坪井 昌人

The data from the Nobeyama Radio Observatory 45 m telescope Galactic Center CO survey have been analyzed to generate a compilation of molecular clouds with intense CO emission in this region. Clouds are identified in an automated manner through the main part of the survey data for all CO emission peaks exceeding 10 K (TR*). The measured parameters of identified clouds are analyzed and cross-correlated to compare with those of clouds in the Galactic disk. For the clouds in the Galactic center (GC), we find the scaling laws of the type σV ∝ S0.40 and MVT ∝ (LCO)0.88, which are similar to those of clouds in the Galactic disk. All the GC clouds identified have larger velocity widths and virial theorem masses each above the σV-S and LCO-MVT lines of the disk clouds. We diagnosed gravitational stabilities of identified clouds assuming that the disk clouds are nearly at the onset of gravitational instability. All the clouds and cloud complexes in the GC are gravitationally stable, indicating they are in equilibrium with high pressure in the GC environment. Gravitationally less stable clouds follow the main ridge of intense CO emission, part of which define two rigidly rotating molecular arms. The velocity dispersion of a cloud correlates inversely with the degree of gravitational instability. It is concluded that mechanisms such as orbit crowding at the inner Lindblad resonance may promote gravitational instability and subsequent star formation. © 2001. The American Astronomical Society. All rights reserved. Printed in U.S.A.

We present statistical properties of molecular clouds based on the Galactic center region survey in CS J = 1-0 with the 45 m radio telescope of the Nobeyama Radio Observatory. We identified 159 molecular cloud clumps from the survey data. We found that the velocity widths of the Galactic center molecular clumps are about 5 times larger than those of the Galactic disk molecular clouds with the same radius. We estimated the virial theorem masses and the LTE masses of the identified clumps. The virial-theorem masses are 1 order of magnitude larger than the LTE masses. We obtain the mass and size spectra for the Galactic center molecular clumps. The mass spectrum is dN/dM ∝ M-1.6±0.1(M ≳ 1.0 × × 104 M⊙). The spectral index was approximately equal to the values obtained in the Galactic disk regions, although the statistical relations, such as the line width-size relation, for the Galactic center clouds are much different from those for the disk clouds. The size spectrum is dN/dR ∝ R -4.0±0.4 (R ≳ 3.3 pc). The spectral index is consistent with those for the disk clouds.

We have an on-going observation project of the Sunyaev-Zel'dovich (S-Z) effect using a 40-50 GHz focal-plane array SIS receiver installed in the Nobeyama 45-m telescope in order to measure Hubble constant. The receiver have 6 beams located at 2×3 grids of 90 inches interval and have a typical receiver noise temperature of 40 K. We are improving the array receiver to increase the observing efficiency by reducing of the receiver noise temperature and increasing of the IF bandwidth. The direct connection of IF amplifier and SIS mixer should realize these performances. However, this may introduce impedance mismatch and heat flow from the IF amplifier to the SIS mixer. We tested a SIS mixer with an one-stage HEMT IF amplifier. There was no severe temperature increase in the SIS mixer. The impedance mismatch may make some undulations in the IF output character. The SIS receiver were operated with equivalent performance to the original SIS mixer in LO frequency range of 42.5 to 48.5 GHz and in IF frequency range of 1.1 to 2.5 GHz.

We present the results of high-resolution imaging of the gamma-ray loud quasar PKS 1741-038 with the HALCA satellite and ground radio telescopes. Observations were made at two epochs at an interval of nine months with the first-epoch observation at 1.6 and 5 GHz and with the second-epoch observation at 5 GHz. The source shows a very compact structure, but is clearly resolved in the space-ground baseline visibility data. The core component of the source has a brightness temperature, Tb, greater than 1012 K in the source's rest frame at each frequency. We applied three individual jet models in order to derive the Doppler factor, δ. The core component has δ ∼ 14, considering the Tb limit due to the inverse Compton catastrophe, while a 2.5-times larger δ is obtained assuming that the particles and magnetic field are in equipartition. Two-epoch images at 5 GHz show almost no change of the structure. Assuming that the component motion in this interval is less than our resolution, we derived the upper limit of the viewing angle as being 4.°8. The smaller viewing angle and higher Doppler factor favor the inverse Compton gamma-ray emission model; we conclude that the gamma-ray emission from this source is highly Doppler-boosted.

We report the detection of a peculiar molecular cloud, CO 0.02-0.02, lying about 5′ Galactic east from the center of the Galaxy. 12CO images taken with Nobeyama Radio Observatory (NRO) 45 m telescope showed that it is relatively compact (∼3 × 4 pc2) as well as having a very large velocity width (ΔV ≥ 100 km s-1). The cloud has a virial mass about 1 order of magnitude larger than the LTE mass, 9 × 104 M⊙, indicating the cloud is apparently gravitationally unbound. New observations with the James Clerk Maxwell Telescope 15 m and the NRO 45 m telescopes show that CO 0.02-0.02 is very bright in the CO (J = 3-2) and in the HCN and HCO+ (J = 1-0) lines. It appears that the environment may have an unusually high density and temperature, which may be related to the very broad CO line width. We propose that CO 0.02 -0.02 may have been accelerated, heated, and compressed in a series of supernovae shocks that have occurred within the last (3-5) × 104 yr.

We have performed 3 sets of one-month intensity monitor observations toward Sgr A*, at v = 100 and 140 GHz from 1998 to 1998 using the Nobeyama Millimeter Array. We got following results; 1) We detected a flare of Sgr A* in March 1998. The flux density at v = 100 GHz was flared over (Delta S/S =) 100% in a week and decreased to the mean flux density within two weeks. @The flux density in the flare at v = 140 GHz was also increased over (Delta S/S =) 100%. 2) The flux densities in the hare are consistent with the power-law spectrum of alpha = 0.6(S proportional to v(alpha)). On the other hand, the mean flux densities in quiescent phase in 1996-1998 are consistent with the power-law spectrum of alpha = 0.3.

The data from the Nobeyama Radio Observatory 45 m telescope Galactic Center CO survey have been analyzed to generate a compilation of molecular clouds with intense CO emission in this region. Clouds are identified in an automated manner throughout the main part of the survey data for all CO emission peaks exceeding 10 K (T* R ). Correlations between the size, velocity dispersion, virial mass, and the CO luminosity, for the molecular clouds in the Galactic center were shown. We diagnosed gravitational stabilities of identified clouds assuming that the disk clouds are nearly at the onset of gravitational instability. Most of the clouds and cloud complexes in the Galactic center are gravitationally stable, while some clouds with intense CO emission are gravitationally unstable. @1999 COSPAR. Published by Elsevier Science Ltd.

We have performed 3 sets of one-month intensity monitoring observations toward the Galactic center compact nonthermal radio source, Sagittarius A*, at λ=3 and 2 mm (100 and 140 GHz) from 1996 to 1998 using the Nobeyama Millimeter Array. In March of 1998, we detected a flare in Sgr A* . The flux density at 100 GHz was flared up by more than 100% (ΔS/S) in a week, then decreased to a mean flux level in two weeks. The flux density at 140 GHz during the flare also increased by more than 100% (ΔS/S). © 1999 COSPAR. Published by Elsevier Science Ltd.

We have observed a 160′ × 40′ (l × b) region around the Galactic center in the CS J = 1-0 line with a high spatial resolution and high sensitivity using the 45 m telescope at Nobeyama Radio Observatory. The observed area includes the Sgr A radio arc complex, Sgr B, Sgr C, and Sgr D. About 24,000 spectra of CS J = 1-0 emission, which is a good tracer of high-density (n ≅ 104 cm-3) molecular clouds, were obtained. The observed data are presented in l-b, l-v, and b-v maps. The total CS line flux in this area is ∫ S dv = 1.1 × 106 Jy km s-1. Typical optical thickness of C32S J = 1-0 emission is equal to or lower than τ = 2-3. The total molecular mass in the Galactic center region is estimated to be M(H2) = (3-8) × 107 M⊙ from the assumption of LTE. One-third of the molecular clouds in the Galactic center region are involved in several continuous curved ridges extended along the Galactic longitude. The most prominent ridge has a "bow"-like structure with a length of 300 pc.

We report statistical properties of molecular clouds in the Galactic center region. We identified 65 molecular clumps in the region. We determined the velocity width-radius relation and the virial mass-LTE mass relation for the identified Galactic center clumps. We also determined the mass and size spectra for the Galactic center clumps. We consider whether the Galactic center molecular clumps is bound by the external pressure and/or the magnetic field. © 1999 COSPAR. Published by Elsevier Science Ltd.

We have searched for the CO (J = 1-0) line emission toward the gravitational lensed "Cloverleaf" quasar, H1413+117, at z = 2.56 using the 45-m telescope of Nobeyama Radio Observatory. The r.m.s. noise of the resultant spectrum was 1 σrms = 0.6 mK in TMB or 1.6 mJy for a velocity resolution of 50 km s-1. We obtained the 5 σrms upper limit of the velocity-integrated CO (J = 1-0) line flux, ∫ S1-0dv < 1.4 Jy km s-1. The lower limit of the intrinsic ratio of the brightness temperature is TB[CO (J = 3-2)]/TB[CO (J = 1-0)] > 0.79 at z = 2.56. This value corresponds to TB[CO (J = 3-2)]/TB[CO (J = 1-0)] > 0.72-0.75 at z = 0 from a LVG calculation. This temperature ratio is consistent with those in the central regions of nearby IR luminous galaxies.

We have designed and constructed a tunable polarimeter to cover frequencies from 35 GHz to 250 GHz (8.6 mm and 1.2 mm in wavelength) for the 45-m telescope at Nobeyama Radio Observatory. Both circular and linear polarizations can be measured by the polarimeter. The insertion loss was measured to be 0.14 ± 0.05 dB in the 100-GHz band. The overall instrumental polarization of the system in the 100 GHz band is as low as ≤ 3%. The performance of the polarimeter in astronomical observations was tested by simultaneously measuring the linear polarization of the J = 2-1 transition of SiO in the v = 0 and 1 states at 86 GHz toward VY Canis Majoris. The observation revealed that the J = 2-1 emission in the v = 0 state of the object is highly linear polarized, which suggests that the emission originates through maser action in the circumstellar region. The details of the design, construction, and tests are presented.

We present high-resolution CO images of the Galactic center region taken with the 2 × 2 focal-plane array receiver mounted on the 45 m telescope of Nobeyama Radio Observatory. We have collected about 44,000 12C16O (J = 1-0) spectra and over 13,000 13C16O (J = 1-0) spectra with a 34″ (1.4 pc) grid spacing. The 12CO mapping area is roughly - 1°.5 ≤ l ≤ + 3°.4 and -0°.6 ≤ b ≤ +0°.6, which covers almost the full extent of the molecular gas concentration in the Galactic center. These CO images demonstrate extremely complex distribution and kinematics of molecular gas in the Galactic center. While its large-scale behavior can be attributed to the well-known coherent features, bright CO emission arises from a number of compact (d ≤ 10 pc) clouds with large velocity widths (ΔV ≥ 30 km s-1). The small-scale structure of molecular gas is characterized by filaments, arcs, and shells. The boisterous molecular gas kinematics there may be a result of violent release of kinetic energy by a number of supernova explosions and/or Wolf-Rayet stellar winds.

We present preliminary results from the observations of the Galactic Center compact source, Sgr A* at 3 and 2 millimeter wavelengths using the Nobeyama Millimeter Array to monitor flux density variations on timescales shorter than a month. Such high spatial resolution observations at millimeter wavelengths are important to shed more light on the origin of the variability and the nature of this compact source. Our observations indicate the flux density varies at least by similar to 30% in one to two weeks at 3 mm.

We developed a 40-50 GHz array receiver which has six feed horns (2×3 array) and six superconducting-insulating-superconducting (SIS) mixers. We used tunerless SIS mixers to make the tuning system simple and to achieve the high stability. The receiver system is designed as a sophisticated tool for continuum observation of the Sunyaev-Zel'dovich effect toward clusters of galaxies. The receiver noise temperature is 20-30 K. The instantaneous band width is 700 MHz. This system is installed on the focal plane platform of the Nobeyama45-m telescope. We did a test observation to evaluate the performance of the receiver system. The estimated DSB system noise temperature were 110-170 K at 43 GHz. The aperture efficiency and the main-lobe efficiency of this system were 0.4-0.6 and 0.5-0.9, respectively.

We constructed a new reflective-type polarimeter system at 35-250 GHz for the 45 m telescope at Nobeyama Radio Observatory (NRO). Using the system, we can measure both linear polarization and circular polarization for our needs. The new system has two key points. First is that we can tune the center frequency of the polarimeter in the available frequency range, second is that insertion loss is low (0.15±0.03 dB at 86 GHz). These characteristics extended achievable scientific aims. In this paper, we present the design and the performance of the system. Using the system, we measured linear polarizations of some astronomical objects at 86 GHz, with SiO v = 0,1 and 2 at J = 2-1 and 29SiO v = 0 J = 2-1 simultaneously. As a result, the observation revealed SiO v = 0 J = 2-1 of VY Canis Majoris is highly linearly polarized, the degree of linear polarization is up to 64%, in spite of SiO J = 2-1 v = 1 is not highly linearly polarized. The highly linearly polarized feature is a strong evidence that 28SiO J = 2-1 transition at the ground vibrational state originate through maser action. This is the first detection of the cosmic maser emission of SiO v = 0 J = 2-1 transition.

We performed a millimeter-wave observation of the Sunyaev-Zel'dovich effect toward a moderately distant cD cluster of galaxies, Abell 2218, at 36 GHz using the Nobeyama 45-m telescope. The antenna temperature decrement of the cosmic microwave background radiation (CMB) was measured to be ΔT*A; = -0.52 ± 0.15 mK at the central peak position of X-ray emission in the cluster. Assuming that the hot gas in the cluster has isothermality, spherical symmetry, and the β-model density distribution, the Sunyaev-Zel'dovich effect is inferred to be ΔT0RJ = -0.68 ± 0.19 mK at the Rayleigh-Jeans limit. A combination of this Sunyaev-Zel'dovich effect and X-ray surface brightness suggests that the Bubble constant is H0(q0 = 0.5) = 54+51-21 km s-1 Mpc-1.

We have made high resolution mapping observations of (CO)-C-12 (J=1-0) and (CO)-C-13 (J=1-0) from the central few hundred parsecs of the Galaxy using the NRO 45m telescope (HPBW=16''). The high resolution CO maps reveal many molecular are and/or shell structures which could have resulted from interactions with supernovae. We also found a large (radius similar to 50 PC) ring structure surrounding the region of diffuse X-ray emission, expanding at V-EXP similar or equal to 200 km s(-1). This and other evidence suggest that a galactic superwind following a burst of star formation in the recent past is sweeping up the ambient gas. The Galactic center may have experienced a burst of star formation similar to 5 x 10(7) years ago, and it may be in post-starburst phase now.

We found, from the data of our CS (J = 1-0/2-1) survey with the Nobeyama 45 m telescope, that a molecular cloud associated with the "vertical filaments" of the Galactic center arc has a shell-like structure and is expanding with a velocity of 20 km s-1. The limb of the shell has high density, n(H2) = 6 × 104 cm-3. The shell may have originated from 10-100 supernovae within the last 105 yr. At the point of contact with the filaments, the limb of the shell is deformed and the filaments are bent in the opposite direction. These compensative deformations suggest that the shell is dynamically interacting with the filaments. The interaction may activate relativistic electrons in the Galactic center arc. © 1997. The American Astronomical Society. All rights reserved.

We observed the distribution of the Stokes Ir parameter and the Linear polarization in the Galactic Center Are-Polarized Plumes Complex region at 42.5 GHz with a newly developed 40-GHz band polarimeter equipped on the Nobeyama 45-m telescope. The Galactic Center Are at 42.5 GHz is highly polarized up to p = 50%. The magnetic fields with a 120 '' resolution in the Galactic Center Are are well ordered and are generally along the Vertical Filaments. The spectral indices between 10 and 42.5 GHz gradually become steeper going from the Galactic Center Are to both Polarized Plumes, although the complex has a flat spectrum between 2.7 and 10 GHz. The relativistic electrons may be accelerated in the Galactic Center Are and gradually drift along the poloidal magnetic field toward the Polarized Plumes with synchrotron-loss. The linear rotation of the polarization angle as the wavelength square and the depolarization properties between 10 and 42.5 GHz suggest a large internal Faraday rotation, RM = - 3000 rad m(-2), in the Galactic Center Arc.

The Nobeyama 45-m telescope has been upgraded for higher frequency and higher sensitivity observations. The surface accuracy of the antenna was improved from 0.2 mm rms to 65 µm rms using a radio holography method at the prime focus. Pointing accuracy was also improved by replacing a large Gregorian subreflector cabin with a smaller cassegrain subreflector in 1985 to reduce wind loading effects, and by installation of a new master collimator with multi-pole resolvers which were calibrated to an accuracy of 0.4 arcsec rms in 1988. Four SIS receivers using Nb/AlOx/Nb array junctions are now available on the telescope for 40, 80, 100, and 150-GHz bands. These receivers achieved quite low noise and wide-band tunability. The 2 × 2 multi-beam receiver for 115 GHz is very powerful for mapping observations. These improvements of telescope performance and these receivers have significantly increased the astronomical observation capability of the telescope in the wide frequency range of 40 to 150 GHz. © 1994 IEEE.

We have detected a strong CO (J = 1-0) emission line toward the high-redshift compact group of galaxies IRAS F10214+4724 using the Nobeyama 45-m telescope. The integrated line flux is 2.4+/-0.3 Jy km s-1. The total molecular mass producing the CO (J = 1-0) emission was estimated to be (1.8-6.4) x 10(11) h-2M.. The brightness temperature ratio of CO (J = 3-2) to CO (J = 1-0) suggests that a huge mass of molecular material in IRAS F1014+4724 exists as low-density molecular gas of n(H2) congruent-to 10(2) cm-3, or that the CO (J = 1-0) emission is distributed by more than 16'' (64h-1 kpc).

We have observed the 22.3-GHz continuum emission of the Sgr C complex using the Nobeyama Millimeter Array. We found that the Sgr C complex has a U-shaped ridge comprising several clumpy features as well as shell-like features. The spectral index of these features suggests optically thin thermal emission embedded in the nonthermal component. A bar-like structure, noticed in a previous 1.7-GHz continuum observation, is already very weak at 22.3 GHz. The steep spectrum of this bar-like structure is consistent with a nonthermal origin. The Sgr C complex is located at the end of the elongated molecular cloud in the Galactic center region. The close relations of morphology and velocity between the Sgr C complex and the molecular cloud suggest that the Sgr C complex is an H II region physically interacting with the molecular cloud in the Galactic center region.

We have searched the CO J = 1-0 absorption line of a damped Ly-alpha absorber at z = 2.04 toward the QSO PKS 0458-02 using the 45-m telescope of Nobeyama Radio Observatory. We obtained the upper limits of the optical thickness as 0.024 and 0.014 at velocity resolutions of 2 and 5 km s-1, respectively. The upper limit of the column density of CO molecules (N(CO)) is 2.1 x 10(15) cm-2 for an optical thickness (tau) of 0.024 and an excitation temperature (T(ex)) of 20 K.

Characteristics of a millimeter-wave mixer with Nb/ AI-A10x/Nb SIS junction were calculated along the 3-port mixer treatment. Signal and intermediate frequency dependences are obtained. The results show that the mixer has conversion gain between signal frequencies of 30 and 250 GHz. Intermediate frequency up to 10 GHz can be used in the USB mode. © 1987 IEEE.

A 40 GHz band SIS mixer receiver has been built using Nb/Al-AlOx/Nb array junctions and a 4.3 K closed cycle helium refrigerator. The minimum conversion loss of the mixer is 2±1 dB and the single sideband receiver noise temperature (TRX (SSB)) is as low as 110±10 K at 36 GHz. TRX (SSB) is almost constant in the IF bandwidth of 600 MHz. The mixer saturation level is as high as 15 nW, which is comparable to the injected LO power. © 1987 Plenum Publishing Corporation.