur at submillimeter wavelengths at which the earth’s atmosphere is opaque. Indeed, more than ten percent of all the energy radiated by the stars and gas in the Milky Way comes out in the 1900 GHz line of once ionized carbon! This line can only be observed from space, and it can only be observed with arcsecond angular resolution with a space-based interferometer. The international space station Freedom provides a stable platform, with the right dimension, for the necessary submillimeter interferometer.

This paper draws attention to the potential for use of telescopes now under construction or planned for the near future as part of the Mt. Graham International Observatory, located in the Pinaleño Mts. east of Tucson, Arizona, for interferometer observations at mm-and submm-wavelengths. The Submillimeter Telescope (SMT) should be completed by early 1993. A collaboration between the Max-Planck-Institut für Radioastronomie and Steward Observatory, the SMT is a high-precision 10-m diameter telescope which will be useful for short-wavelength VLBI observations. A large optical telescope, consisting of two 8.4-m diameter mirrors on a common mount, is in the early design stages. When completed, it will provide for short-baseline (approx. 20-m) interferometry between the two optical mirrors, as well as interferometry with the SMT over baselines of a few hundred meters.

SOFIA will be a 2.5 meter telescope installed in a Boeing 747 aircraft. It will replace NASA’s smaller Kuiper Airborne Observatory (KAO), which for the past 18 years has provided the only routine access to most of the vital infrared spectrum (1 - 1000 µm). The aircraft platform opens a valuable window to the universe by enabling measurements of infrared radiation from celestial sources which the Earth’s atmosphere absorbs at lower altitudes. SOFIA will have 10 times the sensitivity and 3 times the angular resolution of the KAO throughout most of the infrared spectrum.

SOFIA will be operated during its 20 year lifetime as an international facility for astronomy. It would fly 160 astronomy missions per year for about 50 science teams, selected by annual peer review. Nearly a third of these teams will furnish the observatory with specialized instrumentation, including array cameras, polarimeters, and several types of spectrometers. The frequent flight opportunities with state-of-the-art instruments guarantee extensive community participation and hands-on training of young scientists.

A high time- and spatial-resolution radio interferometer for solar observations has been constructed at Nobeyama (Figure I.; Nakajima et al. 1994). The Nobeyama Radioheliograph consists of 84 antennas, 0.8m in diameter, arranged on a T-shape lines of 500m in the EW and 220m in the NS directions. The time resolution is 50 ms and the spatial resolution is 10”. The field of view is 40’ at the observing frequency 17GHz, which enables us to watch the whole sun. The radioheliograph has observed hundreds of flares during the few months since the beginning of regular observations in July ‘92, and such powerful performance has never before been demonstrated in the history of solar radio observations.