Researcher Database

Kazuo Sorai
Faculty of Science Physics Quantum Physics
Associate Professor

Researcher Profile and Settings

Affiliation

  • Faculty of Science Physics Quantum Physics

Job Title

  • Associate Professor

Degree

  • Doctor(Science)(The University of Tokyo)

J-Global ID

Research Interests

  • 電波天文学   星間物理学   銀河物理学   Radio Astronomy   Interstellar Physics   Galactic Astronomy   

Research Areas

  • Natural sciences / Astronomy

Academic & Professional Experience

  • 2017/04 - Today University of Tsukuba Faculty of Pure and Applied Sciences Associate Professor (cross appointment)
  • 2012/04 - Today Hokkaido University Faculty of Science Associate Professor
  • 2007/04 - 2012/03 Hokkaido University Faculty of Science Assistant Professor
  • 2006/04 - 2007/03 Hokkaido University Faculty School of Science Research Associate
  • 2002/05 - 2006/03 Hokkaido University Graduate School of Science Research Associate
  • 2002 - Research Associate, Graduate School of
  • Science, Hokkaido University

Association Memberships

  • International Astronomical Union   日本天文学会   the Astronomical Society of Japan   

Research Activities

Published Papers

  • The Dust-Selected Molecular Clouds in the Northeast Region of the Small Magellanic Cloud
    Takekoshi, T, Minamidani, T, Komugi, S, Kohno, K, Tosaki, T, Sorai, K, Muller, E, Mizuno, N, Kawamura, A, Onishi, T, Fukui, Y, Bot, C, Rubio, M, Ezawa, H, Oshima, T, Austermann, J. E, Matsuo, H, Aretxaga, I, Hughes, D. H, Kawabe, R, WILSON, G. W, Yun, M. S
    The Astrophysical Journal 2018/09 [Refereed][Not invited]
  • VERA monitoring of the radio jet 3C 84 during 2007--2013: in the period of non-linear motion
    Hiura, K, Nagai, H, Kino, M, Niinuma, K, Sorai, K, Chida, H, Akiyama, K, D’Ammando, F, Giovannini, G, Giroletti, M, Hada, K, Honma, M, Koyama, S, Orienti, M, Orosz, G, Sawada-Satoh, S
    Publications of the Astronomical Society of Japan 2018/07 [Refereed][Not invited]
  • A Face-on Accretion System in High-mass Star Formation: Possible Dusty Infall Streams within 100 AU
    Motogi, K, Hirota, T, Sorai, K, Yonekura, Y, Sugiyama, K, Honma, M, Niinuma, K, Hachisuka, K, Fujisawa, K, Walsh, A. J
    The Astrophysical Journal, 849 (1) 23:1 - 23:13 2017/11 [Refereed][Not invited]
  • Diverse nuclear star-forming activities in the heart of NGC 253 resolved with ten-pc scale ALMA images
    Ando, R, Nakanishi, K, Kohno, K, Izumi, T, Martin, S, Harada, N, Takano, S, Kuno, N, Nakai, N, Sugai, H, Sorai, K, Tosaki, T, Matsubayashi, K, Nakajima, T, Nishimura, Y, Tamura, Y
    The Astrophysical Journal 849 (2) 81:1 - 81:11 2017/11 [Refereed][Not invited]
  • OISTER Optical and Near-Infrared Monitoring Observations of a Peculiar Radio-Loud Active Galactic Nucleus SDSS J110006.07+442144.3
    Morokuma, T, Tanaka, M, Tanaka, Y. T, Itoh, R, Tominaga, N, Gandhi, P, Pian, E, Mazzali, P, Ohta, K, Matsumoto, E, Shibata, T, Akimoto, H, Akitaya, H, Ali, G. B, Aoki, T, Doi, M, Ebisuda, N, Essam, A, Fujisawa, K, Fukushima, H, Goda, S, Gouda, Y, Hanayama, H, Hashiba, Y, Hashimoto, O, Hayashida, K, Hiratsuka, Y, Honda, S, Imai, M, Inoue, K, Ishibashi, M, Iwata, I, Izumiura, H, Kanda, Y, Kawabata, M, Kawaguchi, K, Kawai, N, Kokubo, M, Kuroda, D, Maehara, H, Mito, H, Mitsuda, K, Miyagawa, R, Miyaji, T, Miyamoto, Y, Morihana, K, Moritani, Y, Morokuma-Matsui, K, Murakami, K, Murata, K. L, Nagayama, T, Nakamura, K, Nakaoka, T, Niinuma, K, Nishimori, T, Nogami, D, Oasa, Y, Oda, T, Ohshima, T, Saito, Y, Sakata, S, Sako, S, Sarugaku, Y, Sawada-Satoh, S, Seino, G, Sorai, K, Soyano, T, Taddia, F, Takahashi, J, Takagi, Y, Takaki, K, Takata, K, Tarusawa, K, Uemura, M, Ui, T, Urago, R, Ushioda, K, Watanabe, J, Watanabe, M, Yamashita, S, Yanagisawa, K, Yonekura, Y, Yoshida, M
    Publications of the Astronomical Society of Japan 69 (5) 82:1 - 82:20 2017/10 [Refereed][Not invited]
  • CO multi-line imaging of nearby galaxies (COMING) II: Transitions between atomic and molecular gas, diffuse and dense gas, gas and stars in the dwarf galaxy NGC 2976
    Hatakeyama, T, Kuno, N, Sorai, K, Kaneko, H, Miyamoto, Y, Muraoka, K, Takeda, M, Yanagitani, K, Kishida, N, Umei, M, Tanaka, T, Tomiyasu, Y, Nakanishi, H, Saita, C, Ueno, S, Salak, D, Matsumoto, N, Morokuma, K, Pan, H.-A, Nakai, N
    Publications of the Astronomical Society of Japan 69 (4) 67:1 - 67:14 2017/08 [Refereed][Not invited]
  • The 1.1 mm Continuum Survey of the Small Magellanic Cloud: Physical Properties and Evolution of the Dust-selected Clouds
    Takekoshi, T, Minamidani, T, Komugi, S, Kohno, K, Tosaki, T, Sorai, K, Muller, E, Mizuno, N, Kawamura, A, Onishi, T, Fukui, Y, Ezawa, H, Oshima, T, Scott, K.S, Austermann, J.E, Matsuo, H, Aretxaga, I, Hughes, D.H, Kawabe, R, Wilson, G.W, Yun, M.S
    The Astrophysical Journal 835 (1) 55:1 - 55:17 2017/01 [Refereed][Not invited]
  • Kazuhito Motogi, Kazuo Sorai, Mareki Honma, Tomoya Hirota, Kazuya Hachisuka, Kotaro Niinuma, Koichiro Sugiyama, Yoshinori Yonekura, Kenta Fujisawa
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 68 (5) 69:1 - 69:17 0004-6264 2016/10 [Refereed][Not invited]
     
    We report on long-term single-dish and VLBI monitoring for intermittent flare activities of a dominant blue-shifted H2O maser associated with a southern high mass young stellar object, G353.273+0.641. Bi-weekly single-dish monitoring using the Hokkaido University Tomakomai 11 m radio telescope has shown that a systematic acceleration continues over four years beyond the lifetime of individual maser features. This fact suggests that the H2O maser traces a region where molecular gas is steadily accelerated. There were five maser flares during the five years of monitoring, and maser distributions in four of them were densely monitored by VLBI Exploration of Radio Astrometry (VERA). The overall distribution of the maser features suggests the presence of a bipolar jet, with the 3D kinematics indicating that it is almost face-on (inclination angle of similar to 8 degrees-17 degrees from the line of sight). Most maser features were recurrently excited within a region of 100x100 au(2) around the radio continuum peak, while their spatial distributions significantly varied between each flare. This confirms that episodic propagations of outflow shocks recurrently invoke intermittent flare activities. We also measured annual parallax, deriving a source distance of 1.70(-0.16)(+0.19) kpc that is consistent with the commonly used photometric distance.
  • Koichiro Sugiyama, Kenta Fujisawa, Kazuya Hachisuka, Yoshinori Yonekura, Kazuhito Motogi, Satoko Sawada-Satoh, Naoko Matsumoto, Daiki Hirano, Kyonosuke Hayashi, Hideyuki Kobayashi, Noriyuki Kawaguchi, Katsunori M. Shibata, Mareki Honma, Tomoya Hirota, Yasuhiro Murata, Akihiro Doi, Hideo Ogawa, Kimihiro Kimura, Kotaro Niinuma, Xi Chen, Bo Xia, Bin Li, Kazuo Sorai, Munetake Momose, Yu Saito, Hiroshi Takaba, Toshihiro Omodaka, Kee-Tae Kim, Zhiqiang Shen
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 68 (5) 72:1 - 72:18 0004-6264 2016/10 [Refereed][Not invited]
     
    We detected internal proper motions of the methanol maser features at 6.7 GHz in a high-mass star-forming region G006.79-00.25 with the East-Asian VLBI Network. The spatial distribution of the maser features shows an elliptical morphology. The internal proper motions of 17 methanol maser features relative to the barycenter of the features were measured. The amplitude of the internal motions ranged from 1.30 to 10.25 kms(-1). Most of the internal proper motions of the maser features seem to point counter-clockwise along the elliptical morphology of the maser features. We applied the disk model, which includes both rotating and expanding components, to the observed positions, i.o.s. velocities, and proper motions. The derived rotation, expansion, and systemic velocities are +3(-2)(+2), +6(-2)(+2), and +21(-2)(+2) kms(-1), respectively, at the radius of 1260 au on the disk with a position angle of the semi-major axis of -140 degrees. and an inclination of 60 degrees. The derived rotating motion suggests that the methanol maser emissions showing the elliptical spatial morphology possibly trace the rotating disk. The derived expanding motion might be caused by the magnetic-centrifugal wind on the disk, which was estimated on the basis of the typical magnetic field strength at emitting zones of a methanol maser.
  • Yonekura, Y, Saito, Y, Sugiyama, K, Soon, K. L, Momose, M, Yokosawa, M, Ogawa, H, Kimura, K, Abe, Y, Nishimura, A, Hasegawa, Y, Fujisawa, K, Tomoaki, O, Kono, Y, Miyamoto, Y, Sawada-Satoh, S, Kobayashi, H, Kawaguchi, N, Honma, M, Shibata, K, Sato, K, Ueno, Y, Jike, T, Tamura, Y, Hirota, T, Miyazaki, A, Niinuma, K, Sorai, K, Takaba, H, Hachisuka, K, Kondo, T, Sekido, M, Murata, Y, Nakai, N, Omodaka, T
    Publications of the Astronomical Society of Japan 68 (5) 74:1 - 74:16 2016/10 [Refereed][Not invited]
  • Kazuyuki Muraoka, Kazuo Sorai, Nario Kuno, Naomasa Nakai, Hiroyuki Nakanishi, Miho Takeda, Kazuki Yanagitani, Hiroyuki Kaneko, Yusuke Miyamoto, Nozomi Kishida, Takuya Hatakeyama, Michiko Umei, Takahiro Tanaka, Yuto Tomiyasu, Chey Saita, Saeko Ueno, Naoko Matsumoto, Dragan Salak, Kana Morokuma-Matsui
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 68 (5) 89:1 - 89:14 0004-6264 2016/10 [Refereed][Not invited]
     
    We present simultaneous mappings of J = 1-0 emission of (CO)-C-12, (CO)-C-13, and (CO)-O-18 molecules toward the whole disk (8' x 5' or 20.8 kpc x 13.0 kpc) of the nearby barred spiral galaxy NGC 2903 with the Nobeyama Radio Observatory 45m telescope at an effective angular resolution of 20 '' (or 870 pc). We detected (CO)-C-12(J = 1-0)emission over the disk of NGC 2903. In addition, significant (CO)-C-13(J = 1-0) emission was found at the center and bar-ends, whereas we could not detect any significant (CO)-O-18(J = 1-0) emission. In order to improve the signal-to-noise ratio of CO emission and to obtain accurate line ratios of (CO)-C-12(J = 2-1)/(CO)-C-12(J = 1-0) (R2-1/1-0) and (CO)-C-13(J = 1-0)/(CO)-C-12(J = 1-0) (R-13/12), we performed the stacking analysis for our (CO)-C-12(J = 1-0), (CO)-C-13(J = 1-0), and archival (CO)-C-12(J = 2-1) spectra with velocity axis alignment in nine representative regions of NGC 2903. We successfully obtained the stacked spectra of the three CO lines, and could measure averaged R2-1/1-0 and R-13/12 with high significance for all the regions. We found that both R2-1/1-0 and R-13/12 differ according to the regions, which reflects the difference in the physical properties of molecular gas, i.e., density (n(H2)) and kinetic temperature (T-K). We determined n(H2) and T-K using R2-1/1-0 and R-13/12 based on the large velocity gradient approximation. The derived n(H2) ranges from similar to 1000 cm(-3) (in the bar, bar-ends, and spiral arms) to 3700 cm(-3) (at the center) and the derived T-K ranges from 10 K (in the bar and spiral arms) to 30 K (at the center). We examined the dependence of star formation efficiencies (SFEs) on n(H2) and T-K, and found a positive correlation between SFE and n(H2) with correlation coefficient for the least-squares power-law fit R-2 of 0.50. This suggests that molecular gas density governs the spatial variations in SFEs.
  • Kazuyuki Muraoka, Miho Takeda, Kazuki Yanagitani, Hiroyuki Kaneko, Kouichiro Nakanishi, Nario Kuno, Kazuo Sorai, Tomoka Tosaki, Kotaro Kohno
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 68 (2) 18:1 - 18:13 0004-6264 2016/04 [Refereed][Not invited]
     
    We present the results of CO(J= 3-2) on-the-fly mappings of two nearby non-barred spiral galaxies, NGC628 and NGC7793, with the Atacama Submillimeter Telescope Experiment at an effective angular resolution of 25 ''. We successfully obtained global distributions of CO(J = 3-2) emission over the entire disks at a sub-kpc resolution for both galaxies. We examined the spatially resolved (sub-kpc) relationship between CO(J = 3-2) luminosities (LCO(3-2)') and infrared (IR) luminosities (L-IR) for NGC628, NGC7793, and M83, and compared it with global luminosities of a JCMT (James Clerk Maxwell Telescope) Nearby Galaxy Legacy Survey sample. We found a striking linear L'(CO(3-2))-L-IR correlation over the four orders of magnitude, and the correlation is consistent even with that for ultraluminous IR galaxies and submillimeter-selected galaxies. In addition, we examined the spatially resolved relationship between CO(J = 3-2) intensities (ICO(3-2)) and extinctioncorrected star formation rates (SFRs) for NGC628, NGC7793, and M83, and compared it with that for Giant Molecular Clouds in M33 and 14 nearby galaxy centers. We found a linear ICO(3-2)-SFR correlation with similar to 1 dex scatter. We conclude that the CO(J = 3-2) star-formation law (i. e., linear L'(CO(3-2))-L-IR and ICO(3-2)-SFR correlations) is universally applicable to various types and spatial scales of galaxies; from spatially resolved nearby galaxy disks to distant IR-luminous galaxies, within similar to 1 dex scatter.
  • Yoshimasa Watanabe, Nami Sakai, Kazuo Sorai, Junko Ueda, Satoshi Yamamoto
    ASTROPHYSICAL JOURNAL 819 (2) 144:1 - 144:11 0004-637X 2016/03 [Refereed][Not invited]
     
    Molecular line images of (CO)-C-13, (CO)-O-18, CN, CS, CH3OH, and HNCO are obtained toward the spiral arm of M51 at a 7 '' x 6 '' resolution with the Combined Array for Research in Millimeter-wave Astronomy. Distributions of the molecules averaged over a 300 pc scale are found to be almost similar to one another and to essentially trace the spiral arm. However, the principal component analysis shows a slight difference of distributions among molecular species, particularly for CH3OH and HNCO. These two species do not correlate well with the star formation rate, implying that they are not enhanced by local star formation activities but by galactic-scale phenomena such as spiral shocks. Furthermore, the distributions of HNCO and CH3OH are found to be slightly different, and their origins deserve further investigation. The present results provide us with an important clue for. understanding the 300 pc scale chemical composition in the spiral arm and its relation to galactic-scale dynamics.
  • Hsi-An Pan, Nario Kuno, Jin Koda, Akihiko Hirota, Kazuo Sorai, Hiroyuki Kaneko
    ASTROPHYSICAL JOURNAL 815 (1) 59:1 - 59:14 0004-637X 2015/12 [Refereed][Not invited]
     
    In this work, we investigate the molecular gas and star-formation properties in the barred spiral galaxy NGC 6946 using multiple molecular lines and star-formation tracers. A high-resolution image (100 pc) of (CO)-C-13 (1-0) is created for the inner 2 kpc disk by the single-dish Nobeyama Radio Observatory 45 m telescope and interferometer Combined Array for Research in Millimeter-wave Astronomy, including the central region (nuclear ring and bar) and the offset ridges of the primary bar. Single-dish HCN (1-0) observations were also made to constrain the amount of dense gas. The physical properties of molecular gas are inferred from (1) the large velocity gradient calculations using our observations and archival (CO)-C-12 (1-0), (CO)-C-12(2-1) data, (2) the dense gas fraction suggested by the luminosity ratio of HCN to (CO)-C-12 (1-0), and (3) the infrared color. The results show that the molecular gas in the central region is warmer and denser than that of the offset ridges. The dense gas fraction of the central region is similar to that of luminous infrared galaxies/ultraluminous infrared galaxies, whereas the offset ridges are close to the global average of normal galaxies. The coolest and least-dense region is found in a spiral-like structure, which was misunderstood to be part of the southern primary bar in previous low-resolution observations. The star-formation efficiency (SFE) changes by about five times in the inner disk. The variation of SFE agrees with the prediction in terms of star formation regulated by the galactic bar. We find a consistency between the star-forming region and the temperature inferred by the infrared color, suggesting that the distribution of subkiloparsec-scale temperature is driven by star formation.
  • Hsi-An Pan, Nario Kuno, Kazuo Sorai, Michiko Umei
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 67 (6) 116:1 - 116:17 0004-6264 2015/12 [Refereed][Not invited]
     
    We used multi-wavelength analysis of the newly observed molecular gas [(CO)-C-12 and (CO)-C-13(1-0)] with interferometer CARMA and archival star formation tracers to constrain the interaction, merging, and star formation history of an off-center minor merger, a three-spiral barred galaxy NGC5430 and its satellite embedded in the bar. Morphology of the molecular gas in the bar of NGC5430 shows minimal signs of recent interactions with our resolution. The apparent morphological remnant of the past galaxy interaction is an asymmetric spiral arm, containing more molecular gas and exhibiting higher star formation rate (SFR) surface density than the two primary arms. Rotation curve analysis suggests that NGC5430 collided with its satellite several Gyr ago. History of star formation was constrained by using SFRs that trace different timescales (infrared, radio continuum, and Ha). The collision occurred 5-10 Myr ago, triggering a transient off-center starburst of Wolf-Rayet stars at the eastern bar end. In the past, the global SFR during the Wolf-Rayet starburst peaked at 35M(circle dot)yr(-1). At present, the merger-driven starburst is rapidly decaying and the current global SFR has decreased to the Galactic value. The SFR will continue to decay as suggested by the present amount of dense gas [traced by HCN(1-0)]. Nonetheless, the global SFR is still dominated by the Wolf-Rayet region rather than the circumnuclear region. Compared with other barred galaxies, the circumnuclear region exhibits a particularly low dense gas fraction, low star formation activity, and high concentration of gas. Physical properties of the molecular gas are inferred by using the large velocity gradient calculations. The initial mass ratio of NGC5430 to its satellite is suggested to be in an intermediate ratio range of 7: 1-20: 1.
  • Kana Morokuma-Matsui, Junichi Baba, Kazuo Sorai, Nario Kuno
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 67 (3) 36:1 - 36:13 0004-6264 2015/06 [Refereed][Not invited]
     
    We performed (CO)-C-12(J = 1-0) (hereafter, CO) observations toward 12 normal star-forming galaxies with stellar masses of M-star = 10(10.6)-10(11.3) M-circle dot at z = 0.1-0.2 with the 45 m telescope at the Nobeyama Radio Observatory. The samples were selected with D-n(4000), that is, the strength of the 4000 angstrom break, instead of the commonly used far-infrared (FIR) flux. We successfully detected the CO emissions from eight galaxies with signal-to-noise ratio larger than three, demonstrating the effectiveness of the D-n(4000)-based sample selection. For the first time, we find a tight anti-correlation between D-n(4000) and molecular gas fraction (f(mol)) using literature data of nearby galaxies in which the galaxies with more fuel for star formation have younger stellar populations. We find that our CO-detected galaxies at z similar to 0.1-0.2 also follow the same relation as nearby galaxies. This implies that the galaxies evolve along this D-n(4000)-f(mol) relation, and that D-n(4000) seems to be able to be used as a proxy for fmol, which requires many time-consuming observations. Based on the comparison with the model calculation with a population synthesis code, we find that star formation from metal enriched gas and its quenching in the early time are necessary to reproduce galaxies with large D-n(4000) and non-zero gas fraction.
  • Stacking Analysis of 12CO and 13CO Spectra of NGC3627: Existence of non-optically thick 12CO emission?
    Morokuma-Matsui, K, Sorai, K, Watanabe, Y, Kuno, N
    Publications of the Astronomical Society of Japan 67 (1) 2:1 - 2:17 2015/02 [Refereed][Not invited]
  • VLBI observations of bright AGN jets with KVN and VERA Array (KaVA): Evaluation of Imaging Capability
    Niinuma, K, Lee, S.-S, Kino, M, Sohn, B. W, Akiyama, K, Zhao, G.-Y, Sawada-Satoh, S, Trippe, S, Hada, K, Jung, T, Hagiwara, Y, Dodson, R, Koyama, S, Honma, M, Nagai, H, Chung, A, Doi, A, Fujisawa, K, Han, M.-H, Kim, J.-S, Lee, J, Lee, J. A, Miyazaki, A, Oyama, T, Sorai, K, Wajima, K, Bae, J, Byun, D.-Y, Cho, S.-H, Choi, Y. K, Chung, H, Chung, M.-H, Han, S.-T, Hirota, T, Hwang, J.-W, Je, D.-H, Jike, T, Jung, D.-K, Jung, J.-S, Kang, J.-H, Kang, J, Kang, Y.-W, Kan-ya, Y, Kanaguchi, M, Kawaguchi, N, Kim, B. G, Ryoung Kim, H, Kim, H.-G, Kim, J, Kim, J, Kim, K.-T, Kim, M, Kobayashi, H, Kono, Y, Kurayama, T, Lee, C., Lee, J.-W, Lee, S. H, Minh, Y. C, Matsumoto, N, Nakagawa, A., Oh, C. S., Oh, S.-J., Park, S.-Y, Roh, D.-G, Sasao, T, Shibata, K. M, Song, M.-G, Tamura, Y., Wi, S.-O., Yeom, J.-H, Yun, Y. J
    Publications of the Astronomical Society of Japan 66 (6) 103:1 - 103:16 2014/12 [Refereed][Not invited]
  • Spectral Line Survey toward Spiral Arm of M51 in the 3 mm and 2 mm Bands
    Watanabe, Y, Sakai, N, Sorai, K, Yamamoto, S
    The Astrophysical Journal 788 (1) 4:1 - 4:20 2014/06 [Refereed][Not invited]
  • Fujisawa, K, Sugiyama, K, Motogi, K, Hachisuka, K, Yonekura, Y, Sawada-Satoh, S, Matsumoto, N, Sorai, K, Momose, M, Saito, Y, Takaba, H, Ogawa, H, Kimura, K, Niinuma, K, Hirano, D, Omodaka, T, Kobayashi, H, Kawaguchi, N, Shibata, K. M, Honma, M, Hirota, T, Murata, Y, Doi, A, Mochizuki, N, Shen, Z, Chen, X, Xia, B, Li, B, Kim, K.-T
    Publications of the Astronomical Society of Japan 66 (2) 31:1 - 31:29 2014/02 [Refereed][Not invited]
  • Tatsuya Takekoshi, Yoichi Tamura, Tetsuhiro Minamidani, Kotaro Kohno, Taira Oogi, Kazuo Sorai, Asao Habe, Hajime Ezawa, Tai Oshima, Kimberly S. Scott, Jason E. Austermann, Shinya Komugi, Tomoka Tosaki, Norikazu Mizuno, Erik Muller, Akiko Kawamura, Toshikazu Onishi, Yasuo Fukui, Hiroshi Matsuo, Itziar Aretxaga, David H. Hughes, Ryohei Kawabe, Grant W. Wilson, Min S. Yun
    The Astrophysical Journal Letters 774 (2) L30:1 - L30:6 2013/08/29 [Refereed][Not invited]
     
    We report the discovery of a new ultra-bright submillimeter galaxy (SMG) behind the Small Magellanic Cloud (SMC). This SMG is detected as a 43.3+-8.4 mJy point source (MM J01071-7302, hereafter MMJ0107) in the 1.1 mm continuum survey of the SMC by AzTEC on the ASTE telescope. MMJ0107 is also detected in the radio (843 MHz), Herschel/SPIRE, Spitzer MIPS 24 {\mu}m, all IRAC bands, Wide-field Infrared Survey Explorer, and near-infrared (J, H, KS). We find an optical (U, B, V) source, which might be the lensing object, at a distance of 1.4 arcsec from near-infrared and IRAC sources. Photometric redshift estimates for the SMG using representative spectral energy distribution templates show the redshifts of 1.4-3.9. We estimate total far-infrared luminosity of (0.3-2.2)x10^14 {\mu}^-1 L_sun and a star formation rate of 5600-39, 000 {\mu}^-1 M_sun yr^-1, where {\mu} is the gravitational magnification factor. This apparent extreme star formation activity is likely explained by a highly magnified gravitational lens system.
  • GENJI Programme: Gamma-ray Emitting Notable AGN Monitoring by Japanese VLBI
    Nagai, H, Kino, M, Niinuma, K, Akiyama, K, Hada, K, Koyama, S, Orienti, M, Hiura, K, Sawada-Satoh, S, Honma, M, Giovannini, G, Giroletti, M, Shibata, K, Sorai, K
    Publications of the Astronomical Society of Japan 65 (2) 24:1 - 24:14 2013/04 [Refereed][Not invited]
  • Akihiro Doi, Kotaro Kohno, Kouichiro Nakanishi, Seiji Kameno, Makoto Inoue, Kazuhiro Hada, Kazuo Sorai
    Astrophysical Journal 765 (1) 63:1 - 63:11 1538-4357 2013/03/01 [Refereed][Not invited]
     
    The nearby low-luminosity active galactic nucleus (LLAGN) NGC 4258 has a weak radio continuum component at the galactic center. We investigate its radio spectral properties on the basis of our new observations using the Nobeyama Millimeter Array at 100 GHz and archival data from the Very Large Array at 1.7-43 GHz and the James Clerk Maxwell telescope at 347 GHz. The NGC 4258 nuclear component exhibits (1) an intra-month variable and complicated spectral feature at 5-22 GHz and (2) a slightly inverted spectrum at 5-100 GHz (α ∼ 0.3 F ν∝να) in time-averaged flux densities, which are also apparent in the closest LLAGN M81. These similarities between NGC 4258 and M81 in radio spectral natures in addition to previously known core shift in their AU-scale jet structures produce evidence that the same mechanism drives their nuclei. We interpret the observed spectral property as the superposition of emission spectra originating at different locations with frequency-dependent opacity along the nuclear jet. Quantitative differences between NGC 4258 and M81 in terms of jet/counter jet ratio, radio loudness, and degree of core shift can be consistently understood by fairly relativistic speeds (Γ ≳ 3) of jets and their quite different inclinations. The picture established from the two closest LLAGNs is useful for understanding the physical origin of unresolved and flat/inverted spectrum radio cores that are prevalently found in LLAGNs, including Sgr A*, with starved supermassive black holes in the present-day universe. © 2013. The American Astronomical Society. All rights reserved.
  • M. Nimori, A. Habe, K. Sorai, Y. Watanabe, A. Hirota, D. Namekata
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 429 (3) 2175 - 2182 0035-8711 2013/03 [Refereed][Not invited]
     
    We investigate the properties of massive, dense clouds formed in a barred galaxy and their possible relation to star formation, performing a two-dimensional hydrodynamical simulation with the gravitational potential obtained from the 2MASS data from the barred spiral galaxy, M83. Since the environment for cloud formation and evolution in the bar region is expected to be different from that in the spiral arm region, barred galaxies are a good target to study the environmental effects on cloud formation and the subsequent star formation. Our simulation uses for an initial 80 Myr isothermal flow of non-self gravitating gas in the barred potential, then including radiative cooling, heating and self-gravitation of the gas for the next 40 Myr, during which dense clumps are formed. We identify many cold, dense gas clumps for which the mass is more than 10(4) M-circle dot (a value corresponding to the molecular clouds) and study the physical properties of these clumps. The relation of the velocity dispersion of the identified clump's internal motion with the clump size is similar to that observed in the molecular clouds of our Galaxy. We find that the virial parameters for clumps in the bar region are larger than that in the spiral arm region. From our numerical results, we estimate star formation in the bar and spiral arm regions by applying the simple model of Krumholz & McKee (2005). The mean relation between star formation rate and gas surface density agrees well with the observed Kennicutt-Schmidt relation. The star formation efficiency in the bar region is similar to 60 per cent of the spiral arm region. This trend is consistent with observations of barred galaxies.
  • K. Motogi, K. Sorai, K. Niinuma, K. Sugiyama, M. Honma, K. Fujisawa
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 428 (1) 349 - 353 0035-8711 2013/01 [Refereed][Not invited]
     
    We report the first detection of a radio continuum and molecular jet associated with a dominant blue-shifted maser source, G353.273+0.641. A radio jet is extended 3000 au along the north-west-south-east (NW-SE) direction. H2O masers are found to be clustered in the root of a bipolar radio jet. A molecular jet is detected by thermal SiO (upsilon = 0, J = 2-1) emission. The SiO spectrum is extremely wide (-120 to +87 km s(-1)) and significantly blue-shift dominated, similar to the maser emission. The observed geometry and remarkable spectral similarity between H2O maser and SiO strongly suggest the existence of a maser-scale (similar to 340 au) molecular jet that is enclosed by the extended radio jet. We propose a disc-masking scenario as the origin of the strong blue-shift dominance, where an optically thick disc obscures a red-shifted lobe of a compact jet.

MISC

  • Kazuyuki Muraoka, Kotaro Kohno, Tomoka Tosaki, Nario Kuno, Kouichiro Nakanishi, Kazuo Sorai, Tsuyoshi Sawada, Kunihiko Tanaka, Toshihiro Handa, Masayuki Fukuhara, Hajime Ezawa, Ryohei Kawabe  ASTROPHYSICAL JOURNAL  706-  (2)  1213  -1225  2009/12  [Not refereed][Not invited]
     
    We present a new on-the-fly mapping of CO (J = 3-2) line emission with the Atacama Submillimeter Telescope Experiment toward the 8' x 8' (or 10.5 x 10.5 kpc at the distance of 4.5 Mpc) region of the nearby barred spiral galaxy M83 at an effective resolution of 25 ''. Due to its very high sensitivity, our CO (J = 3-2) map can depict not only spiral arm structures but also spur-like substructures extended in inter-arm regions. This spur-like substructures in CO (J = 3-2) emission are well coincident with the distribution of massive star-forming regions traced by H alpha luminosity and Spitzer/Infrared Array Camera 8 mu m emission. We have identified 54 CO (J = 3-2) clumps as Giant Molecular-cloud Associations (GMAs) employing the CLUMPFIND algorithm, and have obtained their sizes, velocity dispersions, virial masses, and CO luminosity masses. We found that the virial parameter alpha, which is defined as the ratio of the virial mass to the CO luminosity mass, is almost unity for GMAs in spiral arms, whereas there exist some GMAs whose alpha are 3-10 in the inter-arm region. We found that GMAs with higher alpha tend not to be associated with massive star-forming regions, while other virialized GMAs are. Since alpha mainly depends on velocity dispersion of the GMA, we suppose that the onset of star formation in these unvirialized GMAs with higher alpha are suppressed by an increase in internal velocity dispersions of giant molecular clouds within these GMAs due to shear motion.
  • Akihiro Doi, Noriyuki Kawaguchi, Yusuke Kono, Tomoaki Oyama, Kenta Fujisawa, Hiroshi Takaba, Hiroshi Sudou, Ken-ichi Wakamatsu, Aya Yamauchi, Yasuhiro Murata, Nanako Mochizuki, Kiyoaki Wajima, Toshihiro Omodaka, Takumi Nagayama, Naomasa Nakai, Kazuo Sorai, Eiji Kawai, Mamoru Sekido, Yasuhiro Koyama, Shoichiro Asano, Hisao Uose  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  61-  (6)  1389  -1398  2009/12  [Not refereed][Not invited]
     
    We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network. We aimed to select BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of the quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10(5) K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources, or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars.
  • Kazuyuki Muraoka, Kotaro Kohno, Tomoka Tosaki, Nario Kuno, Kouichiro Nakanishi, Kazuo Sorai, Tsuyoshi Sawada, Kunihiko Tanaka, Toshihiro Handa, Masayuki Fukuhara, Hajime Ezawa, Ryohei Kawabe  ASTROPHYSICAL JOURNAL  706-  (2)  1213  -1225  2009/12  [Not refereed][Not invited]
     
    We present a new on-the-fly mapping of CO (J = 3-2) line emission with the Atacama Submillimeter Telescope Experiment toward the 8' x 8' (or 10.5 x 10.5 kpc at the distance of 4.5 Mpc) region of the nearby barred spiral galaxy M83 at an effective resolution of 25 ''. Due to its very high sensitivity, our CO (J = 3-2) map can depict not only spiral arm structures but also spur-like substructures extended in inter-arm regions. This spur-like substructures in CO (J = 3-2) emission are well coincident with the distribution of massive star-forming regions traced by H alpha luminosity and Spitzer/Infrared Array Camera 8 mu m emission. We have identified 54 CO (J = 3-2) clumps as Giant Molecular-cloud Associations (GMAs) employing the CLUMPFIND algorithm, and have obtained their sizes, velocity dispersions, virial masses, and CO luminosity masses. We found that the virial parameter alpha, which is defined as the ratio of the virial mass to the CO luminosity mass, is almost unity for GMAs in spiral arms, whereas there exist some GMAs whose alpha are 3-10 in the inter-arm region. We found that GMAs with higher alpha tend not to be associated with massive star-forming regions, while other virialized GMAs are. Since alpha mainly depends on velocity dispersion of the GMA, we suppose that the onset of star formation in these unvirialized GMAs with higher alpha are suppressed by an increase in internal velocity dispersions of giant molecular clouds within these GMAs due to shear motion.
  • Akihiro Doi, Noriyuki Kawaguchi, Yusuke Kono, Tomoaki Oyama, Kenta Fujisawa, Hiroshi Takaba, Hiroshi Sudou, Ken-ichi Wakamatsu, Aya Yamauchi, Yasuhiro Murata, Nanako Mochizuki, Kiyoaki Wajima, Toshihiro Omodaka, Takumi Nagayama, Naomasa Nakai, Kazuo Sorai, Eiji Kawai, Mamoru Sekido, Yasuhiro Koyama, Shoichiro Asano, Hisao Uose  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  61-  (6)  1389  -1398  2009/12  [Not refereed][Not invited]
     
    We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network. We aimed to select BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of the quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10(5) K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources, or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars.
  • Akihiko Hirota, Nario Kuno, N. Sato, Hiroyuki Nakanishi, Tomoka Tosaki, Hidenori Matsui, Asao Habe, Kazuo Sorai  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  61-  (3)  441  -450  2009/06  [Not refereed][Not invited]
     
    We evaluated the availability of a method proposed by Kuno et al. (2000, PASJ, 52, 775) for measuring the pattern speed of barred galaxies, and applied it to observational data. We made error estimations using a hydrodynamical galaxy model to test the validity of the method. Error estimations suggest that the method is able to determine the pattern speed within an error of 10%-20%. The method was applied to (CO)-C-12 (1-0) data of three late-type barred galaxies: NGC 2903, M 83, and NGC 3627. The derived pattern speed was 40 km s(-1) kpc(-1) for NGC 2903, 57 km s(-1) kpc(-1) for M 83, 39 km s(-1) kpc(-1) for NGC 3627, respectively. For the sake of a comparison with measurements in other galaxies, we used the distance-independent value R (equivalent to R-CR/R-bar), and found that bars in the three late-type spirals are "slow" (R > 1.4). Our results support recent claims that bars are not always "fast" (R <= 1.4), at least for late-type spiral galaxies.
  • Akihiko Hirota, Nario Kuno, N. Sato, Hiroyuki Nakanishi, Tomoka Tosaki, Hidenori Matsui, Asao Habe, Kazuo Sorai  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  61-  (3)  441  -450  2009/06  [Not refereed][Not invited]
     
    We evaluated the availability of a method proposed by Kuno et al. (2000, PASJ, 52, 775) for measuring the pattern speed of barred galaxies, and applied it to observational data. We made error estimations using a hydrodynamical galaxy model to test the validity of the method. Error estimations suggest that the method is able to determine the pattern speed within an error of 10%-20%. The method was applied to (CO)-C-12 (1-0) data of three late-type barred galaxies: NGC 2903, M 83, and NGC 3627. The derived pattern speed was 40 km s(-1) kpc(-1) for NGC 2903, 57 km s(-1) kpc(-1) for M 83, 39 km s(-1) kpc(-1) for NGC 3627, respectively. For the sake of a comparison with measurements in other galaxies, we used the distance-independent value R (equivalent to R-CR/R-bar), and found that bars in the three late-type spirals are "slow" (R > 1.4). Our results support recent claims that bars are not always "fast" (R <= 1.4), at least for late-type spiral galaxies.
  • Kazuyuki Muraoka, Kotaro Kohno, Tomoka Tosaki, Nario Kuno, Kouichiro Nakanishi, Toshihiro Handa, Kazuo Sorai, Sumio Ishizuki, Takeshi Okuda  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  61-  (2)  163  -176  2009/04  [Not refereed][Not invited]
     
    We present aperture synthesis high-resolution (similar to 7 '' x 3 '') observations in CO (J = 1-0), HCN (J = 1-0), and 95 GHz Continuum emission toward the central (similar to 1.5 kpc) region of the nearby barred spiral galaxy M 83 with the Nobeyama Millimeter Array. Our high-resolution CO (J = 1-0) mosaic map depicts the presence of molecular ridges along the leading sides of the stellar bar and a nuclear twin peak structure, whereas the distributions of the HCN (J = 1-0) emission that traces dense molecular gas (n(H2) > a few x 10(4) cm(-3)) and the 95 GHz continuum emission that traces massive starburst show nuclear single-peak structures. The HCN (J = 1-0) and the 95 GHz continuum peaks are not spatially coincident with file optical starburst regions traced by the HST V-band image, suggesting the existence of deeply buried ongoing starburst due to strong extinction (A(V) similar to 5 map) near these peaks. We found that the HCN (J = 1-0)/CO (J = 1-0) intensity ratio, R-HCN/CO, correlates well with the extinction-corrected star formation efficiency (SFE) in the central region of M 83 at a resolution of 7.'' 5 (similar to 160 pc). This suggests that SFE is controlled by it dense gas fraction traced by R-HCN/CO, even on a Giant Molecular cloud Association (GMA) scale. Moreover, the correlation between R-HCN/CO and SFE in M 83 seems to be almost coincident with that among the Gao and Solomon (2004a, ApJ, 606, 271) sample. This Suggests that the correlation between R-HCN/CO and the SFE on a GMA (similar to 160pc) scale found in M 83 is the origin ofthe global correlation on a few kpc scale shown by Gao and Solomon (2004a).
  • Nobeyama Millimeter Array Observations of the Nuclear Starburst of M 83: A GMA Scale Correlation between Dense Gas Fraction and Star Formation Efficiency
    Muraoka, K, Kohno, K, Tosaki, T, Kuno, N, Nakanishi, K, Handa, T, Sorai, K, Ishizuki, S, Okuda, T  Publications of the Astronomical Society of Japan  61-  (2)  163–176  2009  [Not refereed][Not invited]
  • Kazuo Sorai, Asao Habe, Hiroyuki Nishitani, Keita Hosaka, Yoshimasa Watanabe, Shinichi Miwa, Yukie Ohishi, Kazuhito Motogi, Tetsuhiro Minamidani, Johta Awano, Sakurako Sumida, Yoshiaki Fukuya, Ryosuke Uchida, Noboru Kaneko, Masayuki Y. Fujimoto, Yasuhiro Koyama, Moritaka Kimura, Naomasa Nakai  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  60-  (6)  1285  -1296  2008/12  [Not refereed][Not invited]
     
    Large-area observations of dense molecular gas were made in NH3 (J, K) = (1, 1), (2, 2), and (3, 3) inversion lines with 4'.5 resolution toward the molecular cloud complex of the W 51 region. The observations were a part of a NH3 survey of the Galactic star-forming regions using the Tomakorrai 11-m radio telescope. NH3 (J, K) = (1, 1) and (2, 2) emission was detected in the W51 A and B complexes, while the detection of (J, K) = (2, 2) emission was marginal in W 51 B. The rotation temperature was similar to 40 K in the central part of the W 51 A complex, while being similar to 20 K in the other positions. A weak correlation is found that the ortho-to-para ratio decreases with increasing the rotation temperature, the far-infrared luminosity and the index of the star-formation efficiency. This tendency is explained if star formation has continued for more than the time scale of the transformation between ortho- and para-NH3: active star formation on a large scale, such as the interaction of molecular clouds with a spiral arm, has made the molecular gas warmer, even in a scale of similar to 10 pc, and the proceeding transformation has made the ortho-to-para ratio lower.
  • Kazuo Sorai, Asao Habe, Hiroyuki Nishitani, Keita Hosaka, Yoshimasa Watanabe, Shinichi Miwa, Yukie Ohishi, Kazuhito Motogi, Tetsuhiro Minamidani, Johta Awano, Sakurako Sumida, Yoshiaki Fukuya, Ryosuke Uchida, Noboru Kaneko, Masayuki Y. Fujimoto, Yasuhiro Koyama, Moritaka Kimura, Naomasa Nakai  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  60-  (6)  1285  -1296  2008/12  [Not refereed][Not invited]
     
    Large-area observations of dense molecular gas were made in NH3 (J, K) = (1, 1), (2, 2), and (3, 3) inversion lines with 4'.5 resolution toward the molecular cloud complex of the W 51 region. The observations were a part of a NH3 survey of the Galactic star-forming regions using the Tomakorrai 11-m radio telescope. NH3 (J, K) = (1, 1) and (2, 2) emission was detected in the W51 A and B complexes, while the detection of (J, K) = (2, 2) emission was marginal in W 51 B. The rotation temperature was similar to 40 K in the central part of the W 51 A complex, while being similar to 20 K in the other positions. A weak correlation is found that the ortho-to-para ratio decreases with increasing the rotation temperature, the far-infrared luminosity and the index of the star-formation efficiency. This tendency is explained if star formation has continued for more than the time scale of the transformation between ortho- and para-NH3: active star formation on a large scale, such as the interaction of molecular clouds with a spiral arm, has made the molecular gas warmer, even in a scale of similar to 10 pc, and the proceeding transformation has made the ortho-to-para ratio lower.
  • K. Motogi, Y. Watanabe, K. Sorai, A. Habe, M. Honma, H. Imai, A. Yamauchi, H. Kobayashi, K. Fujisawa, T. Omodaka, H. Takaba, K. M. Shibata, T. Minamidani, K. Wakamatsu, H. Sudou, E. Kawai, Y. Koyama  MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY  390-  (2)  523  -534  2008/10  [Not refereed][Not invited]
     
    We have made multi-epoch very long baseline interferometer (VLBI) observations of H2O maser emission in the massive star-forming region IRAS 06061+2151 with the Japanese VLBI network (JVN) from 2005 May to 2007 October. The detected maser features are distributed within a 1 x 1 arcsec(2) area (2000 x 2000 au(2) at the source position) around the ultracompact H II region seen in radio continuum emission. The bipolar morphology and expanding motion traced through their relative proper motions indicate that they are excited by an energetic bipolar outflow. Our three-dimensional model fitting has shown that the maser kinematical structure in IRAS 06061+2151 can be explained by a biconical outflow with a large opening angle (> 50 degrees). The position angle of the flow major axis coincides very well with that of the large-scale jet seen in 2.1 mu m hydrogen emission. This maser geometry indicates the existence of dual structures composed of a collimated jet and a less collimated massive molecular flow. We have also detected a large velocity gradient in the southern maser group. This can be explained by a very small (on a scale of several tens of astronomical units) and clumpy (the density contrast by an order of magnitude or more) structure of the parental cloud. Such a structure may be formed by strong instability of the shock front or splitting of the high density core.
  • Takumi Nagayama, Koji Takeda, Toshihiro Omodaka, Hiroshi Imai, Seiji Kameno, Yoshiaki Sofue, Akihiro Doi, Kenta Fujisawa, Asao Habe, Mareki Honma, Noriyuki Kawaguchi, Eiji Kawai, Hideyuki Kobayashi, Yasuhiro Koyama, Yasuhiro Murata, Kazuo Sorai, Hiroshi Sudou, Hiroshi Takaba, Sayaka Tamura, Ken-ichi Wakamatsu  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  60-  (5)  1069  -1075  2008/10  [Not refereed][Not invited]
     
    We present the proper motions of H2O masers in NML Cygni, observed with the Japanese VLBI Network at three epochs spanning 455 d. We detected about 15 maser features at each epoch. Overall, 13 features that were detected at least twice were tracked by their radial velocities and proper motions. The three-dimensional kinematics of the maser features indicate the presence of an expanding outflow. The major axis of the outflow is estimated to be at a position angle of similar to 108 degrees, and an inclination angle of similar to 8 degrees with respect to the line of sight. The H2O masers are located between an apparent minimum radius of similar to 9.6 x 10(12) m (64 AU) and a maximum radius of similar to 3.0 x 10(13) m (202 AU), where the expansion velocity increases from 12 to 27 km s(-1). A comparison with the distributions of SiO, H2O, and OH masers suggests that the outflow of NML Cygni is expanding outside a radius of similar to 1.5 x 10(13) m 100 AU. This radius corresponds to 6 stellar radii, and is consistent with the radius of the inner boundary for the dust shell.
  • Takuma Suda, Yutaka Katsuta, Shimako Yamada, Tamon Suwa, Chikako Ishizuka, Yutaka Komiya, Kazuo Sorai, Masayuki Aikawa, Masayuki Y. Fujimoto  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  60-  (5)  1159  -1171  2008/10  [Not refereed][Not invited]
     
    We describe the construction of a database of extremely metal-poor (EMP) stars in the Galaxy. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the literature that report on studies of EIMP halo stars with [Fe/H] <= -2.5. The compilation procedures for this database were designed to assemble data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria and illustrations to explore relationships between stored variables. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering relevant papers published by 2007 December. We discus; the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe/H] <= -2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amounts to similar to 30% for [Fe/H] <= -2.5. We find that known binaries exhibit different distributions of the orbital period, according to wiether they are giants or dwarfs,, and also as a function of the metallicity, although the total sample of such stars is still quite small.
  • K. Motogi, Y. Watanabe, K. Sorai, A. Habe, M. Honma, H. Imai, A. Yamauchi, H. Kobayashi, K. Fujisawa, T. Omodaka, H. Takaba, K. M. Shibata, T. Minamidani, K. Wakamatsu, H. Sudou, E. Kawai, Y. Koyama  MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY  390-  (2)  523  -534  2008/10  [Not refereed][Not invited]
     
    We have made multi-epoch very long baseline interferometer (VLBI) observations of H2O maser emission in the massive star-forming region IRAS 06061+2151 with the Japanese VLBI network (JVN) from 2005 May to 2007 October. The detected maser features are distributed within a 1 x 1 arcsec(2) area (2000 x 2000 au(2) at the source position) around the ultracompact H II region seen in radio continuum emission. The bipolar morphology and expanding motion traced through their relative proper motions indicate that they are excited by an energetic bipolar outflow. Our three-dimensional model fitting has shown that the maser kinematical structure in IRAS 06061+2151 can be explained by a biconical outflow with a large opening angle (> 50 degrees). The position angle of the flow major axis coincides very well with that of the large-scale jet seen in 2.1 mu m hydrogen emission. This maser geometry indicates the existence of dual structures composed of a collimated jet and a less collimated massive molecular flow. We have also detected a large velocity gradient in the southern maser group. This can be explained by a very small (on a scale of several tens of astronomical units) and clumpy (the density contrast by an order of magnitude or more) structure of the parental cloud. Such a structure may be formed by strong instability of the shock front or splitting of the high density core.
  • Takumi Nagayama, Koji Takeda, Toshihiro Omodaka, Hiroshi Imai, Seiji Kameno, Yoshiaki Sofue, Akihiro Doi, Kenta Fujisawa, Asao Habe, Mareki Honma, Noriyuki Kawaguchi, Eiji Kawai, Hideyuki Kobayashi, Yasuhiro Koyama, Yasuhiro Murata, Kazuo Sorai, Hiroshi Sudou, Hiroshi Takaba, Sayaka Tamura, Ken-ichi Wakamatsu  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  60-  (5)  1069  -1075  2008/10  [Not refereed][Not invited]
     
    We present the proper motions of H2O masers in NML Cygni, observed with the Japanese VLBI Network at three epochs spanning 455 d. We detected about 15 maser features at each epoch. Overall, 13 features that were detected at least twice were tracked by their radial velocities and proper motions. The three-dimensional kinematics of the maser features indicate the presence of an expanding outflow. The major axis of the outflow is estimated to be at a position angle of similar to 108 degrees, and an inclination angle of similar to 8 degrees with respect to the line of sight. The H2O masers are located between an apparent minimum radius of similar to 9.6 x 10(12) m (64 AU) and a maximum radius of similar to 3.0 x 10(13) m (202 AU), where the expansion velocity increases from 12 to 27 km s(-1). A comparison with the distributions of SiO, H2O, and OH masers suggests that the outflow of NML Cygni is expanding outside a radius of similar to 1.5 x 10(13) m 100 AU. This radius corresponds to 6 stellar radii, and is consistent with the radius of the inner boundary for the dust shell.
  • Takuma Suda, Yutaka Katsuta, Shimako Yamada, Tamon Suwa, Chikako Ishizuka, Yutaka Komiya, Kazuo Sorai, Masayuki Aikawa, Masayuki Y. Fujimoto  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  60-  (5)  1159  -1171  2008/10  [Not refereed][Not invited]
     
    We describe the construction of a database of extremely metal-poor (EMP) stars in the Galaxy. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the literature that report on studies of EIMP halo stars with [Fe/H] <= -2.5. The compilation procedures for this database were designed to assemble data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria and illustrations to explore relationships between stored variables. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering relevant papers published by 2007 December. We discus; the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe/H] <= -2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amounts to similar to 30% for [Fe/H] <= -2.5. We find that known binaries exhibit different distributions of the orbital period, according to wiether they are giants or dwarfs,, and also as a function of the metallicity, although the total sample of such stars is still quite small.
  • KOHNO Kotaro, TOSAKI Tomoka, MIURA Rie, MURAOKA Kazuyuki, SAWADA Tsuyoshi, NAKANISHI Kouichiro, KUNO Nario, SAKAI Takeshi, SORAI Kazuo, KAMEGAI Kazuhisa, TANAKA Kunihiko, OKUDA Takeshi, ENDO Akira, HATSUKADE Bunyo, SAMESHIMA Masahiro, EZAWA Hajime, SAKAMOTO Seiichi, KAMAZAKI Takeshi, YAMAGUCHI Nobuyuki, CORTES Juan, TAMURA Yoichi, FUKUHARA Masayuki, IONO Daisuke, KAWABE Ryohei  Publications of the Astronomical Society of Japan  60-  (3)  457  -464  2008/06/25  [Not refereed][Not invited]
  • KOHNO Kotaro, TOSAKI Tomoka, MIURA Rie, MURAOKA Kazuyuki, SAWADA Tsuyoshi, NAKANISHI Kouichiro, KUNO Nario, SAKAI Takeshi, SORAI Kazuo, KAMEGAI Kazuhisa, TANAKA Kunihiko, OKUDA Takeshi, ENDO Akira, HATSUKADE Bunyo, SAMESHIMA Masahiro, EZAWA Hajime, SAKAMOTO Seiichi, KAMAZAKI Takeshi, YAMAGUCHI Nobuyuki, CORTES Juan, TAMURA Yoichi, FUKUHARA Masayuki, IONO Daisuke, KAWABE Ryohei  Publications of the Astronomical Society of Japan  60-  (3)  457  -464  2008/06/25  [Not refereed][Not invited]
  • Nario Kuno, Kouichiro Nakanishi, Kazuo Sorai, Toshihito Shibatsuka  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  60-  (3)  475  -485  2008/06  [Not refereed][Not invited]
     
    The distribution and kinematics of molecular gas in the central region of the barred spiral galaxy Maffei 2 were investigated using a data set of (CO)-C-12 (1-0), (CO)-C-12 (2-1), CS (2-1) lines, and 103 GHz continuum. We found that the offset ridges along the kpc-scale bar continue to the central spiral structure embedded in a weak oval structure, which is regarded as an x2 orbit in the bar potential. The spiral structure continues toward the center, diverging from the oval structure. The size of these structures is less than R similar to 100 pc. The mass concentration within R = 35 pc is estimated to be 2 x 10(8) M-circle dot. The high mass concentration is consistent with theoretical predictions concerning the creation of such a nuclear spiral structure. A comparison with tracers of dense gas and star-forming region suggests that the dense molecular gas traced by the CS (2-1) line is formed at the crossing points of the x1 and x2 orbits and the star-forming region appears after 2 x 10(5) yr, which is comparable to the free-fall time of dense gas traced by the CS line (similar to 10(5) cm(-3)).
  • Nario Kuno, Kouichiro Nakanishi, Kazuo Sorai, Toshihito Shibatsuka  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  60-  (3)  475  -485  2008/06  [Not refereed][Not invited]
     
    The distribution and kinematics of molecular gas in the central region of the barred spiral galaxy Maffei 2 were investigated using a data set of (CO)-C-12 (1-0), (CO)-C-12 (2-1), CS (2-1) lines, and 103 GHz continuum. We found that the offset ridges along the kpc-scale bar continue to the central spiral structure embedded in a weak oval structure, which is regarded as an x2 orbit in the bar potential. The spiral structure continues toward the center, diverging from the oval structure. The size of these structures is less than R similar to 100 pc. The mass concentration within R = 35 pc is estimated to be 2 x 10(8) M-circle dot. The high mass concentration is consistent with theoretical predictions concerning the creation of such a nuclear spiral structure. A comparison with tracers of dense gas and star-forming region suggests that the dense molecular gas traced by the CS (2-1) line is formed at the crossing points of the x1 and x2 orbits and the star-forming region appears after 2 x 10(5) yr, which is comparable to the free-fall time of dense gas traced by the CS line (similar to 10(5) cm(-3)).
  • Akihiro Doi, Kenta Fujisawa, Makoto Inoue, Kiyoaki Wajima, Hiroshi Nagai, Keiichiro Harada, Kousuke Suematsu, Asao Habe, Mareki Honma, Noriyuki Kawaguchi, Eiji Kawai, Hideyuki Kobayashi, Yasuhiro Koyama, Hiromitsu Kuboki, Yasuhiro Murata, Toshihiro Omodaka, Kazuo Sorai, Hiroshi Sudou, Hiroshi Takaba, Kazuhiro Takashima, Koji Takeda, Sayaka Tamura, Ken-ichi Wakamatsu  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  59-  (4)  703  -709  2007/08  [Not refereed][Not invited]
     
    We performed phase-reference very long baseline interferometry (VLBI) observations on five radio-loud narrow-line Seyfert 1 galaxies (NLS1s) at 8.4 GHz with the Japanese VLBI Network. Each of the five targets (RXS J08066+7248, RXS J16290+4007, RXS J16333+4718, RXS J16446+2619, and 133 1702+457) in milli-Jansky levels were detected and unresolved in milli-arcsecond resolutions, i.e., with brightness temperatures higher than 107 K. The nonthermal processes of active galactic nucleus activity, rather than starbursts, are predominantly responsible for the radio emissions from these NLS1s. Out of the nine known radio-loud NLS1s, including those chosen for this study, we found that the four most radio-loud objects exclusively have inverted spectra. This suggests a possibility that these NLS1s are radio-loud due to Doppler beaming, which can apparently enhance both the radio power and the spectral frequency.
  • Akihiro Doi, Kenta Fujisawa, Makoto Inoue, Kiyoaki Wajima, Hiroshi Nagai, Keiichiro Harada, Kousuke Suematsu, Asao Habe, Mareki Honma, Noriyuki Kawaguchi, Eiji Kawai, Hideyuki Kobayashi, Yasuhiro Koyama, Hiromitsu Kuboki, Yasuhiro Murata, Toshihiro Omodaka, Kazuo Sorai, Hiroshi Sudou, Hiroshi Takaba, Kazuhiro Takashima, Koji Takeda, Sayaka Tamura, Ken-ichi Wakamatsu  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  59-  (4)  703  -709  2007/08  [Not refereed][Not invited]
     
    We performed phase-reference very long baseline interferometry (VLBI) observations on five radio-loud narrow-line Seyfert 1 galaxies (NLS1s) at 8.4 GHz with the Japanese VLBI Network. Each of the five targets (RXS J08066+7248, RXS J16290+4007, RXS J16333+4718, RXS J16446+2619, and 133 1702+457) in milli-Jansky levels were detected and unresolved in milli-arcsecond resolutions, i.e., with brightness temperatures higher than 107 K. The nonthermal processes of active galactic nucleus activity, rather than starbursts, are predominantly responsible for the radio emissions from these NLS1s. Out of the nine known radio-loud NLS1s, including those chosen for this study, we found that the four most radio-loud objects exclusively have inverted spectra. This suggests a possibility that these NLS1s are radio-loud due to Doppler beaming, which can apparently enhance both the radio power and the spectral frequency.
  • Kazuyuki Muraoka, Kotaro Kohno, Tomoka Tosaki, Nario Kuno, Kouichiro Nakanishi, Kazuo Sorai, Takeshi Okuda, Seiichi Sakamoto, Akira Endo, Bunyo Hatsukade, Kazuhisa Kamegai, Kunihiko Tanaka, Juan Cortes, Hajime Ezawa, Nobuyuki Yamaguchi, Takeshi Sakai, Ryohei Kawabe  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  59-  (1)  43  -54  2007/02  [Not refereed][Not invited]
     
    We present CO (J = 3-2) emission observations with the ASTE toward the 5' x 5' (or 6.6 kpc x 6.6 kpc at the distance D = 4.5 Mpc) region of the nearby barred spiral galaxy M 83. We successfully resolved the major structures, i.e., the nuclear starburst region, bar, and inner spiral arms at a resolution of 22" (480pc), showing a good spatial coincidence between CO and 6 cm continuum emissions. We found a global luminosity, L'(CO(3-2)), of 5.1 x 10(8) K km s(-1) pc(2) within the observed region. We also found L'(CO(3-2)) in a disk region (0.5 < r < 3.5 kpc) of 4.2 x 10(8) K km s(-1) pc(2), indicating that (J = 3-2) emission in the disk region significantly contributes to the global L'(CO(3-2)). From a comparison of CO (J = 3-2) data with CO (J = 1-0) intensities measured with the Nobeyama 45-m telescope, we found that the radial profile of the CO (J = 3-2)/CO (J = 1-0) integrated intensity ratio, R3-2/1-0, is almost unity in the central region (r < 0.25 kpc), whereas it drops to a constant value, 0.6-0.7, in the disk region. The radial profile of star formation efficiencies (SFEs), determined from 6 cm radio continuum and CO (J = 1-0) emission, shows the same trend as that of R3-2/1-0. At the bar-end (r similar to 2.4kpc), the amounts of molecular gas and the massive stars are enhanced when compared with other disk regions, whereas there is no excess of R3-2/1-0 and SFE in that region. This means that a simple summation of the star-forming regions at the bar-end and the disk cannot reproduce the nuclear starburst of M 83, implying that the spatial variation of the dense gas fraction traced by R3-2/1-0 governs the spatial variation of SFE in M 83.
  • Nario Kuno, Naoko Sato, Hiroyuki Nakanishi, Akihiko Hirota, Tomoka Tosaki, Yasuhiro Shioya, Kazuo Sorai, Naomasa Nakai, Kota Nishiyama, Baltsar Vila-Vilaro  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  59-  (1)  117  -166  2007/02  [Not refereed][Not invited]
     
    The data from a CO (J = 1-0) mapping survey of 40 nearby spiral galaxies, performed with the Nobeyama 45 m telescope, are presented. The criteria of the sample selection were: (1) RC3 morphological type ranging from Sa to Scd, (2) distance of less than 25 Mpc, (3) inclination angle less than 79 degrees (RC3), (4) flux at 100 mu m higher than 10 Jy, and (5) spiral structure not destroyed by any interaction. The maps of CO cover most of the optical disk of the galaxies. We investigated the influence of bars on the distribution of molecular gas in spiral galaxies using these data. We confirmed that the degree of the central concentration is higher in barred spirals than in nonbarred spirals, as shown by previous studies. Furthermore, we present observational evidence that bars are efficient in driving molecular gas that lies within the bar length toward the center, while the role in bringing gas in from the outer parts of the disks is small. The transported gas accounts for about half of the molecular gas within the central region in barred spiral galaxies. We found a correlation between the degree of central concentration and the bar strength. Galaxies with stronger bars tend to have a higher central concentration. The correlation implies that stronger bars accumulate molecular gas toward the center more efficiently. These results are consistent with long-lived bars.
  • Kazuyuki Muraoka, Kotaro Kohno, Tomoka Tosaki, Nario Kuno, Kouichiro Nakanishi, Kazuo Sorai, Takeshi Okuda, Seiichi Sakamoto, Akira Endo, Bunyo Hatsukade, Kazuhisa Kamegai, Kunihiko Tanaka, Juan Cortes, Hajime Ezawa, Nobuyuki Yamaguchi, Takeshi Sakai, Ryohei Kawabe  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  59-  (1)  43  -54  2007/02  [Not refereed][Not invited]
     
    We present CO (J = 3-2) emission observations with the ASTE toward the 5' x 5' (or 6.6 kpc x 6.6 kpc at the distance D = 4.5 Mpc) region of the nearby barred spiral galaxy M 83. We successfully resolved the major structures, i.e., the nuclear starburst region, bar, and inner spiral arms at a resolution of 22" (480pc), showing a good spatial coincidence between CO and 6 cm continuum emissions. We found a global luminosity, L'(CO(3-2)), of 5.1 x 10(8) K km s(-1) pc(2) within the observed region. We also found L'(CO(3-2)) in a disk region (0.5 < r < 3.5 kpc) of 4.2 x 10(8) K km s(-1) pc(2), indicating that (J = 3-2) emission in the disk region significantly contributes to the global L'(CO(3-2)). From a comparison of CO (J = 3-2) data with CO (J = 1-0) intensities measured with the Nobeyama 45-m telescope, we found that the radial profile of the CO (J = 3-2)/CO (J = 1-0) integrated intensity ratio, R3-2/1-0, is almost unity in the central region (r < 0.25 kpc), whereas it drops to a constant value, 0.6-0.7, in the disk region. The radial profile of star formation efficiencies (SFEs), determined from 6 cm radio continuum and CO (J = 1-0) emission, shows the same trend as that of R3-2/1-0. At the bar-end (r similar to 2.4kpc), the amounts of molecular gas and the massive stars are enhanced when compared with other disk regions, whereas there is no excess of R3-2/1-0 and SFE in that region. This means that a simple summation of the star-forming regions at the bar-end and the disk cannot reproduce the nuclear starburst of M 83, implying that the spatial variation of the dense gas fraction traced by R3-2/1-0 governs the spatial variation of SFE in M 83.
  • Nario Kuno, Naoko Sato, Hiroyuki Nakanishi, Akihiko Hirota, Tomoka Tosaki, Yasuhiro Shioya, Kazuo Sorai, Naomasa Nakai, Kota Nishiyama, Baltsar Vila-Vilaro  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  59-  (1)  117  -166  2007/02  [Not refereed][Not invited]
     
    The data from a CO (J = 1-0) mapping survey of 40 nearby spiral galaxies, performed with the Nobeyama 45 m telescope, are presented. The criteria of the sample selection were: (1) RC3 morphological type ranging from Sa to Scd, (2) distance of less than 25 Mpc, (3) inclination angle less than 79 degrees (RC3), (4) flux at 100 mu m higher than 10 Jy, and (5) spiral structure not destroyed by any interaction. The maps of CO cover most of the optical disk of the galaxies. We investigated the influence of bars on the distribution of molecular gas in spiral galaxies using these data. We confirmed that the degree of the central concentration is higher in barred spirals than in nonbarred spirals, as shown by previous studies. Furthermore, we present observational evidence that bars are efficient in driving molecular gas that lies within the bar length toward the center, while the role in bringing gas in from the outer parts of the disks is small. The transported gas accounts for about half of the molecular gas within the central region in barred spiral galaxies. We found a correlation between the degree of central concentration and the bar strength. Galaxies with stronger bars tend to have a higher central concentration. The correlation implies that stronger bars accumulate molecular gas toward the center more efficiently. These results are consistent with long-lived bars.
  • Hiroyuki Nakanishi, Nario Kuno, Yoshiaki Sofue, Naoko Sato, Naomasa Nakai, Yasuhiro Shioya, Tomoka Tosaki, Sachiko Onodera, Kazuo Sorai, Fumi Egusa, Akihiko Hirota  ASTROPHYSICAL JOURNAL  651-  (2)  804  -810  2006/11  [Not refereed][Not invited]
     
    We found high molecular fractions (f(mol); ratio of the molecular to total gas surface densities) in three of five Virgo spiral galaxies in spite of their low total gas column density, based on (CO)-C-12 J = 1-0 observations with the Nobeyama 45 m telescope equipped with a multibeam receiver, BEARS. We interpret this as a result of environmental effects. Combining the CO data with H I data, the relationship between the surface density of the total gas (H I plus H-2) and fmol indicates that the three galaxies near the cluster center have larger fmol values than expected for field galaxies, while the others show normal fmol. The large fmol is interpreted as being due either to effective H I gas stripping, even in the inner disks, or to large ISM pressure induced by the high ICM pressure and/or ram pressure, although the possibility of an unusually high metallicity cannot be ruled out.
  • Hiroyuki Nakanishi, Nario Kuno, Yoshiaki Sofue, Naoko Sato, Naomasa Nakai, Yasuhiro Shioya, Tomoka Tosaki, Sachiko Onodera, Kazuo Sorai, Fumi Egusa, Akihiko Hirota  ASTROPHYSICAL JOURNAL  651-  (2)  804  -810  2006/11  [Not refereed][Not invited]
     
    We found high molecular fractions (f(mol); ratio of the molecular to total gas surface densities) in three of five Virgo spiral galaxies in spite of their low total gas column density, based on (CO)-C-12 J = 1-0 observations with the Nobeyama 45 m telescope equipped with a multibeam receiver, BEARS. We interpret this as a result of environmental effects. Combining the CO data with H I data, the relationship between the surface density of the total gas (H I plus H-2) and fmol indicates that the three galaxies near the cluster center have larger fmol values than expected for field galaxies, while the others show normal fmol. The large fmol is interpreted as being due either to effective H I gas stripping, even in the inner disks, or to large ISM pressure induced by the high ICM pressure and/or ram pressure, although the possibility of an unusually high metallicity cannot be ruled out.
  • Hiroshi Imai, Toshihiro Omodaka, Tomoya Hirota, Tomofumi Umemoto, Kazuo Sorai, Tetsuro Kondo  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  58-  (5)  883  -892  2006/10  [Not refereed][Not invited]
     
    We report on H2O masers associated with the massive-star forming region G192.16-3.84 observed with the new Japanese VLBI network at three epochs spanned for two months, which have revealed the three-dimensional kinematical structure of the whole H2O maser region in G192.16-3.84, containing two young stellar objects separated by similar to 1200AU. The maser spatio-kinematical structure has well persisted since previous observations, in which the masers are expected to be associated with a highly collimated bipolar jet and an infalling-rotating disk in the northern and southern clusters of H2O maser features, respectively. We estimated a jet expansion speed of similar to 100 km s(-1) and re-estimated the dynamical age of the whole jet to be 5.6 x 10(4) yr. We investigated the spatial distribution of the Doppler velocities during the previous and present observations and the relative proper motions of H2O maser features in the southern cluster, as well as the relative bulk motion between the two maser clusters. They are well explained by a model of an infalling-rotating disk with a radius of similar to 1000 AU and a central stellar mass of 5-10 M-circle dot, rather than by a model of a bipolar jet perpendicular to the observed CO outflow. Based on the derived H2O maser spatio-kinematical parameters, we discuss the formation mechanism of the massive young stellar objects and the outflow development in G192.16-3.84.
  • Hiroshi Imai, Toshihiro Omodaka, Tomoya Hirota, Tomofumi Umemoto, Kazuo Sorai, Tetsuro Kondo  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  58-  (5)  883  -892  2006/10  [Not refereed][Not invited]
     
    We report on H2O masers associated with the massive-star forming region G192.16-3.84 observed with the new Japanese VLBI network at three epochs spanned for two months, which have revealed the three-dimensional kinematical structure of the whole H2O maser region in G192.16-3.84, containing two young stellar objects separated by similar to 1200AU. The maser spatio-kinematical structure has well persisted since previous observations, in which the masers are expected to be associated with a highly collimated bipolar jet and an infalling-rotating disk in the northern and southern clusters of H2O maser features, respectively. We estimated a jet expansion speed of similar to 100 km s(-1) and re-estimated the dynamical age of the whole jet to be 5.6 x 10(4) yr. We investigated the spatial distribution of the Doppler velocities during the previous and present observations and the relative proper motions of H2O maser features in the southern cluster, as well as the relative bulk motion between the two maser clusters. They are well explained by a model of an infalling-rotating disk with a radius of similar to 1000 AU and a central stellar mass of 5-10 M-circle dot, rather than by a model of a bipolar jet perpendicular to the observed CO outflow. Based on the derived H2O maser spatio-kinematical parameters, we discuss the formation mechanism of the massive young stellar objects and the outflow development in G192.16-3.84.
  • N Sato, A Yamauchi, Y Ishihara, K Sorai, N Kuno, N Nakai, R Balasubramanyam, P Hall  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  57-  (4)  587  -594  2005/08  [Not refereed][Not invited]
     
    We made a survey of water-vapor maser emission for 93 AGNs with the Nobeyama 45-m and Mopra 22-m telescopes from 1999 to 2002. A megamaser was detected in a Seyfert 2 galaxy, NGC 6926, at a distance of 80 Mpc, in 2002 June. [Greenhill et al. (2003a) have also reported a detection of the megamaser at the close date.] The peak flux density was 110 mJy, and the total isotropic luminosity was 340 L-circle dot. The maser shows triply peaked spectrum, suggesting an edge-on disk. A narrow-line feature of the maser components at Y-LSR = 6001 km s(-1) was strongly variable with a time scale of a few tens of days, and the variation should be of intrinsic origin. We also showed a possibility of variability of water-vapor maser emission of a megamaser previously detected in a Seyfert/ultraluminous FIR galaxy, NGC 6240.
  • N Sato, A Yamauchi, Y Ishihara, K Sorai, N Kuno, N Nakai, R Balasubramanyam, P Hall  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  57-  (4)  587  -594  2005/08  [Not refereed][Not invited]
     
    We made a survey of water-vapor maser emission for 93 AGNs with the Nobeyama 45-m and Mopra 22-m telescopes from 1999 to 2002. A megamaser was detected in a Seyfert 2 galaxy, NGC 6926, at a distance of 80 Mpc, in 2002 June. [Greenhill et al. (2003a) have also reported a detection of the megamaser at the close date.] The peak flux density was 110 mJy, and the total isotropic luminosity was 340 L-circle dot. The maser shows triply peaked spectrum, suggesting an edge-on disk. A narrow-line feature of the maser components at Y-LSR = 6001 km s(-1) was strongly variable with a time scale of a few tens of days, and the variation should be of intrinsic origin. We also showed a possibility of variability of water-vapor maser emission of a megamaser previously detected in a Seyfert/ultraluminous FIR galaxy, NGC 6240.
  • Environmental effects on gaseous disks of Virgo spiral galaxies
    Nakanishi, Hiroyuki, Kuno, Nario, Sofue, Yoshiaki, Sato, Naoko, Nakai, Naomasa, Shioya, Yasuhiro, Tosaki, Tomoka, Onodera, Sachiko, Sorai, Kazuo, Egusa, Fumi, Hirota, Akihiko  In: Proceedings of the dusty and molecular universe: a prelude to Herschel and ALMA, editted by A. Wilson, p.301 - 302  207  -208  2005  [Not refereed][Not invited]
  • Nobeyama CO Atlas of Nearby Spiral Galaxies
    Nario Kuno, Naomasa Nakai, Kazuo Sorai, Naoko Sato, Aya Ymauchi, Tomoka Tosaki, Yoshiyuki Shioya, Baltasar Vila-Vilaró, Kohta Nishiyama, Yuko Ishihara, J. Cepa  ASP Conference Proceedings 249, The Central Kiloparsec of Starbursts and AGN: The La Palma Connection, editted by J. H. Knapen, J. E. Beckman, I. Shlosman, T. J. Mahoney  71  -72  2003  [Not refereed][Not invited]
  • Physical Conditions and Structure of Molecular Gas in the Galactic Center
    Tsuyoshi Sawada, Tetsuo Hasegawa, Toshihiro Handa, Jun-Ichi Morino, Kumiko S. Usuda, Kazuo Sorai, Tomoharu Oka, Masumichi Seta, Seiichi Sakamoto, Masahiko Hayashi, Roy Booth, Leonard Bronfman, Abraham L. Castellanos, Lars-Åke Nyman, Peter Shaver, R. J. Cohen  ASP Conference Proceedings 289, The Proceedings of the IAU 8th Asian-Pacific Regional Meeting, editted by S. Ikeuchi, J. Hearnshaw, and T. Hanawa, the Astronomical Society of Japan  207  -208  2003  [Not refereed][Not invited]
  • Nobeyama CO Atlas of Nearby Spiral Galaxies
    Nario Kuno, Naomasa Nakai, Kazuo Sorai, Naoko Sato, Aya Ymauchi, Tomoka Tosaki, Yoshiyuki Shioya, Baltasar Vila-Vilaró, Kohta Nishiyama, Yuko Ishihara, J. Cepa  ASP Conference Proceedings 249, The Central Kiloparsec of Starbursts and AGN: The La Palma Connection, editted by J. H. Knapen, J. E. Beckman, I. Shlosman, T. J. Mahoney  71  -72  2003  [Not refereed][Not invited]
  • Physical Conditions and Structure of Molecular Gas in the Galactic Center
    Tsuyoshi Sawada, Tetsuo Hasegawa, Toshihiro Handa, Jun-Ichi Morino, Kumiko S. Usuda, Kazuo Sorai, Tomoharu Oka, Masumichi Seta, Seiichi Sakamoto, Masahiko Hayashi, Roy Booth, Leonard Bronfman, Abraham L. Castellanos, Lars-Åke Nyman, Peter Shaver, R. J. Cohen  ASP Conference Proceedings 289, The Proceedings of the IAU 8th Asian-Pacific Regional Meeting, editted by S. Ikeuchi, J. Hearnshaw, and T. Hanawa, the Astronomical Society of Japan  207  -208  2003  [Not refereed][Not invited]
  • N Kuno, N Nakai, K Sorai, K Nishiyama, B Vila-Vilaro  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  54-  (4)  555  -560  2002/08  [Not refereed][Not invited]
     
    We made CO and HCN simultaneous observations of lenticular galaxies (NGC 404, NGC 3593, and NGC 4293) and detected HCN emission in NGC 3593 and NGC 4293 as well as CO in all the galaxies. The I-HCN/I-CO ratios were 0.025+/-0.006 and 0.066+/-0.005 in NGC 3593 and NGC 4293, respectively, which are comparable to that of late-type spiral galaxies. The average of the I-HCN/I-CO ratios at the center of 12 nearby spiral galaxies including the late type was 0.055+/-0.028. The line profiles of CO and HCN emission showed different shape in both galaxies. The HCN peaks were not at the systemic velocity of these galaxies, while the CO peaks were near the systemic velocity. These results suggest that the fraction of dense molecular gas is high around the center of these galaxies.
  • N Kuno, N Nakai, K Sorai, K Nishiyama, B Vila-Vilaro  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  54-  (4)  555  -560  2002/08  [Not refereed][Not invited]
     
    We made CO and HCN simultaneous observations of lenticular galaxies (NGC 404, NGC 3593, and NGC 4293) and detected HCN emission in NGC 3593 and NGC 4293 as well as CO in all the galaxies. The I-HCN/I-CO ratios were 0.025+/-0.006 and 0.066+/-0.005 in NGC 3593 and NGC 4293, respectively, which are comparable to that of late-type spiral galaxies. The average of the I-HCN/I-CO ratios at the center of 12 nearby spiral galaxies including the late type was 0.055+/-0.028. The line profiles of CO and HCN emission showed different shape in both galaxies. The HCN peaks were not at the systemic velocity of these galaxies, while the CO peaks were near the systemic velocity. These results suggest that the fraction of dense molecular gas is high around the center of these galaxies.
  • K Sorai, N Nakai, N Kuno, K Nishiyama  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  54-  (2)  179  -194  2002/04  [Not refereed][Not invited]
     
    Simultaneous observations of HCN and CO lines were made along the major axes of six nearby CO bright galaxies with the Nobeyama 45-m telescope. The beam-averaged HCN/CO ratios are 0.01 to 0.1. The distributions of the HCN/CO ratio along the major axes (and the minor axis for M 5 1) show different patterns from one galaxy to another. By adding data obtained from the outer disk, however, we found gradual decreases in the HCN and CO intensities and the HCN/CO ratio with increasing radius in M 51 from the nuclear region to 3 kpc, similar to our previous result for NGC 253. The HCN/CO ratio is very sensitive to the observing beam size on a linear scale. The ratio, which reflects the fraction of dense molecular gas, correlates with the star-formation activity derived from the far-infrared luminosity.
  • K Sorai, N Nakai, N Kuno, K Nishiyama  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  54-  (2)  179  -194  2002/04  [Not refereed][Not invited]
     
    Simultaneous observations of HCN and CO lines were made along the major axes of six nearby CO bright galaxies with the Nobeyama 45-m telescope. The beam-averaged HCN/CO ratios are 0.01 to 0.1. The distributions of the HCN/CO ratio along the major axes (and the minor axis for M 5 1) show different patterns from one galaxy to another. By adding data obtained from the outer disk, however, we found gradual decreases in the HCN and CO intensities and the HCN/CO ratio with increasing radius in M 51 from the nuclear region to 3 kpc, similar to our previous result for NGC 253. The HCN/CO ratio is very sensitive to the observing beam size on a linear scale. The ratio, which reflects the fraction of dense molecular gas, correlates with the star-formation activity derived from the far-infrared luminosity.
  • S Okumura, R Miyawaki, K Sorai, T Yamashita, T Hasegawa  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  53-  (5)  793  -798  2001/10  [Not refereed][Not invited]
     
    We present a high-resolution (16") (CO)-C-13 (J = 1-0) map of the central region of W 51. We observed an area of about 15.'3 x 16.'7, which covers the entire region of G49.5-0.4, the brightest source in the W 51 region. Four discrete molecular clouds were identified toward G49.5-0.4, and evidence of cloud-cloud collisions was found. We speculate that a "pileup" of three molecular clouds resulted in a burst of massive star formation in G49.5-0.4.
  • S Okumura, R Miyawaki, K Sorai, T Yamashita, T Hasegawa  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  53-  (5)  793  -798  2001/10  [Not refereed][Not invited]
     
    We present a high-resolution (16") (CO)-C-13 (J = 1-0) map of the central region of W 51. We observed an area of about 15.'3 x 16.'7, which covers the entire region of G49.5-0.4, the brightest source in the W 51 region. Four discrete molecular clouds were identified toward G49.5-0.4, and evidence of cloud-cloud collisions was found. We speculate that a "pileup" of three molecular clouds resulted in a burst of massive star formation in G49.5-0.4.
  • T Sawada, T Hasegawa, T Handa, JI Morino, T Oka, R Booth, L Bronfman, M Hayashi, AL Castellanos, LA Nyman, S Sakamoto, M Seta, P Shaver, K Sorai, KS Usuda  ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES  136-  (1)  189  -219  2001/09  [Not refereed][Not invited]
     
    As a part of the Tokyo-Onsala-ESO-Calan Galactic CO survey, we have made large-scale mapping observations of the Galactic center in the CO J = 2-1 line using the 60 cm survey telescope in Chile. The data were taken with the same beam size (9 ') and sampling grid (7.'5) as the CO J = 1-0 Columbia survey, so that the two data sets can be compared directly. Velocity channel maps and longitude-velocity diagrams of the (CO)-C-12 J = 2-1 line, covering - 6 degrees less than or equal to I less than or equal to 6 degrees, - 2 degrees less than or equal to b less than or equal to 2 degrees, -300 less than or equal to nu (LSR) less than or equal to 300 km s(-1), are presented, along with the corresponding maps of the (CO)-C-12 J = 2-1/1J = 1-0 intensity ratio [R2-1/1-0((CO)-C-12)]. A longitude-velocity diagram of the (CO)-C-13 J = 2-1 line intensity and corresponding (CO)-C-13 J = 2-1/(CO)-C-12 J = 2-1 intensity ratio [R-13/12(J = 2-1)] is also presented at b = 0 degrees. The overall R2-1/1-0((CO)-C-12) in the central 900 pc of the Galaxy is 0.96 +/- 0.01, which is higher than the typical value in the Galactic disk, 0.6-0.7. The isotopic intensity ratio R-13/12(J = 2-1) is 0.10 +/- 0.01. The two observed intensity ratios [R2-1/1-0((CO)-C-12) and R-13/12(j = 2-1)] indicate that the optical depth of the (CO)-C-12 J = 1-0 line is similar to1 or smaller in the Galactic center molecular clouds, much smaller than those of the giant molecular clouds (GMCs) in the Galactic disk. Longitude-velocity distributions of physical properties of molecular gas are derived using a large velocity gradient analysis. Molecular gas in the Galactic center generally shows a high pressure. In particular, there is a high-pressure region in the central similar to 100 pc where the pressure is an order of magnitude higher than that in GMCs in the Galactic disk. This region is dominated by high-density gas and contains star-forming regions.
  • T Sawada, T Hasegawa, T Handa, JI Morino, T Oka, R Booth, L Bronfman, M Hayashi, AL Castellanos, LA Nyman, S Sakamoto, M Seta, P Shaver, K Sorai, KS Usuda  ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES  136-  (1)  189  -219  2001/09  [Not refereed][Not invited]
     
    As a part of the Tokyo-Onsala-ESO-Calan Galactic CO survey, we have made large-scale mapping observations of the Galactic center in the CO J = 2-1 line using the 60 cm survey telescope in Chile. The data were taken with the same beam size (9 ') and sampling grid (7.'5) as the CO J = 1-0 Columbia survey, so that the two data sets can be compared directly. Velocity channel maps and longitude-velocity diagrams of the (CO)-C-12 J = 2-1 line, covering - 6 degrees less than or equal to I less than or equal to 6 degrees, - 2 degrees less than or equal to b less than or equal to 2 degrees, -300 less than or equal to nu (LSR) less than or equal to 300 km s(-1), are presented, along with the corresponding maps of the (CO)-C-12 J = 2-1/1J = 1-0 intensity ratio [R2-1/1-0((CO)-C-12)]. A longitude-velocity diagram of the (CO)-C-13 J = 2-1 line intensity and corresponding (CO)-C-13 J = 2-1/(CO)-C-12 J = 2-1 intensity ratio [R-13/12(J = 2-1)] is also presented at b = 0 degrees. The overall R2-1/1-0((CO)-C-12) in the central 900 pc of the Galaxy is 0.96 +/- 0.01, which is higher than the typical value in the Galactic disk, 0.6-0.7. The isotopic intensity ratio R-13/12(J = 2-1) is 0.10 +/- 0.01. The two observed intensity ratios [R2-1/1-0((CO)-C-12) and R-13/12(j = 2-1)] indicate that the optical depth of the (CO)-C-12 J = 1-0 line is similar to1 or smaller in the Galactic center molecular clouds, much smaller than those of the giant molecular clouds (GMCs) in the Galactic disk. Longitude-velocity distributions of physical properties of molecular gas are derived using a large velocity gradient analysis. Molecular gas in the Galactic center generally shows a high pressure. In particular, there is a high-pressure region in the central similar to 100 pc where the pressure is an order of magnitude higher than that in GMCs in the Galactic disk. This region is dominated by high-density gas and contains star-forming regions.
  • K Sorai, T Hasegawa, RS Booth, M Rubio, JI Morino, L Bronfman, T Handa, M Hayashi, LA Nyman, T Oka, S Sakamoto, M Seta, KS Usuda  ASTROPHYSICAL JOURNAL  551-  (2)  794  -802  2001/04  [Not refereed][Not invited]
     
    We observed 34 positions throughout the disk of the Large Magellanic Cloud in the CO J = 2-1 emission line with the 60 cm radio telescope. Comparing the spectra with Tokyo-Onsala-ESO-Calan those of the J = 1-0 line at the same angular resolution (similar or equal to 9', or 130 pc at 50 kpc), we found that the CO J = 2-1/J = 1-0 intensity ratio (R2-1/1-0) scatters in a range of 0.5-1.3. The luminosity ratio aver aged for all observed points is 0.92 +/- 0.05. The ratio R2-1/1-0 is approximately unity (0.95 +/- 0.06) in 30 Dor, consistent with optically thick and thermalized emission, even in the southern part where massive star formation does not occur yet. This suggests that the high R2-1/1-0 is not primarily due to the UV radiation from young stars but rather to the intrinsic nature of the molecular gas that is relatively dense (greater than or similar to 10(3) cm(-3)) and may be ready to form stars. In addition to a cloud-to-cloud difference of R2-1/1-0, there exists a radial gradient of the ratio of 0.94 +/- 0.11 in the inner region (less than or similar to2 kpc from the kinematic center) and 0.69 +/- 0.11 in the outer region (greater than or similar to2 kpc from the center, excluding the 30 Doradus complex). The higher R2-1/1-0 in the inner galaxy might be due to relatively higher gas densities within CO clumps in molecular clouds and/or higher external heating in that region.
  • K Sorai, T Hasegawa, RS Booth, M Rubio, JI Morino, L Bronfman, T Handa, M Hayashi, LA Nyman, T Oka, S Sakamoto, M Seta, KS Usuda  ASTROPHYSICAL JOURNAL  551-  (2)  794  -802  2001/04  [Not refereed][Not invited]
     
    We observed 34 positions throughout the disk of the Large Magellanic Cloud in the CO J = 2-1 emission line with the 60 cm radio telescope. Comparing the spectra with Tokyo-Onsala-ESO-Calan those of the J = 1-0 line at the same angular resolution (similar or equal to 9', or 130 pc at 50 kpc), we found that the CO J = 2-1/J = 1-0 intensity ratio (R2-1/1-0) scatters in a range of 0.5-1.3. The luminosity ratio aver aged for all observed points is 0.92 +/- 0.05. The ratio R2-1/1-0 is approximately unity (0.95 +/- 0.06) in 30 Dor, consistent with optically thick and thermalized emission, even in the southern part where massive star formation does not occur yet. This suggests that the high R2-1/1-0 is not primarily due to the UV radiation from young stars but rather to the intrinsic nature of the molecular gas that is relatively dense (greater than or similar to 10(3) cm(-3)) and may be ready to form stars. In addition to a cloud-to-cloud difference of R2-1/1-0, there exists a radial gradient of the ratio of 0.94 +/- 0.11 in the inner region (less than or similar to2 kpc from the kinematic center) and 0.69 +/- 0.11 in the outer region (greater than or similar to2 kpc from the center, excluding the 30 Doradus complex). The higher R2-1/1-0 in the inner galaxy might be due to relatively higher gas densities within CO clumps in molecular clouds and/or higher external heating in that region.
  • GALAXY-Real-time VLBI for Radio Astronomy Observations
    Kenta Fujikawa, Noriyuki Kawaguchi, Hideyuki Kobayashi, Satoru Iguchi, Takeshi Miyajim, Kazuo Sorai, Tetsuro Kondo, Yasuhiro Koyama, Junichi Nakajima, Mamoru Sekido, Hiro Osaki, Hiroshi Okudo, Hitoshi Kiuchi, Yukio Takahashi, Akihiro Kaneko, Hisashi Hirabayashi, Yasuhiro Murata, Hisao Uose, Sotetsu Iwamura, Takashi Hoshino  Journal of the Communication Research Laboratory  (46)  47  -58  2001  [Not refereed][Not invited]
  • N Kuno, K Nishiyama, N Nakai, K Sorai, B Vila-Vilaro, T Handa  GALAXY DISKS AND DISK GALAXIES  230-  379  -380  2001  [Not refereed][Not invited]
     
    We present the results of the CO mapping observations of the barred spiral galaxy NGC 3504 with the Nobeyama 45-m telescope. The distribution of the molecular gas shows offset ridges which correspond to the distribution of H II regions along the bar. The velocity perpendicular to the bar decreases abruptly at the ridge. We propose new method to derive the pattern speed of the bar.
  • K Sorai, N Nakai, K Nishiyama  GALAXY DISKS AND DISK GALAXIES  230-  385  -386  2001  [Not refereed][Not invited]
     
    We observed HCN (J=1-0) and (CO)-C-13 (J=1-0) simultaneously toward the nuclear region and the disk of the nearby barred spiral galaxy NGC 253 and compared with (CO)-C-12 (J=1-0) data. The HCN/(CO)-C-13 and HCN/(CO)-C-12 ratios are higher in the nuclear region than those in the disk, which indicates that the molecular gas in the nuclear region is dense and hot, while less dense in the disk, based on the one-zone large velocity gradient model. We also observed HCN and (CO)-C-12 simultaneously along the major axes of nearby CO bright galaxies.
  • Dense Molecular Gas in Early-Type Galaxies
    Nario Kuno, Naomasa Nakai, Baltasar Vila-Vilaró, Kohta Nishiyama, Kazuo Sorai  ASP Conference Proceedings 249, The Central Kiloparsec of Starbursts and AGN: The La Palma Connection, editted by J. H. Knapen, J. E. Beckman, I. Shlosman, T. J. Mohoney  695  2001  [Not refereed][Not invited]
  • GALAXY-Real-time VLBI for Radio Astronomy Observations
    Kenta Fujikawa, Noriyuki Kawaguchi, Hideyuki Kobayashi, Satoru Iguchi, Takeshi Miyajim, Kazuo Sorai, Tetsuro Kondo, Yasuhiro Koyama, Junichi Nakajima, Mamoru Sekido, Hiro Osaki, Hiroshi Okudo, Hitoshi Kiuchi, Yukio Takahashi, Akihiro Kaneko, Hisashi Hirabayashi, Yasuhiro Murata, Hisao Uose, Sotetsu Iwamura, Takashi Hoshino  Journal of the Communication Research Laboratory  (46)  47  -58  2001  [Not refereed][Not invited]
  • N Kuno, K Nishiyama, N Nakai, K Sorai, B Vila-Vilaro, T Handa  GALAXY DISKS AND DISK GALAXIES  230-  379  -380  2001  [Not refereed][Not invited]
     
    We present the results of the CO mapping observations of the barred spiral galaxy NGC 3504 with the Nobeyama 45-m telescope. The distribution of the molecular gas shows offset ridges which correspond to the distribution of H II regions along the bar. The velocity perpendicular to the bar decreases abruptly at the ridge. We propose new method to derive the pattern speed of the bar.
  • HCN/CO Ratio in the Nuclear Regions and the Disks of Nearby Spiral Galaxies
    Kazuo Sorai, Naomasa Nakai, Nario Kuno, Kohta Nishiyama  ASP Conference Series 230, Galaxy Disks and Disk Galaxies, editted by J. G. Funes, S. J. and E. M. Corsini  385  -386  2001  [Not refereed][Not invited]
  • Dense Molecular Gas in Early-Type Galaxies
    Nario Kuno, Naomasa Nakai, Baltasar Vila-Vilaró, Kohta Nishiyama, Kazuo Sorai  ASP Conference Proceedings 249, The Central Kiloparsec of Starbursts and AGN: The La Palma Connection, editted by J. H. Knapen, J. E. Beckman, I. Shlosman, T. J. Mohoney  695  2001  [Not refereed][Not invited]
  • N Kuno, K Nishiyama, N Nakai, K Sorai, B Vila-Vilaro, T Handa  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  52-  (5)  775  -783  2000/10  [Not refereed][Not invited]
     
    We present the results of CO mapping observations of the barred spiral galaxy NGC 3504 with the Nobeyama 45-m telescope. The distribution of the molecular gas shows offset ridges which correspond to the distribution of H II regions along the bar. The velocity perpendicular to the bar decreases abruptly at the ridge. The velocity change implies that the molecular gas changes the direction of its motion to parallel to the bar at the ridge. Since the position angle of the major axis of the bar and the line of nodes are almost the same in NGC 3504, an upper limit to the pattern speed of the bar can be derived directly from the radial velocity. The resultant upper limit is 41 km s(-1) kpc(-1), which is much smaller than that derived based on an assumption that the corotation radius is located at the end of the bar (77 km s(-1) kpc(-1)). The corotation radius derived from our upper limit is more than two-times larger than the length of the semi-major axis of the bar in NGC 3504.
  • K Sorai, N Nakai, N Kuno, K Nishiyama, T Hasegawa  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  52-  (5)  785  -802  2000/10  [Not refereed][Not invited]
     
    The large scale mapping of the disk of a nearby barred galaxy, NGC 253 in CO (J = 1-0), was made with an angular resolution of 16". Molecular gas concentrates in the nuclear region and the large-scale bar seen in near-infrared images. The radial distribution of molecular gas indicates a secondary peak, whose radius agrees with that of the H alpha ring and the ends of the bar, as well as a central strong peak. The radial distribution is well fitted by an exponential function or a power law outside the secondary peak. A rotation curve is rising in the inner region and changes to flat at the ring. These facts suggest that molecular gas infalls from the outer disk by losing angular momentum due to gaseous viscosity in the region of the differential rotation, and accumulates at the ring. In the bar region land within the corotation radius), molecular gas again loses its angular momentum due to the bar potential, and is infalling toward the nuclear region. The upper limit of the noncircular motion along the major axis of the bar in the leading edge of the bar is approximate to 70-130 km s(-1) in the rest frame of the bar.
  • N Kuno, K Nishiyama, N Nakai, K Sorai, B Vila-Vilaro, T Handa  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  52-  (5)  775  -783  2000/10  [Not refereed][Not invited]
     
    We present the results of CO mapping observations of the barred spiral galaxy NGC 3504 with the Nobeyama 45-m telescope. The distribution of the molecular gas shows offset ridges which correspond to the distribution of H II regions along the bar. The velocity perpendicular to the bar decreases abruptly at the ridge. The velocity change implies that the molecular gas changes the direction of its motion to parallel to the bar at the ridge. Since the position angle of the major axis of the bar and the line of nodes are almost the same in NGC 3504, an upper limit to the pattern speed of the bar can be derived directly from the radial velocity. The resultant upper limit is 41 km s(-1) kpc(-1), which is much smaller than that derived based on an assumption that the corotation radius is located at the end of the bar (77 km s(-1) kpc(-1)). The corotation radius derived from our upper limit is more than two-times larger than the length of the semi-major axis of the bar in NGC 3504.
  • K Sorai, N Nakai, N Kuno, K Nishiyama, T Hasegawa  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN  52-  (5)  785  -802  2000/10  [Not refereed][Not invited]
     
    The large scale mapping of the disk of a nearby barred galaxy, NGC 253 in CO (J = 1-0), was made with an angular resolution of 16". Molecular gas concentrates in the nuclear region and the large-scale bar seen in near-infrared images. The radial distribution of molecular gas indicates a secondary peak, whose radius agrees with that of the H alpha ring and the ends of the bar, as well as a central strong peak. The radial distribution is well fitted by an exponential function or a power law outside the secondary peak. A rotation curve is rising in the inner region and changes to flat at the ring. These facts suggest that molecular gas infalls from the outer disk by losing angular momentum due to gaseous viscosity in the region of the differential rotation, and accumulates at the ring. In the bar region land within the corotation radius), molecular gas again loses its angular momentum due to the bar potential, and is infalling toward the nuclear region. The upper limit of the noncircular motion along the major axis of the bar in the leading edge of the bar is approximate to 70-130 km s(-1) in the rest frame of the bar.
  • H Kiuchi, Y Takahashi, A Kaneko, H Uose, S Iwamura, T Hoshino, N Kawaguchi, H Kobayashi, K Fujisawa, J Amagai, J Nakajima, T Kondo, S Iguchi, T Miyaji, K Sorai, K Sebata, T Yoshino, N Kurihara  IEICE TRANSACTIONS ON COMMUNICATIONS  E83B-  (2)  238  -245  2000/02  [Not refereed][Not invited]
     
    The Communications Research Laboratory (CRL), the National Astronomical Observatory (NAO), the Institute of Space and Astronoutical Science (ISAS), and the Telecommunication Network Laboratory Group of Nippon Telegraph and Telephone Corporation (NTT) have developed a very-long-baseline-connected-interferometry array, maximum baseline-length was 208 km, using a highspeed asynchronous transfer mode (ATM) network with an AAL1 that corresponds to the constant bit-rate protocol. The very long baseline interferometry (VLBI) observed data is transmitted through a 2.488-Gbps [STM-16/OC-48] ATM network instead of being recorded onto magnetic tape. By combining antennas via a high-speed ATM network, a highly-sensitive virtual (radio) telescope system was realized. The system was composed of two real-time VLBI networks: the Kry-Stone-Project (KSP) network of CRL (which is used for measuring crustal deformation in the Tokyo metropolitan area), and the OLIVE (optically linked VLBI experiment) network of NAO and ISAS which is used for astronomy (space-VLBI). These networks operated in cooperation with NTT. In order to realize a virtual telescope, the acquired VLBI data were corrected via the ATM networks and were synthesized using the VLBI technique. The cross-correlation processing and data observation were done simultaneously in this system and radio flares on the weak radio source (HR1099) were detected.
  • H Kiuchi, Y Takahashi, A Kaneko, H Uose, S Iwamura, T Hoshino, N Kawaguchi, H Kobayashi, K Fujisawa, J Amagai, J Nakajima, T Kondo, S Iguchi, T Miyaji, K Sorai, K Sebata, T Yoshino, N Kurihara  IEICE TRANSACTIONS ON COMMUNICATIONS  E83B-  (2)  238  -245  2000/02  [Not refereed][Not invited]
     
    The Communications Research Laboratory (CRL), the National Astronomical Observatory (NAO), the Institute of Space and Astronoutical Science (ISAS), and the Telecommunication Network Laboratory Group of Nippon Telegraph and Telephone Corporation (NTT) have developed a very-long-baseline-connected-interferometry array, maximum baseline-length was 208 km, using a highspeed asynchronous transfer mode (ATM) network with an AAL1 that corresponds to the constant bit-rate protocol. The very long baseline interferometry (VLBI) observed data is transmitted through a 2.488-Gbps [STM-16/OC-48] ATM network instead of being recorded onto magnetic tape. By combining antennas via a high-speed ATM network, a highly-sensitive virtual (radio) telescope system was realized. The system was composed of two real-time VLBI networks: the Kry-Stone-Project (KSP) network of CRL (which is used for measuring crustal deformation in the Tokyo metropolitan area), and the OLIVE (optically linked VLBI experiment) network of NAO and ISAS which is used for astronomy (space-VLBI). These networks operated in cooperation with NTT. In order to realize a virtual telescope, the acquired VLBI data were corrected via the ATM networks and were synthesized using the VLBI technique. The cross-correlation processing and data observation were done simultaneously in this system and radio flares on the weak radio source (HR1099) were detected.
  • K Sorai, K Sunada, SK Okumura, T Iwasa, A Tanaka, K Natori, H Onuki  RADIO TELESCOPES  4015-  86  -95  2000  [Not refereed][Not invited]
     
    New digital spectrometers for the 25-BEam Array Receiver System (BEARS) of the Nobeyama 45-m telescope are described. A commercial digital oscilloscope is used as a digitizer. The digitizer samples analogue data with 2 bits (4 levels). Data of 512 MHz bandwidth are processed for four beams at the same time. The data-formatting unit demultiplexes 2 bits 8 data in parallel to 32 parallels and sends outputs to LSIs. General purpose LSIs for autocorrelation read the digital data with a clock rate of 32 MHz. Thirty-two LSIs of 32 lags connected in cascades calculate 1024-lag autocorrelation, and output a 1024-channel power spectrum of 512 MHz bandwidth. The bandwidth of 32 MHz is achieved by picking up the data in a rate of 1/16 in the front part of the autocorrelator module. The total performances have been demonstrated by long-term integration of noise signals from receivers and observations of the Galactic star-forming region W51 in CO line.
  • K Sunada, C Yamaguchi, N Nakai, K Sorai, SK Okumura, N Ukita  RADIO TELESCOPES  4015-  237  -246  2000  [Not refereed][Not invited]
     
    A large focal plane array receiver system for the NRO 45m telescope ISIS 25-BEam array Receiver System, or BEARS) is described. This new array receiver uses SIS junctions and has 25 elements. It can operate at the frequency range of 82 - 116 GHz. The development of this new system is almost complete. We describe about the whole system in detail, which includes the receiver, the IF systems, the new spectrometers and the remote control systems. We also describe about the performances and the uniformity of the system and show the astronomical result.
  • K Sorai, K Sunada, SK Okumura, T Iwasa, A Tanaka, K Natori, H Onuki  RADIO TELESCOPES  4015-  86  -95  2000  [Not refereed][Not invited]
     
    New digital spectrometers for the 25-BEam Array Receiver System (BEARS) of the Nobeyama 45-m telescope are described. A commercial digital oscilloscope is used as a digitizer. The digitizer samples analogue data with 2 bits (4 levels). Data of 512 MHz bandwidth are processed for four beams at the same time. The data-formatting unit demultiplexes 2 bits 8 data in parallel to 32 parallels and sends outputs to LSIs. General purpose LSIs for autocorrelation read the digital data with a clock rate of 32 MHz. Thirty-two LSIs of 32 lags connected in cascades calculate 1024-lag autocorrelation, and output a 1024-channel power spectrum of 512 MHz bandwidth. The bandwidth of 32 MHz is achieved by picking up the data in a rate of 1/16 in the front part of the autocorrelator module. The total performances have been demonstrated by long-term integration of noise signals from receivers and observations of the Galactic star-forming region W51 in CO line.
  • K Sunada, C Yamaguchi, N Nakai, K Sorai, SK Okumura, N Ukita  RADIO TELESCOPES  4015-  237  -246  2000  [Not refereed][Not invited]
     
    A large focal plane array receiver system for the NRO 45m telescope ISIS 25-BEam array Receiver System, or BEARS) is described. This new array receiver uses SIS junctions and has 25 elements. It can operate at the frequency range of 82 - 116 GHz. The development of this new system is almost complete. We describe about the whole system in detail, which includes the receiver, the IF systems, the new spectrometers and the remote control systems. We also describe about the performances and the uniformity of the system and show the astronomical result.
  • Low Density Molecular Gas in the Galaxy
    Kumiko S. Usuda, Tetsuo Hasegawa, Toshihiro Handa, Jun-Ichi Morino, Tuyoshi Sawada, Seiichi Sakamoto, Tomoharu Oka, Masumichi Seta, Kazuo Sorai, Masahiko Hayashi, Roy Booth, Lars-Åke Nyman, Leonardo Bronfman, Jorge May, Abraham Luna, Peter Shaver, Glenn J. White  Proceedings of the 3rd Cologne-Zermatt Symposium, The Physics and Chemistry of the Interstellar Medium, edited by V. Ossenkopf, J. Stuzki, G. Winnewisser  96  1999  [Not refereed][Not invited]
  • The Tokyo-Nobeyama CO J=2-1 Galactic Plane Survey
    Seiichi Sakamoto, Tetsuo Hasegawa, Toshihiro Handa, Jun-Ichi Morino, Tomoharu Oka, Masumichi Seta, Kazuo Sorai, Kumiko S. Usuda, Masahiko Hayashi  ASP Conference Series 168, New Perspectives on the Interstellar Medium, editted by A. R. Taylor, T. L. Landecker, and G. Joncas  90  1999  [Not refereed][Not invited]
  • Molecular Gas in the Galactic Center: Large-Scale Structure and Kinematics
    Tsuyoshi Sawada, Tetsuo Hasegawa, Toshihiro Handa, Jun-Ichi Morino, Kumiko S. Usuda, Kazuo Sorai, Tomoharu Oka, Masumichi Seta, Seiichi Sakamoto, Masahiko Hayashi, Roy Booth, Leonard Bronfman, Abraham C. Luna, Lars-Åke Nyman  Proceedings Of Star Formation 1999, editted by T. Nakamoto and Nobeyama Radio Observatory  104  -105  1999  [Not refereed][Not invited]
  • A CO(J=2-1)line survey of the galactic center
    Tsuyoshi Sawada, Tetsuo Hasegawa, Toshihiro Handa, Kumiko S. Usuda, Jun-Ichi Morino, Roy Booth, Leonardo Bronfman, Abraham C. Luna, Masahiko Hayashi, Lars-Åke Nyman, Tomoharu Oka, Seiichi Sakamoto, Masumichi Seta, Peter Shaver, Kazuo Sorai  Advances in Space Research  23-  (5-6)  985  -989  1999  [Not refereed][Not invited]
  • Low Density Molecular Gas in the Galaxy
    Kumiko S. Usuda, Tetsuo Hasegawa, Toshihiro Handa, Jun-Ichi Morino, Tuyoshi Sawada, Seiichi Sakamoto, Tomoharu Oka, Masumichi Seta, Kazuo Sorai, Masahiko Hayashi, Roy Booth, Lars-Åke Nyman, Leonardo Bronfman, Jorge May, Abraham Luna, Peter Shaver, Glenn J. White  Proceedings of the 3rd Cologne-Zermatt Symposium, The Physics and Chemistry of the Interstellar Medium, edited by V. Ossenkopf, J. Stuzki, G. Winnewisser  96  1999  [Not refereed][Not invited]
  • The Tokyo-Nobeyama CO J=2-1 Galactic Plane Survey
    Seiichi Sakamoto, Tetsuo Hasegawa, Toshihiro Handa, Jun-Ichi Morino, Tomoharu Oka, Masumichi Seta, Kazuo Sorai, Kumiko S. Usuda, Masahiko Hayashi  ASP Conference Series 168, New Perspectives on the Interstellar Medium, editted by A. R. Taylor, T. L. Landecker, and G. Joncas  90  1999  [Not refereed][Not invited]
  • A CO(J=2-1)line survey of the galactic center
    Tsuyoshi Sawada, Tetsuo Hasegawa, Toshihiro Handa, Kumiko S. Usuda, Jun-Ichi Morino, Roy Booth, Leonardo Bronfman, Abraham C. Luna, Masahiko Hayashi, Lars-Åke Nyman, Tomoharu Oka, Seiichi Sakamoto, Masumichi Seta, Peter Shaver, Kazuo Sorai  Advances in Space Research  (23)  985  -989  1999  [Not refereed][Not invited]
  • Molecular Gas in the Galactic Center: Large-Scale Structure and Kinematics
    Tsuyoshi Sawada, Tetsuo Hasegawa, Toshihiro Handa, Jun-Ichi Morino, Kumiko S. Usuda, Kazuo Sorai, Tomoharu Oka, Masumichi Seta, Seiichi Sakamoto, Masahiko Hayashi, Roy Booth, Leonard Bronfman, Abraham C. Luna, Lars-Åke Nyman  Proceedings Of Star Formation 1999, editted by T. Nakamoto and Nobeyama Radio Observatory  104  -105  1999  [Not refereed][Not invited]
  • A CO(J=2-1)line survey of the galactic center
    Tsuyoshi Sawada, Tetsuo Hasegawa, Toshihiro Handa, Kumiko S. Usuda, Jun-Ichi Morino, Roy Booth, Leonardo Bronfman, Abraham C. Luna, Masahiko Hayashi, Lars-Åke Nyman, Tomoharu Oka, Seiichi Sakamoto, Masumichi Seta, Peter Shaver, Kazuo Sorai  Advances in Space Research  23-  (5-6)  985  -989  1999  [Not refereed][Not invited]
  • M Seta, T Hasegawa, TM Dame, S Sakamoto, T Oka, T Handa, M Hayashi, JI Morino, K Sorai, KS Usuda  ASTROPHYSICAL JOURNAL  505-  (1)  286  -298  1998/09  [Not refereed][Not invited]
     
    We present results of CO J = 2-1 line mapping of molecular clouds in the vicinity of the supernova remnants (SNRs) W44 and IC 443. Large areas spanning similar to 1.degrees 5 x 2 degrees were observed with the 9' beam of the University of Tokyo-Nobeyama Radio Observatory 60 cm Survey Telescope. We identified six giant molecular clouds (GMCs) with masses (0.3-3) x 10(5) M. around W44. Three show evidence of interaction with the SNR. In particular, one exhibits a line wing emission and an abrupt velocity shift at the position at which the cloud overlaps with the SNR. The CO J = 2-1/J = 1-0 line intensity ratio significantly exceeds unity (1.3) in the wing. In IC 443, a high-velocity line wing emission was detected in CO J = 2-1 with our 9' beam. The CO J = 2-1/J = 1-0 ratio is extremely high (>3) in the wing, which suggests that the emission comes from spatially extended optically thin (tau - 0.1), dense [n(H-2) similar to 10(5) cm(-3)], and warm (similar to 80 K) gas. W44 is established as a good example of an SNR interacting with GMCs, while IC 443 is in interaction with a low-mass dark cloud. The mass and kinetic energy of the shocked gas are, respectively, 1 x 10(3) M. and 4 x 10(48) ergs in W44, and 70 M. and 6 x 10(47) ergs in IC 443. A very high CO J = 2-1/J = 1-0 ratio in the line wings of a GMC may be a useful marker of interaction with an SNR. Such a marker would be extremely valuable for determining GMC-SNR associations in the inner Galaxy where numerous GMCs often lie along the line of sight. Such associations often provide the best means of determining SNR distances.
  • M Seta, T Hasegawa, TM Dame, S Sakamoto, T Oka, T Handa, M Hayashi, JI Morino, K Sorai, KS Usuda  ASTROPHYSICAL JOURNAL  505-  (1)  286  -298  1998/09  [Not refereed][Not invited]
     
    We present results of CO J = 2-1 line mapping of molecular clouds in the vicinity of the supernova remnants (SNRs) W44 and IC 443. Large areas spanning similar to 1.degrees 5 x 2 degrees were observed with the 9' beam of the University of Tokyo-Nobeyama Radio Observatory 60 cm Survey Telescope. We identified six giant molecular clouds (GMCs) with masses (0.3-3) x 10(5) M. around W44. Three show evidence of interaction with the SNR. In particular, one exhibits a line wing emission and an abrupt velocity shift at the position at which the cloud overlaps with the SNR. The CO J = 2-1/J = 1-0 line intensity ratio significantly exceeds unity (1.3) in the wing. In IC 443, a high-velocity line wing emission was detected in CO J = 2-1 with our 9' beam. The CO J = 2-1/J = 1-0 ratio is extremely high (>3) in the wing, which suggests that the emission comes from spatially extended optically thin (tau - 0.1), dense [n(H-2) similar to 10(5) cm(-3)], and warm (similar to 80 K) gas. W44 is established as a good example of an SNR interacting with GMCs, while IC 443 is in interaction with a low-mass dark cloud. The mass and kinetic energy of the shocked gas are, respectively, 1 x 10(3) M. and 4 x 10(48) ergs in W44, and 70 M. and 6 x 10(47) ergs in IC 443. A very high CO J = 2-1/J = 1-0 ratio in the line wings of a GMC may be a useful marker of interaction with an SNR. Such a marker would be extremely valuable for determining GMC-SNR associations in the inner Galaxy where numerous GMCs often lie along the line of sight. Such associations often provide the best means of determining SNR distances.
  • K Sorai, N Nakai, N Kuno, K Nishiyama  CENTRAL REGIONS OF THE GALAXY AND GALAXIES  141  -142  1998  [Not refereed][Not invited]
  • T Hasegawa, J Morino, T Sawada, T Handa, K Sato, T Oka, S Sakamoto, K Sorai, M Seta, M Hayashi, L Bronfman, J May, R Booth, LA Nyman, P Shaver  CENTRAL REGIONS OF THE GALAXY AND GALAXIES  179  -180  1998  [Not refereed][Not invited]
  • N Kuno, N Nakai, K Nishiyama, K Sorai, T Handa, T Iga  CENTRAL REGIONS OF THE GALAXY AND GALAXIES  243  -244  1998  [Not refereed][Not invited]
  • A 500-MHz Acousto-optical Spectrometer for the Nobeyama 45-m radio telescope
    Kazuo Sorai, Kohta Nishiyama, Tetsuo Hasegawa, Takeshi Miyaji, Nobuharu Ukita  Nobeyama Radio Observatory Technical Report  1  -10  1998  [Not refereed][Not invited]
  • K Sorai, N Nakai, N Kuno, K Nishiyama  CENTRAL REGIONS OF THE GALAXY AND GALAXIES  141  -142  1998  [Not refereed][Not invited]
  • T Hasegawa, J Morino, T Sawada, T Handa, K Sato, T Oka, S Sakamoto, K Sorai, M Seta, M Hayashi, L Bronfman, J May, R Booth, LA Nyman, P Shaver  CENTRAL REGIONS OF THE GALAXY AND GALAXIES  179  -180  1998  [Not refereed][Not invited]
  • N Kuno, N Nakai, K Nishiyama, K Sorai, T Handa, T Iga  CENTRAL REGIONS OF THE GALAXY AND GALAXIES  243  -244  1998  [Not refereed][Not invited]
  • A 500-MHz Acousto-optical Spectrometer for the Nobeyama 45-m radio telescope
    Kazuo Sorai, Kohta Nishiyama, Tetsuo Hasegawa, Takeshi Miyaji, Nobuharu Ukita  Nobeyama Radio Observatory Technical Report  1  -10  1998  [Not refereed][Not invited]
  • The CO 2-1/1-0 Ratio in the Southern Milky Way and the Large Magellanic Cloud
    Tetsuo Hasegawa, Jun Ichi Morino, Kazuo Sorai, Toshihiro Handa, Kumiko Sato, Tomoharu Oka, Masumichi Seta, Seiichi Sakamoto, Masahiko Hayashi, Roy Booth, Lars-Åke Nyman, Leonardo Bronfman, Monica Rubio, Peter Shaver  ASP Conference Series, Diffuese Infrared Radiation and the IRTS  124-  244  1997  [Not refereed][Not invited]
  • 12CO (J = 2-1) emission in the inner galaxy
    Kazuo Sorai, Tetsuo Hasegawa, Toshihiro Handa, Seiichi Sakamoto, Tomoharu Oka, Masamichi Seta, Kumiko Sato, Jun Ichi Morino, Masahiko Hayashi, Hiroko Shinnaga  IAU Symposium No.170, CO:Twenty-five Years of Millimeter-wave Spectroscopy  463  1997  [Not refereed][Not invited]
  • S Sakamoto, T Handa, Y Sofue, M Honma, K Sorai  ASTROPHYSICAL JOURNAL  475-  (1)  134  -143  1997/01  [Not refereed][Not invited]
     
    We present high-resolution simultaneous observations of the edge-on galaxy NGC 891 in (CO)-C-12 and (CO)-C-13 emissions. The molecular thin-disk component within 10.7 kpc from the galactic center was completely covered. This data set with accurate relative calibrations of intensity scale and pointing is analyzed to examine radial variation in the physical properties of the molecular gas. The total (CO)-C-13/(CO)-C-12 luminosity ratio is 1/6.6. A low (CO)-C-13/(CO)-C-12 intensity ratio of 1/(15.4 +/- 6.0) is observed in the nuclear disk of about 550 pc in radius. There exists a systematic gradient of the (CO)-C-13/(CO)-C-12 intensity ratio in the main galactic disk as a function of galactocentric distance: the (CO)-C-13/(CO)-C-12 intensity ratio exhibits a notable peak of similar or equal to 1/4.5 near 4 kpc, and decreases systematically outward down to less than or similar to 1/10 at 10 kpc. The observational results are analyzed on the basis of a CO excitation analysis. The low (CO)-C-13/(CO)-C-12 intensity ratio in the nuclear disk may be attributed to a predominance of warm molecular gas (greater than or similar to 40 K) of moderate gas density (similar to 10(3) cm(-3)), while the systematic gradient of the (CO)-C-13/(CO)-C-12 intensity ratio in the main disk can be interpreted in terms of radial decrease in the dense molecular gas fraction. Since interstellar gas in the inner part of the galaxy is mostly molecular, this variation will be ascribed to compression of molecular gas with its strength dependent on galactocentric distance rather than dissociation of low-density molecular gas by UV photons from young stars in the inner part of the galaxy.
  • The CO 2-1/1-0 Ratio in the Southern Milky Way and the Large Magellanic Cloud
    Tetsuo Hasegawa, Jun Ichi Morino, Kazuo Sorai, Toshihiro Handa, Kumiko Sato, Tomoharu Oka, Masumichi Seta, Seiichi Sakamoto, Masahiko Hayashi, Roy Booth, Lars-Åke Nyman, Leonardo Bronfman, Monica Rubio, Peter Shaver  ASP Conference Series, Diffuese Infrared Radiation and the IRTS  124-  244  1997  [Not refereed][Not invited]
  • 12CO(J=2-1)Emission in the Inner Galaxy
    Kazuo Sorai, Tetsuo Hasegawa, Toshihiro Handa, Seiichi Sakamoto, Tomoharu Oka, Masamichi Seta, Kumiko Sato, Jun Ichi Morino, Masahiko Hayashi, Hiroko Shinnaga  IAU Symposium No.170, CO:Twenty-five Years of Millimeter-wave Spectroscopy  463  1997  [Not refereed][Not invited]
  • S Sakamoto, T Handa, Y Sofue, M Honma, K Sorai  ASTROPHYSICAL JOURNAL  475-  (1)  134  -143  1997/01  [Not refereed][Not invited]
     
    We present high-resolution simultaneous observations of the edge-on galaxy NGC 891 in (CO)-C-12 and (CO)-C-13 emissions. The molecular thin-disk component within 10.7 kpc from the galactic center was completely covered. This data set with accurate relative calibrations of intensity scale and pointing is analyzed to examine radial variation in the physical properties of the molecular gas. The total (CO)-C-13/(CO)-C-12 luminosity ratio is 1/6.6. A low (CO)-C-13/(CO)-C-12 intensity ratio of 1/(15.4 +/- 6.0) is observed in the nuclear disk of about 550 pc in radius. There exists a systematic gradient of the (CO)-C-13/(CO)-C-12 intensity ratio in the main galactic disk as a function of galactocentric distance: the (CO)-C-13/(CO)-C-12 intensity ratio exhibits a notable peak of similar or equal to 1/4.5 near 4 kpc, and decreases systematically outward down to less than or similar to 1/10 at 10 kpc. The observational results are analyzed on the basis of a CO excitation analysis. The low (CO)-C-13/(CO)-C-12 intensity ratio in the nuclear disk may be attributed to a predominance of warm molecular gas (greater than or similar to 40 K) of moderate gas density (similar to 10(3) cm(-3)), while the systematic gradient of the (CO)-C-13/(CO)-C-12 intensity ratio in the main disk can be interpreted in terms of radial decrease in the dense molecular gas fraction. Since interstellar gas in the inner part of the galaxy is mostly molecular, this variation will be ascribed to compression of molecular gas with its strength dependent on galactocentric distance rather than dissociation of low-density molecular gas by UV photons from young stars in the inner part of the galaxy.
  • A 12CO(J=2-1)Survey of the First Quadrant of the Galaxy
    Kazuo Sorai, Seiichi Sakamoto, Tetsuo hasegawa, Toshihiro Handa, Masahiko hayashi, Tomoharu Oka, Masumichi Seta, Kumiko Sato, Sato Hiroko Shinnagam, Jun Ichi Morino  Proceedings of Third East-Asian Meeting on Astronomy, Ground-Based Astronomu in Asia, edited by Norio Kaifu  115  -120  1996  [Not refereed][Not invited]
  • A 12CO(J=2-1)Survey of the First Quadrant of the Galaxy
    Kazuo Sorai, Seiichi Sakamoto, Tetsuo hasegawa, Toshihiro Handa, Masahiko hayashi, Tomoharu Oka, Masumichi Seta, Kumiko Sato, Sato Hiroko Shinnagam, Jun Ichi Morino  Proceedings of Third East-Asian Meeting on Astronomy, Ground-Based Astronomu in Asia, edited by Norio Kaifu  115  -120  1996  [Not refereed][Not invited]

Research Grants & Projects

  • Kinematics and Star Formation in the Galaxy
    Date (from‐to) : 2001 -2008
  • Molecular Gas and Star Formation in Barred Spiral Galaxies
    Cooperative Research
    Date (from‐to) : 2003 -2004

Educational Activities

Teaching Experience

  • Astrophysics 1
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 銀河,観測天文学
  • Astrophysics
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 星形成、分子雲、放射過程、自己重力系、恒星・恒星進化
  • Modern Astronomy
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 天文学,天体と天体現象,宇宙物理学
  • Physics I
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 運動、力、運動の法則、仕事、エネルギー、運動量、保存則、剛体、流体、単振動、音と光、干渉、回折
  • Special Lectures for Modern Physics
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 光学赤外線天文学,撮像装置,分光装置,信号雑音比,超新星,銀河,宇宙背景放射,観測的宇宙論,ダークエネルギー


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