Nario Kuno

University of Tsukuba, Tsukuba, Ibaraki, Japan

Are you Nario Kuno?

Claim your profile

Publications (187)290.29 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of CO(J = 3–2) on-the-fly mappings of two nearby non-barred spiral galaxies, NGC 628 and NGC 7793, 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 ($L^{\prime }_{\rm CO(3-2)}$) and infrared (IR) luminosities (LIR) for NGC 628, NGC 7793, and M 83, and compared it with global luminosities of a JCMT (James Clerk Maxwell Telescope) Nearby Galaxy Legacy Survey sample. We found a striking linear $L^{\prime }_{\rm CO(3-2)}$–LIR 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 extinction-corrected star formation rates (SFRs) for NGC 628, NGC 7793, and M 83, and compared it with that for Giant Molecular Clouds in M 33 and 14 nearby galaxy centers. We found a linear ICO(3–2)–SFR correlation with ∼1 dex scatter. We conclude that the CO(J = 3–2) star-formation law (i.e., linear $L^{\prime }_{\rm CO(3-2)}$–LIR 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 ∼1 dex scatter.
    No preview · Article · Dec 2015 · Publications- Astronomical Society of Japan
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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. High-resolution image (100 pc) of $^{13}$CO (1-0) is created by single dish NRO45 and interferometer CARMA for the inner 2 kpc disk, which includes 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. Physical properties of molecular gas are inferred by (1) the Large Velocity Gradient (LVG) calculations using our observations and archival $^{12}$CO (1-0), $^{12}$CO(2-1) data, (2) dense gas fraction suggested by HCN to $^{12}$CO (1-0) luminosity ratio, and (3) infrared color. The results show that the molecular gas in the central region is warmer and denser than that of the offset ridges. Dense gas fraction of the central region is similar with that of LIRGs/ULIRGs, while 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. Star formation efficiency (SFE) changes by ~ 5 times in the inner disk. The variation of SFE agrees with the prediction in terms of star formation regulated by galactic bar. We find a consistency between star-forming region and the temperature inferred by the infrared color, suggesting that the distribution of sub-kpc scale temperature is driven by star formation.
    Preview · Article · Nov 2015 · The Astrophysical Journal
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We developed a dual-linear-polarization HEMT (High Electron Mobility Transistor) amplifier receiver system of the 45-GHz band (hereafter Z45), and installed it in the Nobeyama 45-m radio telescope. The receiver system is designed to conduct polarization observations by taking the cross correlation of two linearly-polarized components, from which we process full-Stokes spectroscopy. We aim to measure the magnetic field strength through the Zeeman effect of the emission line of CCS ($J_N=4_3-3_2$) toward pre-protostellar cores. A linear-polarization receiver system has a smaller contribution of instrumental polarization components to the Stokes $V$ spectra than that of the circular polarization system, so that it is easier to obtain the Stokes $V$ spectra. The receiver has an RF frequency of 42 $-$ 46 GHz and an intermediate frequency (IF) band of 4$-$8 GHz. The typical noise temperature is about 50 K, and the system noise temperature ranges from 100 K to 150K over the frequency of 42 $-$ 46 GHz. The receiver system is connected to two spectrometers, SAM45 and PolariS. SAM45 is a highly flexible FX-type digital spectrometer with a finest frequency resolution of 3.81 kHz. PolariS is a newly-developed digital spectrometer with a finest frequency resolution of 60 Hz, having a capability to process the full-Stokes spectroscopy. The Half Power Beam Width (HPBW) of the beam was measured to be 37$"$ at 43 GHz. The main beam efficiency of the Gaussian main beam was derived to be 0.72 at 43 GHz. The SiO maser observations show that the beam pattern is reasonably round at about 10 \% of the peak intensity and the side-lobe level was less than 3 \% of the peak intensity. Finally, we present some examples of astronomical observations using Z45.
    Full-text · Article · Sep 2015 · Publications- Astronomical Society of Japan
  • Hsi-An Pan · Nario Kuno · Kazuo Sorai · Michiko Umei
    [Show abstract] [Hide abstract]
    ABSTRACT: We used multi-wavelength analysis of the newly observed molecular gas (12CO and 13CO (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 NGC 5430 and its satellite embedded in the bar. Morphology of the molecular gas in the bar of NGC 5430 shows minimal signs of recent interactions in 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 NGC 5430 and its satellite collided several Gyr ago. History of star formation was constrained by using SFRs that trace different timescales (infrared, radio continuum, and H-alpha). 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 35 Msun/yr. 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 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 (LVG) calculations. The initial mass ratio of the NGC 5430 and its satellite are suggested to be in the intermediate ratio range of 7:1-20:1.
    No preview · Article · Aug 2015 · Publications- Astronomical Society of Japan
  • Kana Morokuma · Junichi Baba · Kazuo Sorai · Nario Kuno
    [Show abstract] [Hide abstract]
    ABSTRACT: We found stellar mass-dependent evolution of galactic molecular gas fractions (\$f_{\rm mol}=\frac{M_{\rm mol}}{M_\star+M_{\rm mol}}\$, Mmol: molecular gas mass, M*: stellar mass) where less massive galaxies have decreased fmol from z = 1 whereas massive galaxies have already had low fmol until z = 1. Comparison of the observed quantities (fmol, optical and near infra-red [NIR] colors, specific star formation rate [sSFR = SFR/M*]) with mass evolution models suggests that less massive galaxies had high fmol at z = 1 thanks to recent gas accretion.
    No preview · Article · Jul 2015 · Proceedings of the International Astronomical Union
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We performed 12CO(J=1-0) (hereafter, CO) observations towards 12 normal star-forming galaxies with stellar mass of Mstar=10^10.6-10^11.3 Msun at z=0.1-0.2 with the 45-m telescope at the Nobeyama Radio Observatory (NRO). The samples are selected with Dn(4000) that is a strength of the 4000 \AA break, instead of commonly used far-infrared (FIR) flux. We successfully detect the CO emissions from eight galaxies with signal-to-noise ratio (S/N) larger than three, demonstrating the effectiveness of the Dn(4000)-based sample selection. For the first time, we find a tight anti-correlation between Dn(4000) and molecular gas fraction (fmol) 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~0.1-0.2 also follow the same relation of nearby galaxies. This implies that the galaxies evolve along this Dn(4000)-fmol relation, and that Dn(4000) seems 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 Dn(4000) and non-zero gas fraction.
    Preview · Article · Jan 2015 · Publications- Astronomical Society of Japan
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have developed a software-based polarization spectrometer, PolariS, to acquire full-Stokes spectra with a very high spectral resolution of 61 Hz. The primary aim of PolariS is to measure the magnetic fields in dense star-forming cores by detecting the Zeeman splitting of molecular emission lines. The spectrometer consists of a commercially available digital sampler and a Linux computer. The computer is equipped with a graphics processing unit (GPU) to process FFT and cross-correlation using the CUDA (Compute Unified Device Architecture) library developed by NVIDIA. Thanks to a high degree of precision in quantization of the analog-to-digital converter and arithmetic in the GPU, PolariS offers excellent performances in linearity, dynamic range, sensitivity, bandpass flatness and stability. The software has been released under the MIT License and is available to the public. In this paper, we report the design of PolariS and its performance verified through engineering tests and commissioning observations.
    Full-text · Article · Dec 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated properties of interstellar medium in interacting galaxies in early and mid stages using mapping data of 12CO(J =1-0) and HI. Total gas mass (a sum of atomic and molecular gas mass) in interacting galaxies slightly reduced with large dispersion in the comparison with field galaxies. We found that molecular gas mass is enhanced in interacting galaxies assuming the standard CO-H2 conversion factor, while atomic gas mass is reduced. These results are reinforced by the fact that interacting galaxies have higher molecular gas fraction (fmol), a ratio of the surface density of molecular gas to that of total gas, (0.71 +- 0.15) than isolated galaxies (0.52 +- 0.18) and this indicates that an efficient transition from atomic gas to molecular gas is induced by the interaction. Isolated spiral galaxies show monotonically and gradually increase of fmol along the surface density of total gas. Contrary to isolated galaxies, interacting galaxies show high fmol (>0.8) even at low surface density of total gas of ~20 Msun pc^2. In most extreme case, NGC 5395 have a trend that fmol monotonically decreases as the surface density of total gas increases. To investigate the origin of high fmol in the interacting galaxies, we performed theoretical model fitting varying metallicity and external pressure. According to the model fitting, external pressure can explain high fmol in the interacting galaxies. We conclude that high external pressure which is occurred by the shock prevailing over whole galaxies even in the early stage of the interaction.
    Preview · Article · Nov 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We stacked 12CO and 13CO spectra of NGC3627 after redefining the velocity axis of each spectrum of the mapping data so that the zero corresponds to the local mean velocity of the 12CO spectra. The signal-to-noise ratios of the resulting spectra are improved by a factor of up to 3.2 compared to those obtained with normal stacking analysis. We successfully detect a weak 13CO emission from the interarm region where the emission was not detected in the individual pointings. We compare the integrated intensity ratios I12CO/I13CO among six characteristic regions (center, bar, bar-end, offset, arm, and interarm). We find that I12CO/I13CO in the bar and interarm are higher than those in the other regions by a factor of ∼2 and I12CO/I13CO in the center ismoderately high. These high I12CO/I13CO ratios in the bar and center are attributed to a high intensity ratio (T12CO/T13CO), and that in the interarm is attributed to a high ratio of the full width at half maximum of spectra (FWHM12CO/FWHM13CO). The difference between FWHM12CO and FWHM13CO of the interarm indicates the existence of two components, one with a narrow line width (∼ FWHM13CO) and the other with a broad line width (∼ FWHM12CO). Additionally, the T12CO/T13CO ratio in the broad-line-width component of the interarm is higher than the other regions. The high T12CO/T13CO in the center and bar and of the broad-line-width component in the interarm suggest the existence of non-optically thick 12CO components. We find that more than half of the 12CO emissions of the interarm are likely to be radiated from the diffuse component. Our result suggests that the use of a universal CO-to-H2 conversion factor might lead to an overestimation of molecular gas mass and underestimation of star-formation efficiency in the interarm by a factor of a few.
    Preview · Article · Sep 2014 · Publications- Astronomical Society of Japan
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the development of the software-based polarization spectrometer‘ PolariS ’and early results from commissioning on the Nobeyama 45-m radio telescope. PolariS aims to detect the Zeeman effect of CCS line to measure ~ 100 μG magnetic fields in star-forming molecular cores. The PolariS consists of the K5/VSSP32 digitizer and a Linux-based PC with a GPU to process full-Stokes spectroscopy of 2 x 131072 ch for bandwidth of 4 or 8 MHz. We have verified performance of PolariS and succeeded to take full-stokes spectra of SiO masers. Since the code is open at GitHub everybody can utilize it.
    No preview · Conference Paper · Jul 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: We compared theoretical and observational molecular mass fractions (fmol: ratio of molecular gas density to total gas density) using observational data of ten nearby spiral galaxies. For determination of fmol, the three parameters–interstellar pressure P, UV radiation U, and metallicity Z–were obtained from the spectral line data of 12CO(J = 1–0), H i, Hα, [O iii], and [O ii]. Interstellar pressure was calculated with the sum of the hydrogen gas densities and the stellar potential based on the Ks-band data. For most data other than metallicity, we used archived NRO CO Atlas, THINGS, SINGS, and 2MASS data. For comparison, we also investigated the dependence of the CO-to-H2 conversion factor XCO. It was found that the theoretical fmol agreed with the observational fmol only when the interstellar pressure is calculated with both the gas density and stellar disk potential. To fit observations more accurately, either the metallicity or the UV radiation needs to be adjusted. It was also found that, in UV radiation scaling, scaling factor γ has a correlation with the diffuse fraction of the Hα emission line data, fDIG. As for XCO, it was shown that the difference between both values of fmol becomes the least when XCO is 1.0 × 1020 cm−2 (K km s−1)−1.
    No preview · Article · Jul 2014 · Publications- Astronomical Society of Japan
  • Source
    [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.
    Preview · Article · Jul 2014 · The Astrophysical Journal Letters
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jun 2014 · The Astrophysical Journal
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · May 2014
  • Source
    [Show abstract] [Hide abstract]
    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.
    Preview · Article · Apr 2014 · Publications- Astronomical Society of Japan
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Apr 2014
  • Source
    G. Natale · K. Foyle · C. D. Wilson · N. Kuno
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a multiwavelength study of a sample of far-infrared (FIR) sources detected on the Herschel broad--band maps of the nearby galaxy M33. We perform source photometry on the FIR maps as well as mid-infrared (MIR), H$\alpha$, far-ultraviolet and integrated HI and CO line emission maps. By fitting MIR/FIR dust emission spectra, the source dust masses, temperatures and luminosities are inferred. The sources are classified based on their H$\alpha$ morphology (substructured versus not-substructured) and on whether they have a significant CO detection ($S/N>$3$\sigma$). We find that the sources have dust masses in the range 10$^2$-10$^4$~M$_\odot$ and that they present significant differences in their inferred dust/star formation/gas parameters depending on their H$\alpha$ morphology and CO detection classification. The results suggests differences in the evolutionary states or in the number of embedded HII regions between the subsamples. The source background--subtracted dust emission seems to be predominantly powered by local star formation, as indicated by a strong correlation between the dust luminosity and the dust-corrected H$\alpha$ luminosity and the fact that the extrapolated young stellar luminosity is high enough to account for the observed dust emission. Finally, we do not find a strong correlation between the dust-corrected H$\alpha$ luminosity and the dust mass of the sources, consistent with previous results on the breakdown of simple scaling relations at sub-kpc scales. However, the scatter in the relation is significantly reduced by correcting the H$\alpha$ luminosity for the age of the young stellar populations in the star--forming regions.
    Preview · Article · Apr 2014 · Monthly Notices of the Royal Astronomical Society
  • Y. Miyamoto · N. Nakai · N. Kuno
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Feb 2014
  • Source
    Yusuke Miyamoto · Naomasa Nakai · Nario Kuno
    [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the dynamics of the molecular gas and the evolution of giant molecular associations (GMAs) in the spiral galaxy M 51 with the Nobeyama Radio Observatory 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 giant molecular clouds (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 factors indicate that the shear motion is an important factor in evolution of GMCs and GMAs.
    Preview · Article · Nov 2013 · Publications- Astronomical Society of Japan
  • Source
    Hsi-An Pan · Nario Kuno · Akihiko Hirota
    [Show abstract] [Hide abstract]
    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 ($\Sigma_{\mathrm{H_{2}}}$) derived from 12CO and 13CO are consistent with the environment in a high-$\Sigma _{\mathrm{H_{2}}}$ 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 the K–S law (N) increases toward the central region. Furthermore, the dependence of N on $\Sigma _{\mathrm{H_{2}}}$ is observed. Specifically, N increases with $\Sigma _{\mathrm{H_{2}}}$. 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-$\Sigma _{\mathrm{H_{2}}}$ region) of IC 342 and both gravitational instability and cloud–cloud collisions in the central region (high-$\Sigma _{\mathrm{H_{2}}}$ regime). In addition, the increasing N toward the high-$\Sigma _{\mathrm{H_{2}}}$ 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.
    Preview · Article · Nov 2013 · Publications- Astronomical Society of Japan

Publication Stats

1k Citations
290.29 Total Impact Points

Institutions

  • 2014-2015
    • University of Tsukuba
      Tsukuba, Ibaraki, Japan
    • Osaka Prefecture University
      • Department of Physical Science
      Sakai, Ōsaka, Japan
  • 2009-2014
    • The Graduate University for Advanced Studies
      • Department of Astronomical Science
      Миура, Kanagawa, Japan
  • 2002-2014
    • National Astronomical Observatory of Japan
      • Astronomy Data Center
      Edo, Tōkyō, Japan
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2013
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 2012
    • Joetsu University of Education
      Niahi-niigata, Niigata, Japan
  • 2010
    • National Institutes Of Natural Sciences
      Edo, Tokyo, Japan
  • 1995-2010
    • The University of Tokyo
      • Department of Astronomy
      Tokyo, Tokyo-to, Japan
  • 2002-2008
    • Hokkaido University
      • Division of Physics
      Sapporo, Hokkaidō, Japan
  • 2007
    • Tohoku University
      • Astronomical Institute
      Japan
  • 2003
    • University of Cambridge
      Cambridge, England, United Kingdom
  • 2001
    • The University of Arizona
      Tucson, Arizona, United States
  • 1999
    • Kyoto University
      Kioto, Kyoto, Japan