Nario Kuno

Osaka Prefecture University, Sakai, Ōsaka, Japan

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Publications (164)260.59 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS ($J_N=4_3-3_2$), HC$_3$N ($J=5-4$), N$_2$H$^+$ ($J=1-0$), and SiO ($J=2-1, v=0$) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely-strong CCS emission is detected. The CCS-to-N$_2$H$^+$ abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different $V_{\rm LSR}$. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few $\times \ 10^5$ yr because CCS is abundant only in such a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is $0.4 \times \ 10^5$ yr, is extremely high as about 70 percent in the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.
    The Astrophysical Journal Letters 07/2014; 791(2). · 6.35 Impact Factor
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    ABSTRACT: We present evidence that super giant H II regions (GHRs) and other disk regions of the nearby spiral galaxy, M33, occupy distinct locations in the correlation between molecular gas, , and the star formation rate surface density, ΣSFR. This result is based on wide-field and high-sensitivity CO(3-2) observations at 100 pc resolution. Star formation efficiencies (SFEs), defined as , in GHRs are found to be ~1 dex higher than in other disk regions. The CO(3-2)/CO(1-0) integrated intensity ratio, R 3-2/1-0, is also higher than the average over the disk. Such high SFEs and R 3-2/1-0 can reach the values found in starburst galaxies, which suggests that GHRs may be the elements building up a larger-scale starburst region. Three possible contributions to high SFEs in GHRs are investigated: (1) the I CO-N(H2) conversion factor, (2) the dense gas fraction traced by R 3-2/1-0, and (3) the initial mass function (IMF). We conclude that these starburst-like properties in GHRs can be interpreted by a combination of both a top-heavy IMF and a high dense gas fraction, but not by changes in the I CO-N(H2) conversion factor.
    The Astrophysical Journal 06/2014; 788(2):167. · 6.73 Impact Factor
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    ABSTRACT: We present evidence that super giant HII regions (GHRs) and other disk regions of the nearby spiral galaxy, M33, occupy distinct locations in the correlation between molecular gas, $\Sigma_{\rm H_2}$, and the star formation rate surface density, $\Sigma_{\rm SFR}$. This result is based on wide field and high sensitivity CO(3-2) observations at 100 pc resolution. Star formation efficiencies (SFE), defined as $\Sigma_{\rm SFR}$/$\Sigma_{\rm H_2}$, in GHRs are found to be about 1 dex higher than in other disk regions. The CO(3-2)/CO(1-0) integrated intensity ratio is also higher than the average over the disk. Such high SFE and CO(3-2)/CO(1-0) can reach the values found in starburst galaxies, which suggests that GHRs may be the elements building up a larger scale starburst region. Three possible contributions to high SFEs in GHR are investigated: (1) the $I_{CO}$-$N({\rm H_2})$ conversion factor, (2) the dense gas fraction traced by CO(3-2)/CO(1-0), and (3) the initial mass function (IMF). We conclude that these starburst-like properties in GHRs can be interpreted by a combination of both a top-heavy IMF and a high dense gas fraction, but not by changes in the $I_{CO}$-$N({\rm H_2})$ conversion factor.
    05/2014;
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    ABSTRACT: We present evidence that super giant HII regions (GHRs) and other disk regions of the nearby spiral galaxy, M33, occupy distinct locations in the correlation between molecular gas, $\Sigma_{\rm H_2}$, and the star formation rate surface density, $\Sigma_{\rm SFR}$. This result is based on wide field and high sensitivity CO(3-2) observations at 100 pc resolution. Star formation efficiencies (SFE), defined as $\Sigma_{\rm SFR}$/$\Sigma_{\rm H_2}$, in GHRs are found to be about 1 dex higher than in other disk regions. The CO(3-2)/CO(1-0) integrated intensity ratio is also higher than the average over the disk. Such high SFE and CO(3-2)/CO(1-0) can reach the values found in starburst galaxies, which suggests that GHRs may be the elements building up a larger scale starburst region. Three possible contributions to high SFEs in GHR are investigated: (1) the $I_{CO}$-$N({\rm H_2})$ conversion factor, (2) the dense gas fraction traced by CO(3-2)/CO(1-0), and (3) the initial mass function (IMF). We conclude that these starburst-like properties in GHRs can be interpreted by a combination of both a top-heavy IMF and a high dense gas fraction, but not by changes in the $I_{CO}$-$N({\rm H_2})$ conversion factor.
    04/2014;
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    ABSTRACT: We present the results of the wide-field 12CO(1-0) observations of the nearby barred galaxy M 83 carried out with the Nobeyama Millimeter Array (NMA). The interferometric data are combined with the data obtained with the Nobeyama 45 m telescope to recover the total flux. The target fields of the observations cover the molecular bar and part of the spiral arms, with a spatial resolution of ̃ 110 pc × 260 pc. By exploiting the resolution and sensitivity to extended CO emission, the impact of the galactic structures on the molecular gas content is investigated in terms of the gas kinematics and the star formation. By inspecting the gas kinematics, the pattern speed of the bar is estimated to be 57.4 ± 2.8 km s-1 kpc-1, which places the corotation radius at about 1.7 times the semi-major radius of the bar. Within the observed field, H II regions brighter than 1037.6 erg s-1 in Hα luminosity are found to be preferentially located downstream of the CO-emitting regions. Azimuthal angular offsets between molecular gas and star forming (SF) calculated with the angular cross-correlation method confirm the trend. By comparing with a cloud orbit model based on the derived pattern speed, the angular offsets are found to be in accordance with a time delay of about 10 Myr. Finally, to test whether the arm/bar promote star formation efficiency [SFE ≡ Star Formation Rate (SFR)/H2 mass], SFR is derived with the diffuse-background-subtracted Hα and 24 μm images. The arm-to-interarm ratio of the SFE is found to lie in the range of 2 to 5, while it is ̃ 1 if no background removal is performed. The CO-SF offsets and the enhancement of the SFE in the arm/bar found in the inner region of M 83 are in agreement with the predictions of the classical galactic shock model.
    04/2014;
  • Y. Miyamoto, N. Nakai, N. Kuno
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    ABSTRACT: The evolution of Giant Molecular Clouds (GMCs) and Giant Molecular Associations (GMAs) is one of the keys to understand massive star formation in a galaxy and hence evolution of the galaxy. It has been considered that GMCs and GMAs are formed in spiral arms. Recently, however, GMCs are found not only in the spiral arms but also in the inter-arms. It is suggested that the GMCs in the inter-arms might be formed by the shear motion. However, the relation between molecular clouds and the kinetic shear motion in the clouds is still speculation, because the kinetic shear has not been directly measured in a galaxy. We have investigated the dynamics of the molecular gas and the evolution of GMAs in the spiral galaxy M51 with the NRO 45-m telescope. The velocity components of the molecular gas perpendicular and parallel to the spiral arms were derived at each spiral phase from the distribution of the line-of-sight velocity of the CO gas. The shear motion in the galactic disk was determined from the velocity vectors at each spiral phase. It was revealed that the distributions of the shear strength and of GMAs are anti-correlated. In addition, GMAs can grow up just in regions where the gravitational critical density is larger than the critical shear density. This result suggests that the evolution of GMAs is heavily affected by the shear.
    02/2014;
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    Y. Miyamoto, N. Nakai, N. Kuno
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    ABSTRACT: We have investigated the dynamics of the molecular gas and the evolution of GMAs in the spiral galaxy M51 with the NRO 45-m telescope. The velocity components of the molecular gas perpendicular and parallel to the spiral arms are derived at each spiral phase from the distribution of the line-of-sight velocity of the CO gas. In addition, the shear motion in the galactic disk is determined from the velocity vectors at each spiral phase. It is revealed that the distributions of the shear strength and of GMAs are anti-correlated. GMAs exist only in the area of the weak shear strength and further on the upstream side of the high shear strength. GMAs and most of GMCs exist in the regions where the shear critical surface density is smaller than the gravitational critical surface density, indicating that they can stably grow by self-gravity and the collisional agglomeration of small clouds without being destroyed by shear motion. These indicate that the shear motion is an important factor in evolution of GMCs and GMAs.
    11/2013;
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    Hsi-An Pan, Nario Kuno, Akihiko Hirota
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    ABSTRACT: The Kennicutt-Schmidt (K--S) law in IC 342 is examined using the 12CO-to-H2 conversion factor (Xco,v), which depends on the metallicity and CO intensity. Additionally, an optically thin 13CO (1-0) is also independently used to analyze the K--S law. Xco,v is two to three times lower than the Galactic standard Xco in the galactic center and approximately two times higher than Xco at the disk. The surface densities of molecular gas (Sigma_H2) derived from 12CO and 13CO are consistent at the environment in a high-Sigma_H2 region. By comparing the K-S law in the disk and the central regions of IC 342, we found that the power law index of K-S law (N) increases toward the central region. Furthermore, the dependence of N on Sigma_H2 is observed. Specifically, N increases with Sigma_H2. The derived N in this work and previous observations are consistent with the implication that star formation is likely triggered by gravitational instability in the disk (low-Sigma_H2 region) of IC 342 and both gravitational instability and cloud-cloud collisions in the central region (high-Sigma_H2 regime). In addition, the increasing N toward the high-Sigma_H2 domain also matches the theoretical prediction regarding the properties of giant molecular clouds. The results of IC 342 are supported by the same analysis of other nearby galaxies.
    11/2013; 66(1).
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    ABSTRACT: We are developing a new dual polarization receiver at 45GHz band to be installed on the Nobeyama 45 m radio telescope. The purpose of the receiver is to measure the polarization difference caused by the Zeeman effect in magnetized molecular cores, and then we are focusing on the stability of the polarization observations for the development. The magnetic field is considered to play an important role in a star formation process. However, our understanding of the magnetic field in molecular clouds/cores is still very limited, because the measurement of the magnetic field has been quite difficult as it requires very sensitive, stable receiver system. We then plan to develop a new receiver system for measuring the Zeeman effect, and the details about the project is described by Nakamura et al. in this volume. In this presentation, we focus on the development of the new dual polarization receiver.
    10/2013;
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    ABSTRACT: We observed nine barred spiral galaxies at z ˜ 0.1-0.2 in CO(J=1-0) with the 45-m telescope at the Nobeyama Radio Observatory in 2010-2011 and successfully detected emissions from seven galaxies including tentative detections. The molecular gas fraction of our samples are systematically higher than the ones of local barred galaxies as well as the expected upper-limit where the bars can be formed or survive in numerical simulations. This implies that the simulations of bar formation and evolution may need a little corrections and the formation and evolution of bars must be considered in the context of the galactic disk evolution and formation, i.e., bar formation in gas-rich disks.
    10/2013;
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    ABSTRACT: We performed 12CO(J = 1-0) mapping observations toward four interacting galaxies in early and mid stages of the interaction using the 45-m telescope. Comparing to isolated galaxies whose data were also obtained with the 45-m, we found that interacting galaxies have (1) lower degree of the central concentration of molecular gas, (2) high molecular gas fraction (the mass of molecular gas to the sum of the mass of molecular gas and atomic gas ratio) and (3) no difference in Kennicutt-Schmidt law.
    10/2013;
  • Y. Miyamoto, N. Nakai, N. Kuno
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    ABSTRACT: Understanding of the evolution of Giant Molecular Associations (GMAs) is important to improve our knowledge about massive star formation and galaxy evolution. We have investigated the dynamics of the molecular gas and the evolution of GMAs in the spiral galaxy M51 with the NRO 45-m telescope. The velocity components of the molecular gas perpendicular and parallel to the spiral arms were derived at each spiral phase from the distribution of the line-of-sight velocity of the CO gas. In addition, the shear motion in the galactic disk was determined from the velocity vectors at each spiral phase. It was revealed that the distributions of the shear strength and of GMAs are anti-correlation each other. This result suggests that the GMAs are destructed into GMCs by the strong shear, although surviving in the weak shear.
    10/2013;
  • 10/2013;
  • 10/2013;
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    ABSTRACT: We present the results of the CO-line mapping observations of the local group galaxy M33 as part of the NRO legacy project, NRO M33 All-Disk Survey of Giant Molecular Clouds (NRO MAGiC). The observations were performed using the 45-m telescope of the Nobeyama Radio Observatory and the ASTE 10-m telescope. We find that the star formation rate have very wide range of 109-106 M⊙ yr-1pc-2 among GMCs, while 12CO(J=1-0) intensity is nearly constant. This indicates that the Schmidt-Kenicutt law becomes invalid for the scale of GMCs (˜80pc). We identify 74 major GMCs in the observing field of ASTE from the 12CO(J=1-0) data, and detected 12CO(J=3-2) emission in 65 GMCs among them. We find that the correlation between the 12CO(J=3-2) intensity and the star formation rate still holds at the scale of GMCs. This result show that the star-forming activity is closely associated with warm and dense gases that are traced with the 12CO(J=3-2) line, even in the scale of GMCs. We also find that the GMCs with a high star-forming activity tend to show a high integrated intensity ratio R3-2/1-0. Moreover, we also observe a mass-dependent trend of R3-2/1-0 for the GMCs with a low star-forming activity. From these results, we speculate that the R3-2/1-0 values of the GMCs with a low star-forming activity mainly depend on the dense gas fraction and not on the temperature, and therefore, the dense gas fraction increases with the mass of GMCs, at least in the GMCs with a low star-forming activity.
    10/2013;
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    ABSTRACT: Stars form out of dense cores in turbulent, magnetized molecular clouds. However, the role of magnetic fields in star formation remains poorly understood both theoretically and observationally. This is in part due to the lack of the observational characterization of the magnetic fields that are associated with the dense cores prior to star formation, or pre-protostellar cores. To shed light on the issue of the magnetic field in the gravitational collapse of pre-protostellar cores, we have started a project of the magnetic field measurements toward pre-protostellar cores using the Zeeman splitting of CCS (JN = 43 - 32) line. We are now developing a new 45GHz band, dual polarization, reciever for the Nobeyama 45m telescope. In this contribution, we summarize a current status of our Zeeman project and future plan.
    10/2013;
  • N. Kuno
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    ABSTRACT: We present the results of the NRO legacy project “M33 All Disk Survey of Giant Molecular Clouds (NRO-MAGiC)”. We discuss the following topics using CO(1-0), CO(3-2), and 1.1 mm continuum data obtained with NRO 45-m and ASTE 10-m telescopes: formation of molecular gas, relation between molecular gas and star formation, evolution of giant molecular clouds, and radial gradient of dust temperature. We also present the preliminary results of the ALMA Cycle0 observations of M83.
    10/2013;
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    ABSTRACT: We present results of 12CO(J = 1-0) observations using NRO 45m radio telescope toward four interacting galaxies in the early and the mid stage of the interaction (Arp 84, VV 219, VV 254 and the Antennae Galaxies). We obtain central concentration of molecular gas and find interacting galaxies in the early and the mid stage have lower gas concentration toward the nuclei compared to isolated galaxies. We find molecular gas fraction in interacting galaxies is higher than isolated galaxies. With model fitting, this high molecular gas fraction is owing to high external pressure induced by the interaction. We also examine the relation between star formation rate and the surface density of interstellar gas (the sum of molecular and atomic hydrogen gas) resolving galactic structures. The relation is same as isolated galaxies, which suggests that high molecular gas fraction does not connect directly to the active star forming activity in interacting galaxies.
    10/2013;
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    ABSTRACT: We report a super-linear correlation for the star formation law based on new CO($J$=1-0) data from the CARMA and NOBEYAMA Nearby-galaxies (CANON) CO survey. The sample includes 10 nearby spiral galaxies, in which structures at sub-kpc scales are spatially resolved. Combined with the star formation rate surface density traced by H$\alpha$ and 24 $\mu$m images, CO($J$=1-0) data provide a super-linear slope of $N$ = 1.3. The slope becomes even steeper ($N$ = 1.8) when the diffuse stellar and dust background emission is subtracted from the H$\alpha$ and 24 $\mu$m images. In contrast to the recent results with CO($J$=2-1) that found a constant star formation efficiency (SFE) in many spiral galaxies, these results suggest that the SFE is not independent of environment, but increases with molecular gas surface density. We suggest that the excitation of CO($J$=2-1) is likely enhanced in the regions with higher star formation and does not linearly trace the molecular gas mass. In addition, the diffuse emission contaminates the SFE measurement most in regions where star formation rate is law. These two effects can flatten the power law correlation and produce the apparent linear slope. The super linear slope from the CO($J$=1-0) analysis indicates that star formation is enhanced by non-linear processes in regions of high gas density, e.g., gravitational collapse and cloud-cloud collisions.
    The Astrophysical Journal Letters 06/2013; 772(1). · 6.35 Impact Factor
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    ABSTRACT: We resolve 182 individual giant molecular clouds (GMCs) larger than 2.5 $\times$ 10$^{5}$ \Msun in the inner disks of five large nearby spiral galaxies (NGC 2403, NGC 3031, NGC 4736, NGC 4826, and NGC 6946) to create the largest such sample of extragalactic GMCs within galaxies analogous to the Milky Way. Using a conservatively chosen sample of GMCs most likely to adhere to the virial assumption, we measure cloud sizes, velocity dispersions, and $^{12}$CO (J=1-0) luminosities and calculate cloud virial masses. The average conversion factor from CO flux to H$_{2}$ mass (or \xcons) for each galaxy is 1-2 \xcounits, all within a factor of two of the Milky Way disk value ($\sim$2 \xcounits). We find GMCs to be generally consistent within our errors between the galaxies and with Milky Way disk GMCs; the intrinsic scatter between clouds is of order a factor of two. Consistent with previous studies in the Local Group, we find a linear relationship between cloud virial mass and CO luminosity, supporting the assumption that the clouds in this GMC sample are gravitationally bound. We do not detect a significant population of GMCs with elevated velocity dispersions for their sizes, as has been detected in the Galactic center. Though the range of metallicities probed in this study is narrow, the average conversion factors of these galaxies will serve to anchor the high metallicity end of metallicity-\xco trends measured using conversion factors in resolved clouds; this has been previously possible primarily with Milky Way measurements.
    The Astrophysical Journal 05/2013; 772(2). · 6.73 Impact Factor

Publication Stats

947 Citations
260.59 Total Impact Points

Institutions

  • 2014
    • Osaka Prefecture University
      • Department of Physical Science
      Sakai, Ōsaka, Japan
  • 1996–2014
    • The Graduate University for Advanced Studies
      • Department of Astronomical Science
      Миура, Kanagawa, Japan
  • 2013
    • Japan Aerospace Exploration Agency
      • Institute of Space and Astronautical Science (ISAS)
      Chōfu, Tōkyō, Japan
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 2012
    • Joetsu University of Education
      Niahi-niigata, Niigata, Japan
  • 2007–2011
    • National Astronomical Observatory of Japan
      • Astronomy Data Center
      Edo, Tōkyō, Japan
  • 2008
    • University of Tsukuba
      Tsukuba, Ibaraki, Japan
  • 1993–2008
    • Tohoku University
      • Astronomical Institute
      Japan
  • 2001
    • The University of Arizona
      Tucson, Arizona, United States
  • 1998
    • Hosei University
      Edo, Tōkyō, Japan
  • 1995
    • The University of Tokyo
      • Department of Astronomy
      Edo, Tōkyō, Japan