Publishing type：Research paper (scientific journal)  

DOI： 10.1093/mnras/stad2715

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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We present position–position–velocity (PPV) cubes of the physical and chemical properties of the molecular medium in the central 1.2 kpc region of the active galaxy NGC 613 at a PPV resolution of 0.″8 × 0.″8 × 10 km s⁻¹ (0.″8 = ∼68 pc). We used eight molecular lines (¹³CO(1–0), C¹⁸O(1–0), HCN(1–0), HCO⁺(1–0), CS(2–1), HCN(4–3), HCO⁺(4–3), and CS(7–6)) obtained with the Atacama Large Millimeter/submillimeter Array. Non-LTE calculation with hierarchical Bayesian inference was used to construct PPV cubes of the gas kinetic temperature (T_kin), molecular hydrogen volume density (${n}_{ { {\rm{H } } }_{2 } }$), column densities (${N}_{ { {\rm{H } } }_{2 } }$), and fractional abundances of four molecules (¹²C¹⁸O, HCN, HCO⁺, and CS). The derived ${n}_{ { {\rm{H } } }_{2 } }$, ${N}_{ { {\rm{H } } }_{2 } }$, and T_kin ranged from 10^3.21−3.85 cm⁻³, 10^20.8−22.1 cm⁻², and 10^2.33−2.64 K, respectively. Our first application of the non-LTE method with the hierarchical Bayesian inference to external galaxies yielded compatible results compared with the previous studies of this galaxy, demonstrating the efficacy of this method for application to other galaxies. We examined the correlation between gas surface density ${ { \rm{\Sigma } } }_{ { {\rm{H } } }_{2 } }$ (converted from ${N}_{ { {\rm{H } } }_{2 } }$) and the star formation rate Σ_SFR obtained from the 110 GHz continuum flux map and found two distinct sequences in the ${ { \rm{\Sigma } } }_{ { {\rm{H } } }_{2 } }$–Σ_SFR diagram; the southwestern subregion of the star-forming ring exhibited a ∼0.5 dex higher star formation efficiency (SFE; Σ_SFR/${ { \rm{\Sigma } } }_{ { {\rm{H } } }_{2 } }$) than the eastern subregion. However, they exhibited no systematic difference in ${n}_{ { {\rm{H } } }_{2 } }$, which is often argued as a driver of SFE variation. We suggest that the deficiency of molecular gas in the southwestern subregion, where no significant gas supply is evident along the offset ridges in the bar, is responsible for the elevated SFE.

DOI： 10.3847/1538-4357/ace260

arXiv

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ace260/pdf

Publishing type：Research paper (scientific journal)  

We simultaneously measured the spatially-resolved CO-to-H$_{2}$ conversion
factor ($\alpha_\mathrm{CO}$) and dust-to-gas ratio (DGR) in nearby galaxies on
a kiloparsec scale. In this study, we used $^{12}$CO($J=1-0$) data obtained by
the Nobeyama 45-m radio telescope with HI and dust mass surface densities. We
obtained the values of global $\alpha_\mathrm{CO}$ and DGR in 22 nearby spiral
galaxies, with averages of $2.66 \pm 1.36\ M_\odot\ \mathrm{pc}^{-2}\
(\mathrm{K\ km\ s^{-1 } })^{-1}$ and $0.0052 \pm 0.0026$, respectively.
Furthermore, the radial variations of $\alpha_\mathrm{CO}$ and DGR in four
barred spiral galaxies (IC 342, NGC 3627, NGC 5236, and NGC 6946) were obtained
by dividing them into the inner and outer regions with a boundary of
$0.2R_{25}$, where $R_{25}$ is the isophotal radius at 25 mag arcsec$^{-2}$ in
the $B$ band. The averages of $\alpha_\mathrm{CO}$ and DGR in the inner region
($\leq 0.2R_{25}$) are $0.36 \pm 0.08\ M_\odot\ \mathrm{pc}^{-2}\ (\mathrm{K\
km\ s^{-1 } })^{-1}$ and $0.0199 \pm 0.0058$, while those in the outer region ($>
0.2R_{25}$) are $1.49 \pm 0.76\ M_\odot\ \mathrm{pc}^{-2}\ (\mathrm{K\ km\
s^{-1 } })^{-1}$ and $0.0084 \pm 0.0037$, respectively. The value of
$\alpha_\mathrm{CO}$ in the outer region is 2.3 to 5.3 times larger than that
of the inner region. When separated into the inner and outer regions, we find
that $\alpha_\mathrm{CO}$ and DGR correlate with the metallicity and the star
formation rate surface density. The value of $\alpha_\mathrm{CO}$ derived in
this study tends to be smaller than those obtained in previous studies for the
Milky Way and nearby star-forming galaxies. This fact can be attributed to our
measurements being biased toward the inner region; we measured
$\alpha_\mathrm{CO}$ at 0.85 and 0.76 times smaller in radius than the previous
works for nearby star-forming galaxies and the Milky Way, respectively.

DOI： 10.1093/pasj/psad034

arXiv

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Other Link： http://arxiv.org/pdf/2305.07827v1

Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

We have performed CO J = 1–0 observations of 10 galaxies hosting luminous (Lbol > 1046 erg s−1) type 1 active galactic nuclei (AGNs) with the Nobeyama 45 m radio telescope. The targets are selected because they are expected to be rich in molecular gas based on their high nebular dust extinction (AV). However, no significant CO emission lines were detected in any of the targets. The upper limits of the CO J = 1–0 luminosities are lower than expected given the molecular gas mass inferred from the nebular AV. This inconsistency may be due to overestimated AV values due to the lack of stellar absorption correction. Considering more reliable AV values, the CO J = 1–0 non-detections by Nobeyama 45 m are natural. This suggests that our results do not contradict the conversion methods from AV to molecular gas mass proposed in the literature. This survey suggests that careful AV measurements as well as CO observations are still needed to improve the measurements or estimates of the molecular gas content of galaxies hosting luminous AGNs.

DOI： 10.1093/pasj/psad039

arXiv

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/pasj/psad025

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

ABSTRACT

Radio-loud active galactic nuclei (RLAGNs) are rare among AGN populations. Lacking high-resolution and high-frequency observations, their structure and evolution stages are not well understood at high redshifts. In this work, we report Atacama Large Millimeter/submillimeter Array 237 GHz continuum observation at 0.023 arcsec resolution and Very Large Array (VLA) 44 GHz continuum observation at 0.08 arcsec resolution of the radio continuum emission from a high-redshift radio and hyper-luminous infrared galaxy at z = 1.92. The new observations confirm the South-East (SE) and North-West (NW) hotspots identified by previous low-resolution VLA observations at 4.7 and 8.2 GHz and identify a radio core undetected in all previous observations. The SE hotspot has a higher flux density than the NW one does by a factor of 6, suggesting that there can be a Doppler boosting effect in the SE one. In this scenario, we estimate the advance speed of the jet head, ranging from ∼0.1c to 0.3c, which yields a mildly relativistic case. The projected linear distance between the two hotspots is ∼13 kpc, yielding a linear size (≤20 kpc) of a compact-steep-spectrum (CSS) source. Combined with new high-frequency (νobs ≥ 44 GHz) and archived low-frequency observations (νobs ≤ 8.2 GHz), we find that injection spectra of both NW and SE hotspots can be fitted with a continuous injection (CI) model. Based on the CI model, the synchrotron ages of NW and SE hotspots have an order of 105 yr, consistent with the order of magnitude 103–105 yr observed in CSS sources associated with radio AGNs at an early evolution stage. The CI model also favours the scenario in which the double hotspots have experienced a quiescent phase, suggesting that this RLAGN may have transient or intermittent activities.

DOI： 10.1093/mnras/stad1428

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Other Link： https://academic.oup.com/mnras/article-pdf/522/4/6123/50420114/stad1428.pdf

Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Simultaneous multi-band very long baseline interferometry (VLBI) observations at millimeter wavelengths have huge potential for various science cases. However, there exist difficulties in expanding the scientific targets, as the sensitivity of radio telescopes at millimeter wavelengths is typically lower compared to that at centimeter wavelengths. In order to realize high-sensitivity mm-VLBI observations in the East Asia region, we are promoting the HINOTORI (Hybrid Installation project in NObeyama, Triple-band ORIented) project, which aims to launch the wide-band and simultaneous triple-band (22/43/86 GHz) VLBI system with the Nobeyama 45 m Radio Telescope (NRO45). The simultaneous 22/43 GHz observation mode has already been operated for the open-use program. We have recently completed the performance evaluation of the receiver and observing system at 86 GHz. In addition, a new wide-band VLBI back-end system has been installed on the NRO45 and the performance of this receiving system has been found to be sufficient to meet scientific requirements. Currently, we are performing commissioning observations to establish regular VLBI operation with simultaneous triple-band mode together with the Korean VLBI Network. The participation of the NRO45 is expected to strengthen the mm-VLBI observation network in the East Asia region and to be a very powerful addition with respect to the science of of black hole jets.

DOI： 10.3390/galaxies11010030

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press ({OUP})  

Machine learning has been successfully applied in varied field but whether it
is a viable tool for determining the distance to molecular clouds in the Galaxy
is an open question. In the Galaxy, the kinematic distance is commonly employed
as the distance to a molecular cloud. However, there is a problem in that for
the inner Galaxy, two different solutions, the ``Near'' solution, and the
``Far'' solution, can be derived simultaneously. We attempted to construct a
two-class (``Near'' or ``Far'') inference model using a Convolutional Neural
Network (CNN), a form of deep learning that can capture spatial features
generally. In this study, we used the CO dataset toward the 1st quadrant of the
Galactic plane obtained with the Nobeyama 45-m radio telescope (l = 62-10
degree, |b| < 1 degree). In the model, we applied the three-dimensional
distribution (position-position-velocity) of the 12CO (J=1-0) emissions as the
main input. The dataset with ``Near'' or ``Far'' annotation was made from the
HII region catalog of the infrared astronomy satellite WISE to train the model.
As a result, we could construct a CNN model with a 76% accuracy rate on the
training dataset. By using the model, we determined the distance to molecular
clouds identified by the CLUMPFIND algorithm. We found that the mass of the
molecular clouds with a distance of < 8.15 kpc identified in the 12CO data
follows a power-law distribution with an index of about -2.3 in the mass range
of M >10^3 Msun. Also, the detailed molecular gas distribution of the Galaxy as
seen from the Galactic North pole was determined.

DOI： 10.1093/pasj/psac104

arXiv

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Other Link： http://arxiv.org/pdf/2212.06238v1

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2628664

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

We study properties of the interstellar medium, an ingredient of stars, and star formation activity, in four nearby galaxy pairs in the early and mid stages of interaction for both a galaxy scale and a kpc scale. The galaxy-scale Kennicutt–Schmidt law shows that seven of eight interacting galaxies have a star formation rate within a factor of three compared with the best fit of the isolated galaxies, although we have shown that molecular hydrogen gas is efficiently produced from atomic hydrogen during the interaction in the previous paper (Kaneko et al. 2017 PASJ, 69, 66). The galaxy-scale specific star formation rate (sSFR) and star formation efficiency (SFE) in interacting galaxies are comparable to those in isolated galaxies. We also investigate SFE and the Kennicutt–Schmidt law on a kpc scale. The spatial distributions of SFE reveal that SFE is locally enhanced, and the enhanced regions take place asymmetrically or at off-centre regions. The local enhancement of SFE could be induced by shock. We find that the index of the Kennicutt–Schmidt law for the interacting galaxies in the early stage is 1.30 ± 0.04, which is consistent with that of the isolated galaxies. Since CO emission, which is used in the Kennicutt–Schmidt law, is a tracer of the amount of molecular gas, this fact suggests that dense gas, which is more directly connected to star formation, is not changed at the early stage of interaction.

DOI： 10.1093/pasj/psab129

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We present Atacama Large Millimeter/submillimeter Array observations of multiple ¹²CO, ¹³CO, and C¹⁸O lines and 2.9 mm and 1.3 mm continuum emission toward the nearby interacting luminous infrared galaxy NGC 3110, supplemented with similar spatial resolution Hα, 1.4 GHz continuum, and K-band data. We estimate the typical CO-to-H₂ conversion factor of 1.7 M_⊙ (K km s⁻¹ pc²)⁻¹ within the disk using local thermal equilibrium-based and dust-based H₂ column densities, and measure the 1 kpc scale surface densities of the star formation rate (Σ_SFR), super star clusters (Σ_SSC), molecular gas mass, and star formation efficiency (SFE) toward the entire gas disk. These parameters show a peak in the southern part of the southern spiral arm (SFE ∼ 10^−8.2 yr⁻¹, Σ_SFR ∼ 10^−0.6M_⊙ kpc⁻² yr⁻¹, Σ_SSC ∼ 6.0 kpc⁻²), which is likely attributable to the ongoing tidal interaction with the companion galaxy MCG-01-26-013, as well as toward the circumnuclear region. We also find that thermal free–free emission contributes to a significant fraction of the millimeter continuum emission at the position of the southern peak. These measurements imply that the peak of the southern arm is an active and young star-forming region, whereas the central part of NGC 3110 is a site of long-continued star formation. We suggest that during the early stage of the galaxy–galaxy interaction in which the mass ratio was high in NGC 3110, fragmentation along the main galaxy arms is an important driver of merger-induced star formation, and that massive gas inflow results in dusty nuclear starbursts.

DOI： 10.3847/1538-4357/ac5f41

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ac5f41/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
While molecular gas mass is usually derived from 12CO(J = 1–0)—the most fundamental line for exploring molecular gas—it is often derived from 12CO(J = 2–1) assuming a constant 12CO(J = 2–1)$/$12CO(J = 1–0) line ratio (R2/1). We present variations of R2/1 and effects of the assumption that R2/1 is a constant in 24 nearby galaxies using 12CO data obtained with the Nobeyama 45 m radio telescope and IRAM 30 m telescope. The median of R2/1 for all galaxies is 0.61, and the weighted mean of R2/1 by 12CO(J = 1–0) integrated intensity is 0.66 with a standard deviation of 0.19. The radial variation of R2/1 shows that it is high (∼0.8) in the inner ∼1 kpc while its median in disks is nearly constant at 0.60 when all galaxies are compiled. In the case that the constant R2/1 of 0.7 is adopted, we found that the total molecular gas mass derived from 12CO(J = 2–1) is underestimated/overestimated by ∼20%, and at most by 35%. The scatter of molecular gas surface density within each galaxy becomes larger by ∼30%, and at most by 120%. Indices of the spatially resolved Kennicutt–Schmidt relation by 12CO(J = 2–1) are underestimated by 10%–20%, at most 39%, in 17 out of 24 galaxies. R2/1 has good positive correlations with star-formation rate and infrared color, and a negative correlation with molecular gas depletion time. There is a clear tendency of increasing R2/1 with increasing kinetic temperature (Tkin). Further, we found that not only Tkin but also pressure of molecular gas is important in understanding variations of R2/1. Special considerations should be made when discussing molecular gas mass and molecular gas properties inferred from 12CO(J = 2–1) instead of 12CO(J = 1–0).

DOI： 10.1093/pasj/psaa119

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

We present observations of the 3P1–3P0 fine-structure line of atomic carbon using the ASTE 10m sub-mm telescope towards RCW 38, the youngest super star cluster in the Milky Way. The detected [C i] emission is compared with the CO J = 1–0 image cube presented in Fukui et al. (2016, ApJ, 820, 26) which has an angular resolution of 40″ (∼0.33 pc). The overall distribution of the [C i] emission in this cluster is similar to that of the 13CO emission. The optical depth of the [C i] emission was found to be τ = 0.1–0.6, suggesting mostly optically thin emission. An empirical conversion factor from the [C i] integrated intensity to the H2 column density was estimated as X[C i]$= 6.3 \times 10 ^{20}\:$cm−2 K−1 km−1 s (for visual extinction: AV ≤ 10 mag) and 1.4 × 1021 cm−2 K−1 km−1 s (for AV of 10–100 mag). The column density ratio of the [C i] to CO (N[C i]$/N_{\rm CO}$) was derived as ∼0.1 for AV of 10–100 mag, which is consistent with that of the Orion cloud presented in Ikeda et al. (2002, ApJ, 571, 560). However, our results cover an AV regime of up to 100 mag, which is wider than the coverage found in Orion, which reaches up to ∼60 mag. Such a high [C i]$/$CO ratio in a high-AV region is difficult to explain via the plane-parallel photodissociation region model, which predicts that this ratio is close to 0 due to the heavy shielding of the ultraviolet (UV) radiation. Our results suggest that the molecular gas in this cluster is highly clumpy, allowing deep penetration of UV radiation even at averaged AV values of 100 mag. Recent theoretical works have presented models consistent with such clumped gas distribution with a sub-pc clump size (e.g., Tachihara et al. 2018, arXiv:1811.02224).

DOI： 10.1093/pasj/psaa113

arXiv

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2560830

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2562137

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

Aims. We construct the molecular mass function using the bivariate K-band-mass function (BMF) of the Herschel Reference Survey (HRS), which is a volume-limited sample that has already been widely studied at the entire electromagnetic spectrum.

Methods. The molecular mass function was derived from the K-band and the gas mass cumulative distribution using a copula method, which is described in detail in our previous papers.

Results. The H₂ mass is relatively strongly correlated with the K-band luminosity because of the tight relation between the stellar mass and the molecular gas mass within the sample with a scatter, which is likely due to those galaxies which have lost their molecular content because of environmental effects or because of a larger gas consumption due to past star formation processes. The derived H₂ MF samples the molecular mass range from ∼4 × 10⁶M_⊙ to ∼10¹⁰ M_⊙, and when compared with theoretical models, it agrees well with the theoretical predictions at the lower end of the mass values; whereas at masses larger than 10¹⁰ M_⊙, the HRS sample may miss galaxies with a large content of molecular hydrogen and the outcomes are not conclusive. The value of the local density of the molecular gas mass inferred from our analysis is ∼1.5 × 10⁷ M_⊙ Mpc⁻³, and it is compared with the results at larger redshifts, confirming the lack of strong evolution for the molecular mass density between z = 0 and z = 4.

Conclusions. This is the first molecular mass function that has been derived on a complete sample in the local Universe, which can be used as a reliable calibration at redshift z = 0 for models aiming to predict the evolution of the molecular mass density.

DOI： 10.1051/0004-6361/202038675

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
We investigate the molecular gas properties of galaxies across the main sequence of star-forming (SF) galaxies in the local Universe using 12CO(J = 1–0), hereafter 12CO, and 13CO(J = 1–0), hereafter 13CO, mapping data of 147 nearby galaxies obtained in the COMING project, a legacy project of the Nobeyama Radio Observatory. In order to improve the signal-to-noise ratios of both lines, we stack all the pixels where 12CO emission is detected after aligning the line center expected from the first-moment map of 12CO. As a result, 13CO emission is successfully detected in 80 galaxies with a signal-to-noise ratio larger than three. The error-weighted mean of the integrated-intensity ratio of 12CO to 13CO lines (R1213) of the 80 galaxies is 10.9, with a standard deviation of 7.0. We find that (1) R1213 positively correlates to specific star-formation rate (sSFR) with a correlation coefficient of 0.46, and (2) both the flux ratio of IRAS 60 μm to 100 μm (f60/f100) and the inclination-corrected linewidth of 12CO stacked spectra ($\sigma _{ { \rm ^{12}CO},i}$) also correlate with sSFR for galaxies with the R1213 measurement. Our results support the scenario where R1213 variation is mainly caused by changes in molecular gas properties such as temperature and turbulence. The consequent variation of the CO-to-H2 conversion factor across the SF main sequence is not large enough to completely extinguish the known correlations between sSFR and Mmol/Mstar (μmol) or star-formation efficiency (SFE) reported in previous studies, while this variation would strengthen (weaken) the sSFR–SFE (sSFR–μmol) correlation.

DOI： 10.1093/pasj/psaa084

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Publishing type：Research paper (scientific journal)  

We present the results of ^{12}CO(J = 1-0) and ^{13}CO(J = 1-0) simultaneous mappings toward the nearby barred spiral galaxy NGC 4303 as part of the CO Multi-line Imaging of Nearby Galaxies (COMING) project. Barred spiral galaxies often show lower star-formation efficiency (SFE) in their bar region compared to the spiral arms. In this paper, we examine the relation between the SFEs and the volume densities of molecular gas n(H<SUB>2</SUB>) in the eight different regions within the galactic disk with CO data combined with archival far-ultraviolet and 24 μm data. We confirmed that SFE in the bar region is lower by 39% than that in the spiral arms. Moreover, velocity-alignment stacking analysis was performed for the spectra in the individual regions. Integrated intensity ratios of ^{12}CO to ^{13}CO (R<SUB>12/13</SUB>) ranging from 10 to 17 were the results of this stacking. Fixing a kinetic temperature of molecular gas, n({H_2}) was derived from R<SUB>12/13</SUB> via non-local thermodynamic equilibrium (non-LTE) analysis. The density n(H<SUB>2</SUB>) in the bar is lower by 31%-37% than that in the arms and there is a rather tight positive correlation between SFEs and n(H<SUB>2</SUB>), with a correlation coefficient of ̃0.8. Furthermore, we found a dependence of n({H}_2) on the velocity dispersion of inter-molecular clouds (∆V/sin i). Specifically, n(H<SUB>2</SUB>) increases as ∆V/sin i increases when ∆V/sin i &lt; 100 km s<SUP>-1</SUP>. On the other hand, n(H<SUB>2</SUB>) decreases as ∆V/sin i increases when ∆V/sin i &gt; 100 km s<SUP>-1</SUP>. These relations indicate that the variations of SFE could be caused by the volume densities of molecular gas, and the volume densities could be governed by the dynamical influence such as cloud-cloud collisions, shear, and enhanced inner-cloud turbulence....

DOI： 10.1093/pasj/psz022

arXiv

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Language：English   Publishing type：Research paper (scientific journal)  

Observations of the molecular gas in galaxies are vital to understand the evolution and star-forming histories of galaxies. However, galaxies with molecular gas maps of their whole discs at sufficient resolution to distinguish galactic structures are severely lacking. Millimeter-wavelength studies at a high angular resolution across multiple lines and transitions are particularly needed, severely limiting our ability to infer the universal properties of molecular gas in galaxies. Hence, we conducted a legacy project with the 45 m telescope of the Nobeyama Radio Observatory, called the CO Multi-line Imaging of Nearby Galaxies (COMING), which simultaneously observed 147 galaxies with high far-infrared (FIR) flux in <SUP>12</SUP>CO, <SUP>13</SUP>CO, and C<SUP>18</SUP>O J = 1-0 lines. The total molecular gas mass was derived using the standard CO-to-H<SUB>2</SUB> conversion factor and found to be positively correlated with the total stellar mass derived from the WISE 3.4 μm band data. The fraction of the total molecular gas mass to the total stellar mass in galaxies does not depend on their Hubble types nor the existence of a galactic bar, although when galaxies in individual morphological types are investigated separately, the fraction seems to decrease with the total stellar mass in early-type galaxies and vice versa in late-type galaxies. No differences in the distribution of the total molecular gas mass, stellar mass, or the total molecular gas to stellar mass ratio was observed between barred and non-barred galaxies, which is likely the result of our sample selection criteria, in that we prioritized observing FIR bright (and thus molecular gas-rich) galaxies....

DOI： 10.1093/pasj/psz115

arXiv

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Language：English   Publishing type：Research paper (scientific journal)  

We examined radial variations in molecular-gas based star formation efficiency (SFE), which is defined as star formation rate per unit molecular gas mass, for 80 galaxies selected from the CO Multi-line Imaging of Nearby Galaxies project (Sorai et al. 2019, PASJ, 71, S14). The radial variations in SFE for individual galaxies are typically a factor of 2-3, which suggests that SFE is nearly constant along the galactocentric radius. We found an averaged SFE in 80 galaxies of (1.69 ± 1.1) × 10<SUP>-9</SUP> yr<SUP>-1</SUP>, which is consistent with Leroy et al. (2008, AJ, 136, 2782) if we consider the contribution of helium to the molecular gas mass evaluation and the difference in the assumed initial mass function between the two studies. We compared SFE among different morphological (i.e., SA, SAB, and SB) types, and found that SFE within the inner radii (r/r<SUB>25</SUB> &lt; 0.3, where r<SUB>25</SUB> is the B-band isophotal radius at 25 mag arcsec<SUP>-2</SUP>) of SB galaxies is slightly higher than that of SA and SAB galaxies. This trend can be partly explained by the dependence of SFE on global stellar mass, which probably relates to the CO-to-H<SUB>2</SUB> conversion factor through the metallicity. For two representative SB galaxies in our sample, NGC 3367 and NGC 7479, the ellipse of r/r<SUB>25</SUB> = 0.3 seems to cover not only the central region but also the inner part of the disk, mainly the bar. These two galaxies show higher SFE in the bar than in the spiral arms. However, we found an opposite trend in NGC 4303; SFE is lower in the bar than in the spiral arms, which is consistent with earlier studies (e.g., Momose et al. 2010, ApJ, 721, 383). These results suggest a diversity of star formation activities in the bar....

DOI： 10.1093/pasj/psz015

arXiv

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Language：English   Publishing type：Research paper (scientific journal)  

We present the results of ^{12}CO(J = 1-0) and ^{13}CO(J = 1-0) simultaneous mappings toward the nearby barred spiral galaxy NGC 4303 as part of the CO Multi-line Imaging of Nearby Galaxies (COMING) project. Barred spiral galaxies often show lower star-formation efficiency (SFE) in their bar region compared to the spiral arms. In this paper, we examine the relation between the SFEs and the volume densities of molecular gas n(H<SUB>2</SUB>) in the eight different regions within the galactic disk with CO data combined with archival far-ultraviolet and 24 μm data. We confirmed that SFE in the bar region is lower by 39% than that in the spiral arms. Moreover, velocity-alignment stacking analysis was performed for the spectra in the individual regions. Integrated intensity ratios of ^{12}CO to ^{13}CO (R<SUB>12/13</SUB>) ranging from 10 to 17 were the results of this stacking. Fixing a kinetic temperature of molecular gas, n({H_2}) was derived from R<SUB>12/13</SUB> via non-local thermodynamic equilibrium (non-LTE) analysis. The density n(H<SUB>2</SUB>) in the bar is lower by 31%-37% than that in the arms and there is a rather tight positive correlation between SFEs and n(H<SUB>2</SUB>), with a correlation coefficient of ̃0.8. Furthermore, we found a dependence of n({H}_2) on the velocity dispersion of inter-molecular clouds (∆V/sin i). Specifically, n(H<SUB>2</SUB>) increases as ∆V/sin i increases when ∆V/sin i &lt; 100 km s<SUP>-1</SUP>. On the other hand, n(H<SUB>2</SUB>) decreases as ∆V/sin i increases when ∆V/sin i &gt; 100 km s<SUP>-1</SUP>. These relations indicate that the variations of SFE could be caused by the volume densities of molecular gas, and the volume densities could be governed by the dynamical influence such as cloud-cloud collisions, shear, and enhanced inner-cloud turbulence....

DOI： 10.1093/pasj/psz022

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

We present the results of ^{12}CO(J = 1-0) and ^{13}CO(J = 1-0) simultaneous mappings toward the nearby barred spiral galaxy NGC 4303 as part of the CO Multi-line Imaging of Nearby Galaxies (COMING) project. Barred spiral galaxies often show lower star-formation efficiency (SFE) in their bar region compared to the spiral arms. In this paper, we examine the relation between the SFEs and the volume densities of molecular gas n(H&lt;SUB&gt;2&lt;/SUB&gt;) in the eight different regions within the galactic disk with CO data combined with archival far-ultraviolet and 24 μm data. We confirmed that SFE in the bar region is lower by 39% than that in the spiral arms. Moreover, velocity-alignment stacking analysis was performed for the spectra in the individual regions. Integrated intensity ratios of ^{12}CO to ^{13}CO (R&lt;SUB&gt;12/13&lt;/SUB&gt;) ranging from 10 to 17 were the results of this stacking. Fixing a kinetic temperature of molecular gas, n({H_2}) was derived from R&lt;SUB&gt;12/13&lt;/SUB&gt; via non-local thermodynamic equilibrium (non-LTE) analysis. The density n(H&lt;SUB&gt;2&lt;/SUB&gt;) in the bar is lower by 31%-37% than that in the arms and there is a rather tight positive correlation between SFEs and n(H&lt;SUB&gt;2&lt;/SUB&gt;), with a correlation coefficient of ̃0.8. Furthermore, we found a dependence of n({H}_2) on the velocity dispersion of inter-molecular clouds (∆V/sin i). Specifically, n(H&lt;SUB&gt;2&lt;/SUB&gt;) increases as ∆V/sin i increases when ∆V/sin i &amp;lt; 100 km s&lt;SUP&gt;-1&lt;/SUP&gt;. On the other hand, n(H&lt;SUB&gt;2&lt;/SUB&gt;) decreases as ∆V/sin i increases when ∆V/sin i &amp;gt; 100 km s&lt;SUP&gt;-1&lt;/SUP&gt;. These relations indicate that the variations of SFE could be caused by the volume densities of molecular gas, and the volume densities could be governed by the dynamical influence such as cloud-cloud collisions, shear, and enhanced inner-cloud turbulence....

DOI： 10.1093/pasj/psz022

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

We examined radial variations in molecular-gas based star formation efficiency (SFE), which is defined as star formation rate per unit molecular gas mass, for 80 galaxies selected from the CO Multi-line Imaging of Nearby Galaxies project (Sorai et al. 2019, PASJ, submitted).The radial variations in SFE for individual galaxies are typically a factor of 2-3, which suggests that SFE is nearly constant along the galactocentric radius. We found an averaged SFE in 80 galaxies of (1.69 ± 1.1) × 10&lt;SUP&gt;-9&lt;/SUP&gt; yr&lt;SUP&gt;-1&lt;/SUP&gt;, which is consistent with Leroy et al. (2008, AJ, 136, 2782) if we consider the contribution of helium to the molecular gas mass evaluation and the difference in the assumed initial mass function between the two studies. We compared SFE among different morphological (i.e., SA, SAB, and SB) types, and found that SFE within the inner radii (r/r&lt;SUB&gt;25&lt;/SUB&gt; &amp;lt; 0.3, where r&lt;SUB&gt;25&lt;/SUB&gt; is the B-band isophotal radius at 25 mag arcsec&lt;SUP&gt;-2&lt;/SUP&gt;) of SB galaxies is slightly higher than that of SA and SAB galaxies. This trend can be partly explained by the dependence of SFE on global stellar mass, which probably relates to the CO-to-H&lt;SUB&gt;2&lt;/SUB&gt; conversion factor through the metallicity. For two representative SB galaxies in our sample, NGC 3367 and NGC 7479, the ellipse of r/r&lt;SUB&gt;25&lt;/SUB&gt; = 0.3 seems to cover not only the central region but also the inner part of the disk, mainly the bar. These two galaxies show higher SFE in the bar than in the spiral arms. However, we found an opposite trend in NGC 4303; SFE is lower in the bar than in the spiral arms, which is consistent with earlier studies (e.g., Momose et al. 2010, ApJ, 721, 383). These results suggest a diversity of star formation activities in the bar....

DOI： 10.1093/pasj/psz015

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

The 12CO (J = 1→0) velocity fields of a sample of 20 nearby spiral galaxies, selected from the CO Multi-line Imaging of Nearby Galaxies (COMING) legacy project of Nobeyama Radio Observatory, have been analyzed by Fourier decomposition to determine their basic kinematic properties, such as circular and noncircular velocities. On average, the investigated barred (SAB and SB) galaxies exhibit a ratio of noncircular to circular velocities of molecular gas larger by a factor of 1.5-2 than non-barred (SA) spiral galaxies at radii within the bar semimajor axis ab at 1 kpc resolution, with a maximum at a radius of R/ab ≈ 0.3. Residual velocity field images, created by subtracting model velocity fields from the data, reveal that this trend is caused by kpc-scale streaming motions of molecular gas in the bar region. Applying a new method based on radial velocity reversal, we estimated the corotation radius RCR and bar pattern speed ωb in seven SAB and SB systems. The ratio of the corotation to bar radius is found to be in a range of R≡ RCRab approx 0.8-1.6, suggesting that intermediate (SBb-SBc), luminous barred spiral galaxies host fast and slow rotator bars. Tentative negative correlations are found for ωb vs. ab and ωb vs. total stellar mass M∗, indicating that bars in massive disks are larger and rotate slower, possibly a consequence of angular momentum transfer. The kinematic properties of SAB and SB galaxies, derived from Fourier decomposition, are compared with recent numerical simulations that incorporate various rotation curve models and galaxy interactions.

DOI： 10.1093/pasj/psz004

Scopus

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

The &lt;SUP&gt;12&lt;/SUP&gt;CO (J = 1→0) velocity fields of a sample of 20 nearby spiral galaxies, selected from the CO Multi-line Imaging of Nearby Galaxies (COMING) legacy project of Nobeyama Radio Observatory, have been analyzed by Fourier decomposition to determine their basic kinematic properties, such as circular and noncircular velocities. On average, the investigated barred (SAB and SB) galaxies exhibit a ratio of noncircular to circular velocities of molecular gas larger by a factor of 1.5-2 than non-barred (SA) spiral galaxies at radii within the bar semimajor axis a&lt;SUB&gt;b&lt;/SUB&gt; at 1 kpc resolution, with a maximum at a radius of R/a&lt;SUB&gt;b&lt;/SUB&gt; ≈ 0.3. Residual velocity field images, created by subtracting model velocity fields from the data, reveal that this trend is caused by kpc-scale streaming motions of molecular gas in the bar region. Applying a new method based on radial velocity reversal, we estimated the corotation radius R&lt;SUB&gt;CR&lt;/SUB&gt; and bar pattern speed Ω&lt;SUB&gt;b&lt;/SUB&gt; in seven SAB and SB systems. The ratio of the corotation to bar radius is found to be in a range of R≡ R_CR/a_b ≈ 0.8-1.6, suggesting that intermediate (SBb-SBc), luminous barred spiral galaxies host fast and slow rotator bars. Tentative negative correlations are found for Ω&lt;SUB&gt;b&lt;/SUB&gt; vs. a&lt;SUB&gt;b&lt;/SUB&gt; and Ω&lt;SUB&gt;b&lt;/SUB&gt; vs. total stellar mass M&lt;SUB&gt;*&lt;/SUB&gt;, indicating that bars in massive disks are larger and rotate slower, possibly a consequence of angular momentum transfer. The kinematic properties of SAB and SB galaxies, derived from Fourier decomposition, are compared with recent numerical simulations that incorporate various rotation curve models and galaxy interactions....

DOI： 10.1093/pasj/psz004

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We have carried out observations in the 42-46 and 82-103 GHz bands with the Nobeyama 45 m radio telescope, and in the 338.2-339.2 and 348.45-349.45 GHz bands with the ASTE 10 m telescope, toward three high-mass star-forming regions containing massive young stellar objects (MYSOs), G12.89+0.49, G16.86-2.16, and G28.28-0.36. We have detected HC<SUB>3</SUB>N including its <SUP>13</SUP>C and D isotopologues, CH<SUB>3</SUB>OH, CH<SUB>3</SUB>CCH, and several complex organic molecules. Using our previous results for HC<SUB>5</SUB>N in these sources, we compare their N(HC<SUB>5</SUB>N)/N(CH<SUB>3</SUB>OH) ratios. The ratio in G28.28-0.36 is derived to be {0.091}<SUB>-0.039</SUB><SUP>+0.109</SUP>, which is higher than that in G12.89+0.49 by one order of magnitude, and higher than in G16.86-2.16 by a factor of ̃5. We investigate the relationship between the N(HC<SUB>5</SUB>N)/N(CH<SUB>3</SUB>OH) and the N(CH<SUB>3</SUB>CCH)/N(CH<SUB>3</SUB>OH) ratios. The relationships of the two column density ratios in G28.28-0.36 and G16.86-2.16 are similar to each other, while HC<SUB>5</SUB>N is less abundant compared to CH<SUB>3</SUB>CCH in G12.89+0.49. These results imply a chemical diversity in the lukewarm (T ̃ 20-30 K) envelope around MYSOs. In addition, several spectral lines from complex organic molecules, including very-high-excitation energy lines, have been detected toward G12.89+0.49, while the line density is significantly low in G28.28-0.36. These results suggest that organic-poor MYSOs are surrounded by a carbon-chain-rich lukewarm envelope (G28.28-0.36), while organic-rich MYSOs, namely hot cores, are surrounded by a CH<SUB>3</SUB>OH-rich lukewarm envelope (G12.89+0.49 and G16.86-2.16)....

DOI： 10.3847/1538-4357/aade97

Scopus

arXiv

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Other Link： http://stacks.iop.org/0004-637X/866/i=2/a=150?key=crossref.03744e08852133e5cbcc0652160910e5

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We present results of 12CO(J = 1-0) imaging observations of NGC 4567/4568, a galaxy pair in a close encounter, with the Atacama Large Millimeter/Submillimeter Array (ALMA). For the first time, we find clear evidence of a molecular collision front with a velocity dispersion that is 16.8 ± 1.4 km s-1 at the overlapping region, owing to high spatial and velocity resolution. By integrating over the velocity width that corresponds to the molecular collision front, we find a long filamentary structure with a size of 1800 pc × 350 pc at the collision front. This filamentary molecular structure spatially coincides with a dark lane seen in the R-band image. We find four molecular clouds in the filament, each with a radius of 30 pc and mass of 106 M o
the radii matching a typical value for giant molecular clouds (GMCs) and the masses corresponding to those between GMCs and giant molecular associations (GMAs). All four clouds are gravitationally bound. The molecular filamentary structure and its physical conditions are similar to the structure expected via numerical simulation. The filament could be a progenitor of super star clusters.

DOI： 10.3847/2041-8213/aac895

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

Dense molecular gas tracers in the central 1 kpc region of the superwind galaxy NGC 1808 have been imaged by ALMA at a resolution of 1″ (̃50 pc). Integrated intensities and line intensity ratios of HCN (1-0), H<SUP>13</SUP>CN (1-0), HCO<SUP>+</SUP> (1-0), H<SUP>13</SUP>CO<SUP>+</SUP> (1-0), HOC<SUP>+</SUP> (1-0), HCO<SUP>+</SUP> (4-3), CS (2-1), C<SUB>2</SUB>H (1-0), and previously detected CO (1-0) and CO (3-2) are presented. SiO (2-1) and HNCO (4-3) are detected toward the circumnuclear disk (CND), indicating the presence of shocked dense gas. There is evidence that an enhanced intensity ratio of HCN (1-0)/HCO<SUP>+</SUP> (1-0) reflects star formation activity, possibly in terms of shock heating and electron excitation in the CND and a star-forming ring at radius ̃300 pc. A non-local thermodynamic equilibrium analysis indicates that the molecular gas traced by HCN, H<SUP>13</SUP>CN, HCO<SUP>+</SUP>, and H<SUP>13</SUP>CO<SUP>+</SUP> in the CND is dense ({n}<SUB>{ { {H</SUB> } }<SUB>2</SUB>}̃ {10}<SUP>5</SUP> {cm } }<SUP>-3</SUP>) and warm (20 K ≲ T <SUB>k</SUB> ≲ 100 K). The calculations yield a low average gas density of {n}<SUB>{ { {H</SUB> } }<SUB>2</SUB>}̃ {10}<SUP>2</SUP>{--}{10}<SUP>3</SUP> {cm } }<SUP>-3</SUP> for a temperature of {T}<SUB>{ { k</SUB> } }≳ 30 { { K } } in the nuclear outflow. Dense gas tracers HCN (1-0), HCO<SUP>+</SUP> (1-0), CS (2-1), and C<SUB>2</SUB>H (1-0) are detected for the first time in the superwind of NGC 1808, confirming the presence of a velocity gradient in the outflow direction....

DOI： 10.3847/1538-4357/aab2ac

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/mnrasl/slx207

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

ALMA imaging of the cold molecular medium in the nearby starburst galaxy NGC 1808 is presented. The observations reveal the distribution of molecular gas, traced by (CO)-C-12 (1-0) and (CO)-C-12 (3-2), and continuum (93 and 350 GHz) across the central 1 kpc starburst region at a high resolution of similar to 1 ''. A molecular gas torus (radius similar to 30 pc) is discovered in the circumnuclear disk (CND; central 100 pc), with a high CO (3-2)/CO (1-0) ratio of similar to 1, surrounded by massive (10(6) -10(7) M circle dot) clouds with high star formation efficiency (SFE similar to 10(-8) yr(-1)), molecular spiral arms, and a 500 pc pseudo-ring. The CND harbors a continuum core and molecular gas exhibiting peculiar motion. The new data confirm the line splitting along the minor galactic axis, interpreted as a nuclear gas outflow with average velocity similar to 180 km s(-1), and show evidence of a velocity gradient of similar to+0.4 km s(-1) pc(-1) along the axis. In addition, supershells expanding from the 500 pc ring with maximum velocities of similar to 75 km s(-1) are revealed. The distribution and CO luminosities of molecular clouds in the central 1 kpc starburst region indicate an evolutionary sequence, from gas accretion onto the 500 pc ring from the large-scale bar to enhanced star formation in the ring, and outflow as feedback.

DOI： 10.3847/1538-4357/aa91cb

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report ALMA observations of molecular gas and continuum emission in the 90 and 350 GHz bands toward a nearby Seyfert galaxy, NGC 613. Radio continuum emissions were detected at 95 and 350 GHz from both the circumnuclear disk (CND) (r less than or similar to 90 pc) and a star-forming ring (250 less than or similar to r less than or similar to 340 pc), and the 95 GHz continuum was observed to extend from the center at a position angle of 20 degrees +/- 8 degrees. The archival 4.9 GHz data and our 95 GHz data show spectral indices of alpha less than or similar to -0.6 and -0.2 alongthe jets and in the star-forming ring; these can be produced by synchrotron emission and free-free emission, respectively. In addition, we detected the emission of CO(3-2), HCN(1-0), HCN(4-3), HCO+(1-0), HCO+(4-3), CS(2-1), and CS(7-6) in both the CND and the ring. The rotational temperatures and column densities of molecules derived from J = 1-0 and 4-3 lines of HCN and HCO+ and J = 2-1 and 7-6 of CS in the CND and ring were derived. Furthermore, a non-local thermodynamic equilibrium model revealed that the kinetic temperature of T-k = 350-550 K in the CND is higher than T-k = 80-300 K in the ring, utilizing the intensity ratios of HCN, HCO+, and CS. The star-formation efficiency in the CND is almost an order of magnitude lower than those at the spots in the star-forming ring, while the dominant activity of the central region is star formation rather than active galactic nuclei. We determined that the large velocity dispersion of CO extending towards the north side of the CND and decomposing into blueshifted and redshifted features is probably explained by the effect of the radio jets. These results strongly suggest that the jets heat the gas in the CND, in which the feedback prevents star formation.

DOI： 10.1093/pasj/psx076

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

In this study, we present the results of (CO)-C-12(J = 1-0), (CO)-C-13(J = 1-0), and (CO)-O-18(J = 1-0) simultaneous observations of the dwarf galaxy NGC2976 conducted as a part of the CO Multi-line Imaging of Nearby Galaxies (COMING) project using the Nobeyama 45 m telescope. We investigated the properties of the molecular gas and star formation in NGC2976. We found that the molecular gas fraction depends on the surface densities of the total gas and the star formation rate, according to the main stellar disks of spiral galaxies. The ratio of (CO)-C-12(J = 3-2) to (CO)-C-12(J = 1-0) implies that the temperature of the molecular gas increases with decreases in the surface density of molecular gas. We detected (CO)-C-13(J = 1-0) by using the stacking method. The ratio between the integrated intensities of (CO)-C-12(J = 1-0) and (CO)-C-13(J = 1-0) was 27 +/- 11. These ratios imply that the diffuse gas phase is dominant in low surface density regimes. We obtained a lower limit of the ratio between the integrated intensities of (CO)-C-12(J = 1-0) and (CO)-O-18(J = 1-0) of 21. The relation between the surface densities of the total gas and the star formation rate followed a power-law index of 2.08 +/- 0.11, which was larger than that between the surface densities of the molecular gas and the star formation rate (1.62 +/- 0.17). The steep slope in the relation between the surface densities of the total gas and the star formation rate can be attributed to the rapid increase in the fraction of molecular gas at the surface density of similar to 10M(circle dot). The kinematics of the molecular gas suggest that the bar-like feature rotates with a rigid-body rotation curve rather than a certain pattern speed.

DOI： 10.1093/pasj/psx044

Web of Science

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

We have investigated properties of the interstellar medium in interacting galaxies in early and mid stages using mapping data of <SUP>12</SUP>CO(J = 1-0) and H i. Assuming the standard CO-H<SUB>2</SUB> conversion factor, we found no difference in molecular gas mass, atomic gas mass, and total gas mass (the sum of atomic and molecular gas mass) between interacting galaxies and isolated galaxies. However, interacting galaxies have a higher global molecular gas fraction f_{mol}^{global} (the ratio of molecular gas mass to total gas mass averaged over a whole galaxy) at 0.71 ± 0.15 than isolated galaxies (0.52 ± 0.18). The distribution of the local molecular gas fraction f<SUB>mol</SUB>, the ratio of the surface density of molecular gas to that of the total gas, is different from the distribution in typical isolated galaxies. By a pixel-to-pixel comparison, isolated spiral galaxies show a gradual increase in f<SUB>mol</SUB> along the surface density of total gas until it is saturated at 1.0, while interacting galaxies show no clear relation. We performed pixel-to-pixel theoretical model fits by varying metallicity and external pressure. According to the model fitting, external pressure can explain the trend of f<SUB>mol</SUB> in the interacting galaxies. Assuming half of the standard CO-H<SUB>2</SUB> conversion factor for interacting galaxies, the results of pixel-to-pixel theoretical model fitting get worse than adopting the standard conversion factor, although f_{mol}^{global} of interacting galaxies (0.62 ± 0.17) becomes the same as in isolated galaxies. We conclude that external pressure occurs due to the shock prevailing over a whole galaxy or due to collisions between giant molecular clouds even in the early stage of the interaction. The external pressure accelerates an efficient transition from atomic gas to molecular gas. Regarding the chemical timescale, high f<SUB>mol</SUB> can be achieved at the very early stage of interaction even if the shock induced by the collision of galaxies ionizes interstellar gas. <P />...

DOI： 10.1093/pasj/psx041

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

A new method to discover obscured active galactic nuclei (AGNs) by utilizing X-ray and infrared data has recently been developed. We carried out a survey of H2O maser emission toward 10 obscured AGNs with the Nobeyama 45 m telescope. We newly detected the maser emission with a signal-noise-ratio (SNR) of above 4 from two AGNs; NGC 1402 and NGC 7738. We also found a tentative detection with SNR &gt; 3 in NGC 5037. The detection rate of 20% is higher than those of previous surveys (usually several percent).

DOI： 10.1093/pasj/psx052

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We carried out line survey observations at the 26-30 GHz band toward the four high-mass star-forming regions containing hot cores, G10.30-0.15, G12.89+0.49, G16.86-2.16, and G28.28-0.36, with the Robert C. Byrd Green Bank Telescope. We have detected HC5N from all of the sources, and HC7N from the three sources, except for G10.30-0.15. We further conducted observations of HC5N at the 42-46 GHz and 82-103 GHz bands toward the three sources, G12.89+0.49, G16.86-2.16, and G28.28-0.36, with the Nobeyama 45 m radio telescope. The rotational lines of HC5N with the high-excitation energies (E-u/k similar to 63-100 K), which are hardly excited in the cold dark clouds, have been detected from the three sources. The rotational temperatures of HC5N are found to be similar to 13-20 K in the three sources. The detection of the lines with the high-excitation energies and the derived rotational temperatures indicate that HC5N exists in the warm gas within 0.07-0.1 pc radii around massive young stellar objects. The column densities of HC5N in the three sources are derived to be (similar to 2.0-2.8) x 1013 cm(-2). We compare the ratios between N(HC5N) the column density of HC5N and W(CH3OH) the integrated intensity of the thermal CH3OH emission line among the three high-mass star-forming regions. We found a possibility of the chemical differentiation in the three high-mass star-forming regions; G28.28-0.36 shows the largest N(HC5N)/W(CH3OH) ratio of&gt;8.0 x 10(14) in units of (Kkms (1)) (1)cm (2), while G12.89+0.49and G16.86-2.16 show the smaller values (similar to 2 x 10(13)).

DOI： 10.3847/1538-4357/aa7899

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC 147, NGC 185 and NGC 205). Ancillary HI, CO, Spitzer Infrared Spectrograph spectra, Ha and X-ray observations are combined to trace the atomic, cold and warm molecular, ionized and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [CI] observations of NGC 205 to revise its molecular gas content. We derive total gas masses of M-g = 1.9-5.5 x 10(5) M-circle dot for NGC 185 and Mg = 8.6-25.0 x 10(5) M-circle dot for NGC 205. Non-detections combine to an upper limit on the gas mass of Mg = 0.3-2.2 x 10(5) M-circle dot for NGC 147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR similar to 37-107 and 48-139 are also considerably lower compared to the expected GDR similar to 370 and 520 for the low metal abundances in NGC 185 (0.36 Z(circle dot)) and NGC 205 (0.25 Z(circle dot)), respectively. To simultaneously account for the gas deficiency and low gas-todust ratios, we require an efficient removal of a large gas fraction and a longer dust survival time (similar to 1.6 Gyr). We believe that efficient galactic winds (combined with heating of gas to sufficiently high temperatures in order for it to escape from the galaxy) and/or environmental interactions with neighbouring galaxies are responsible for the gas removal from NGC 147, NGC 185 and NGC 205.

DOI： 10.1093/mnras/stw3001

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present high-resolution (1 0) Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO (1-0) and CO (2-1) rotational transitions toward the nearby IR-luminous merger NGC 1614 supplemented with ALMA archival data of CO (3-2). and CO (6-5) transitions. The CO. (6-5) emission arises from the starburst ring (central 590 pc in radius), while the lower-J CO lines are distributed over the outer disk (similar to 3.3 kpc in radius). Radiative transfer and photon- dominated region (PDR) modeling reveals that the starburst ring has a single warmer gas component with more a intense far-ultraviolet radiation field (n(H2) similar to 10(4.6) cm(-3), T-kin similar to 42 K, and G(0) similar to 10(2.7)) relative to the outer disk (n(H2) similar to 10(5.1) cm(-3), T-kin similar to 22 K, and G(0) similar to 10(0.9)). A two-phase molecular interstellar medium with a warm and cold (&gt; 70 and similar to 19 K) component is also an applicable model for the starburst ring. A possible source for heating the warm gas component is mechanical heating due to stellar feedback rather than PDR. Furthermore, we find evidence for non-circular motions along the north-south optical bar in the lower-J CO images, suggesting a cold gas inflow. We suggest that star formation in the starburst ring is sustained by the bardriven cold gas inflow. and that starburst activities radiatively and mechanically power the CO excitation. The absence of a bright active galactic nucleus can be explained by a scenario where. cold gas accumulating on the starburst ring is exhausted as the fuel for star formation. or is launched as an outflow before being able to feed to the nucleus.

DOI： 10.3847/1538-4357/835/2/174

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Language：English   Publisher：IOP PUBLISHING LTD  

DOI： 10.3847/1538-4357/834/1/97

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press  

In the article [PASJ 64, 133 (2012)], the 12CO (J = 1-0) intensity was mistakenly multiplied by a factor of 1.61. Therefore, the 12CO (J = 1-0) integrated intensity ICO(J = 1-0) and the ICO(J = 3-2)-to-ICO(J = 1-0) integrated intensity ratio R3-2/1-0 should be corrected. In addition, two giant molecular clouds (GMCs) were missing from table 1, because we overlooked them when making a list of GMCs from the identified GMC data. Moreover, the spectrum of the GMC No. 49 in figure 2 was wrong. Accordingly, the tables, the figures and figure captions are corrected as shown below. Note that the GMC mass MH2 in table 1 remains unchanged. The two missing GMCs are added to table 1 as GMC No.75 and No. 76. These errors do not affect conclusions 2 and 3. The following sentences should be corrected as follows: the first line of the abstract should be replaced with "...emission of 76 major giant molecular clouds..."
the paragraph in the fifth line of the abstract is replaced with "We detect 12CO(J = 3-2) emission of 67 GMCs successfully."
the beginning of the first sentence of the last paragraph of section 2 is replaced with "We successfully determined 76 GMCs..."
the beginning of the first sentence of the second paragraph of subsection 3.1 is replaced with "Among the 76 GMCs..."
the third sentence of subsection 3.2 should be ended with "... from less than 0.1 to 1.19."
the next sentence should be ended with "... the R3-2/1-0 mean is 0.41."
the sentences in the middle of subsection 3.2 is replaced with "The GMCs we detected are predominantly located in spiral arms. The R3-2/1-0 value is equivalent to that of the arm region of the Milky Way galaxy (∼0.4: Oka et al. 2007). A GMC with a remarkably high R3-2/1-0 value of 1.19 (No.13) is located..."
the fourth sentence of the second paragraph of subsection 4.2 should end with "..., we devide the sample in half at MH2 = 8.0 × 104 M⊙." Because the two missing GMCs are added to the sample, the value to divide the sample in half should be changed
the last two sentences of the second paragraph of subsection 4.2 should be "The averages of R3-2/1-0 are 0.52 for the 16 less-massive and star-forming GMCs, 0.58 for the 23 massive and star-forming GMCs, and 0.38 for the 15 massive and low star-forming GMCs. It should be noted that R3-2/1-0 = 0.23 for the 22 less star-forming, less-massive GMCs is a value averaged over upper-limit values."
the third sentence of the third paragraph of subsection 4.2 is replaced with "We found that ∼26% of the GMCs with MH2 &lt
8.0 × 104 M⊙ show R3-2/1-0 ≤ 0.1, whereas none of the GMCs with MH2 &gt
8.0 × 104 M⊙ have such a small value of R3-2/1-0."
the fifth sentence of the third paragraph of subsection 4.2 is replaced with "... the difference between the mean upper-limit value of 0.23 for less star-forming, less-massive GMCs and the mean value of 0.38 for less star-forming, massive GMCs is significant: ..."
the last sentence of the third paragraph of subsection 4.2 is replaced with "... the difference between the average values of R3-2/1-0, i.e., 0.52 and 0.58, is comparable with the measurement uncertainties."
the first two sentences of section 5 should be "We identified 76 GMCs from our 12CO (J = 1-0) data of M 33. Among these, 12CO (J = 3-2) emission of 67 GMCs are detected."
the first conclusion should be replaced with "The 12CO (J = 1-0) and 12CO (J = 3-2) integrated intensity ratio R3-2/1-0 is spread over a wide range from less than 0.1 to 1.19, having a weighted mean of R3-2/1-0 = 0.41. This weighted mean is equivalent to that of the quiescent disk region of the Milky Way."

DOI： 10.1093/pasj/psx016

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the new single-dish CO (3-2) emission data obtained toward 19 early-stage and 7 late-stage nearby merging galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). Combining with the single-dish and interferometric data of galaxies observed in previous studies, we investigate the relation between the CO (3-2) luminosity (LCO(3-2)') and the far-infrared luminosity (L-FIR) in a sample of 29 early-stage and 31 late-stage merging galaxies, and 28 nearby isolated spiral galaxies. We find that normal isolated spiral galaxies and merging galaxies have different slopes (alpha) in the log LCO(3-2)'-log L-FIR plane (alpha similar to 0.79 for spirals and similar to 1.12 for mergers). The large slope (alpha &gt; 1) for merging galaxies can be interpreted as evidence for increasing star formation efficiency (SFE = L-FIR/LCO(3-2)') as a function of L-FIR. Comparing our results with sub-kpc-scale local star formation and global starburst activity in the high-z universe, we find deviations from the linear relationship in the log LCO(3-2)'-log L-FIR plane for the late-stage mergers and high-z star-forming galaxies. Finally, we find that the average SFE gradually increases from isolated galaxies to merging galaxies and to highz submillimeter galaxies/quasi-stellar objects. By comparing our findings with results from numerical simulations, we suggest that: (1) inefficient starbursts triggered by disk-wide dense clumps occur in the early stage of interaction, and (2) efficient starbursts triggered by central concentration of gas occur in the final stage. A systematic high spatial resolution survey of diffuse- and dense-gas tracers is the key to confirming this scenario.

DOI： 10.1093/pasj/psw087

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present survey data of six NH3 (J, K) = (1, 1), (2, 2), (3, 3), (4, 4), (5, 5), and (6, 6) lines, simultaneously observed with the Tsukuba 32 m telescope, in the main part of the central molecular zone of the Galaxy. The total number of on-source positions was 2655. The three lower transitions were detected with S/N &gt; 3 at 2323 positions (93% of all the on-source positions). Among 2323, the S/N's of (J, K) = (4, 4), (5, 5), and (6, 6) exceeded 3.0 at 1426(54%), 1150(43%), and 1359(51%) positions, respectively. Simultaneous observations of the lines enabled us to accurately derive intensity ratios with less systematic errors. Boltzmann plots indicate that there are two temperature components: cold (similar to 20 K) and warm (similar to 100 K). Typical intensity ratios of T-mb (2, 2)/T-mb(1, 1), T-mb(4, 4)/T-mb(2, 2), T-mb(5, 5)/T-mb(4, 4), and T-mb(6, 6)/T-mb(3, 3) were 0.71, 0.45, 0.65, and 0.17, respectively. These line ratios correspond to the diversity of the rotational temperature, which results from mixing of the two temperature components.

DOI： 10.1093/pasj/psw072

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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.

DOI： 10.1093/pasj/psw080

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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.

DOI： 10.1093/pasj/psv134

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We present the results of Atacama Large Millimeter/Submillimeter Array (ALMA) 108-, 233-, 352-, and 691-GHz continuum observations and Very Large Array (VLA) 4.81-and 8.36-GHz observations of the nearby luminous merger remnant NGC1614. By analyzing the beam (1.'' 0 x 1.'' 0) and uv (&gt;= 45 k lambda) matched ALMA and VLA maps, we find that the deconvolved source size of lower-frequency emission (&lt;= 108 GHz) is more compact (420 pc x 380 pc) compared to the higher-frequency emission (&gt;= 233 GHz) (560 pc x 390 pc), suggesting different physical origins for the continuum emission. Based on a spectral energy distribution (SED) model for a dusty starburst galaxy, it is found that the SED can be explained by three components: (1) non-thermal synchrotron emission (traced in the 4.81-and 8.36-GHz continua), (2) thermal free-free emission (traced in the 108-GHz continuum), and (3) thermal dust emission (traced in the 352-and 691-GHz continua). We also present the spatially resolved (sub-kpc scale) Kennicutt-Schmidt relation of NGC1614. The result suggests a systematically shortermolecular gas depletion time in NGC1614 (average tau(gas) of 49-77 Myr and 70-226 Myr at the starburst ring and the outer region, respectively) than that of normal disk galaxies (similar to 2 Gyr) and a mid-stage merger VV 114 (= 0.1-1 Gyr). This implies that the star formation activities in (ultra-) luminous infrared galaxies are efficiently enhanced as the merger stage proceeds, which is consistent with the results from high-resolution numerical merger simulations.

DOI： 10.1093/pasj/psv136

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We report the development of the new 4-beam, 2-polarization, 2-sideband, 100 GHz band SIS receiver "FOREST" (FOur beam REceiver System on the 45-m Telescope) and the results from commissioning and observations on the Nobeyama 45-m Telescope operated by Nobeyama Radio Observatory, a branch of National Astronomical Observatory of Japan. FOREST aims to add new capabilities of large-area mapping and simultaneous multi-line observation at 80 - 116 GHz band to the Nobeyama 45-m Telescope, which is one of the largest millimeter radio telescopes in the world. The configuration of the four beams is a quadrate of 2 x 2 with the separation between adjacent beams of 50". Beam size of each beam is 15" at 115 GHz. Receiver noise temperature is as low as that of ALMA Band 3 receivers, so that mapping speed is more than four times as high as that of the other 100 GHz band receivers on the 45-m Telescope. The IF bandwidth is 8 GHz (4 - 12 GHz) realizing simultaneous (CO)-C-12 (J = 1 0), (CO)-C-13 (J = 1 0), and (CO)-O-18(J = 1 - 0) observations. Cooled components inside of cryostat are modularized per beam. IF signals from the cryostat are processed by the room temperature IF system, and then passed to spectrometers. We have installed the FOREST receiver into the Nobeyama 45-m Telescope, evaluated its performance, and made large area mapping observations. These demonstrate the excellent performance of the FOREST receiver and the Nobeyama 45-m Telescope.

DOI： 10.1117/12.2232137

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：CAMBRIDGE UNIV PRESS  

We present high resolution molecular line observations of dusty AGN and star burst in nearby luminous infrared galaxies (LIRGs), VV 114 (band 3/4/7) and NGC 1614 (band 3/6/7/9), with ALMA. Multi-frequency imaging from 4.8 GHz to 691 GHz of NGC 1614 allows us to study spatial properties of the radio-to-FIR continuum and multiple CO transitions, and we find the CO excitation up to J(upp) = 6 can be explained by a single ISM model powered by nuclear starbursts. Our processing line imaging survey for VV 114 detected at least 30 molecular lines which show different chemical composition from region to region. Multi-molecule imaging helps us to diagnose the chemical differences of dusty ISM, while multi-transition imaging allows us to investigate gas physical conditions affected by nuclear activities directly.

DOI： 10.1017/S1743921316008334

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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.

DOI： 10.1088/0004-637X/815/1/59

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Publishing type：Research paper (scientific journal)  

DOI： 10.5303/PKAS.2015.30.2.649

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In order to explore any change caused by the G2 cloud approaching, we have monitored the flux density of Sgr A* at 22 GHz from 2013 February to 2014 August with a sub-array of the Japanese Very Long Baseline Interferometry Network. The observation period included the expected periastron dates. The number of observation epochs was 283 days. We have observed no significant microwave enhancement of Sgr A* in the whole observation period. The average flux density in the period is S-nu = 1.23 +/- 0.33 Jy. The average is consistent with the usually observed flux density range of Sgr A* at 22 GHz.

DOI： 10.1088/2041-8205/798/1/L6

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ASTRONOMICAL SOC PACIFIC  

Giant Molecular Clouds (GMCs) and Giant Molecular Associations (GMAs) are origins of massive stars. Recently, it is suggested that the evolution of GMCs and GMAs in spiral galaxies is greatly influenced by the galactic dynamics, especially kinetic shear motion, due to the arms. We have derived velocity vectors of the molecular gas in spiral galaxies and investigated the influence of shear motion on the evolution of GMAs, where the shear motion in the galactic disk was determined from the velocity vectors. The distributions of GMAs and the shear strength due to the differential rotation show the anti-correlation with each other. In addition to the cutoff in number counts of GMAs in strong shear regions, the existences of GMAs only in the area of the weak shear strength and further on the upstream side of high shear strength suggest that GMAs are fragmented into GMCs by the shear, although surviving in the weak shear.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ASTRONOMICAL SOC PACIFIC  

We present the results of ALMA Cycle 1 observations toward interacting galaxies in the early stage of the interaction, VV 219. A map of (CO)-C-12(J = 1-0) obtained with the ACA 7-m array represents that there is a large giant molecular association at the colliding region of the progenitor galaxies. Since this structure is resolved out with 12-m array data, it is at least as large as 155 pc which is larger than typical giant molecular associations. The velocity dispersion of this giant molecular association is broader than surrounding region by about 5 km s(-1) These fact implies that progenitors are colliding at this region and this collision of gas clouds may trigger star formation.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ASTRONOMICAL SOC PACIFIC  

We present high resolution (0 ''.2 - 2 ''.0) ALMA cycle 2 observations of the IR-bright mid-stage merger VV 114 (band 3), the minor merger NGC 1614 (band 3/6), and the early-stage merger NGC 3110 (band 3), which are supplemented with the cycle 0 observations of VV 114 (band 3/7) and NGC 1614 (band 7/9). These observations include the CO (1-0), CO (2-1), (CO)-C-13 (1-0), (CO)-C-13 (2-1), CO (3-2), CO (6-5), HCN (4-3), and HCO+ (4-3) emission as well as continuum emission. We find that VV 114 has a multi-phase ISM (e.g., extended CO arms [similar to 10 kpc], a (CO)-C-13 filament [similar to 6 kpc], and compact HCN sources [&lt; 200 pc]), while NGC 1614 shows a rotating molecular ring with the radius of 240 pc, which is detected in the all molecular lines above. NGC 3110 shows two asymmetric molecular spiral arms and a strong bar. The CN (1-0), (CO)-O-18 (2-1), CS (2-1), and CH3OH (2-1) emission are also detected. Diagnosing detected lines using line intensity ratios, we suggest that an AGN, starbursts, and shocks are important drivers of the chemistry of VV 114, while merger and bar-induced starburst activities dominate the chemistry of NGC 1614 and NGC 3110, respectively.

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We present < 1 kpc resolution CO imaging study of 37 optically-selected local
merger remnants using new and archival interferometric maps obtained with ALMA,
CARMA, SMA and PdBI. We supplement a sub-sample with single-dish measurements
obtained at the NRO 45 m telescope for estimating the molecular gas mass (10^7
- 10^11 M_sun), and evaluating the missing flux of the interferometric
measurements. Among the sources with robust CO detections, we find that 80 %
(24/30) of the sample show kinematical signatures of rotating molecular gas
disks (including nuclear rings) in their velocity fields, and the sizes of
these disks vary significantly from 1.1 kpc to 9.3 kpc. The size of the
molecular gas disks in 54 % of the sources is more compact than the K-band
effective radius. These small gas disks may have formed from a past gas inflow
that was triggered by a dynamical instability during a potential merging event.
On the other hand, the rest (46 %) of the sources have gas disks which are
extended relative to the stellar component, possibly forming a late-type galaxy
with a central stellar bulge. Our new compilation of observational data
suggests that nuclear and extended molecular gas disks are common in the final
stages of mergers. This finding is consistent with recent major-merger
simulations of gas rich progenitor disks. Finally, we suggest that some of the
rotation-supported turbulent disks observed at high redshifts may result from
galaxies that have experienced a recent major merger.

DOI： 10.1088/0067-0049/214/1/1

arXiv

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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, Sigma H-2, and the star formation rate surface density, Sigma(SFR). This result is based on wide-field and high-sensitivity CO(3-2) observations at 100 pc resolution. Star formation efficiencies (SFEs), defined as Sigma(SFR)/Sigma H-2, in GHRs are found to be similar to 1 dex higher than in other disk regions. The CO(3-2)/CO(1-0) integrated intensity ratio, R3-2/1-0, is also higher than the average over the disk. Such high SFEs and R3-2/1-0 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(H-2) conversion factor, (2) the dense gas fraction traced by R3-2/1-0, 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(H-2) conversion factor.

DOI： 10.1088/0004-637X/788/2/167

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Cambridge University Press  

Our new compilation of interferometric CO data suggests that nuclear and extended molecular gas disks are common in the final stages of mergers. Comparing the sizes of the molecular gas disk and gas mass fractions to early-type and late-type galaxies, about half of the sample show similar properties to early-type galaxies, which have compact gas disks and low gas mass fractions. We also find that sources with extended gas disks and large gas mass fractions may become disk-dominated galaxies.

DOI： 10.1017/S1743921314009879

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of the International Astronomical Union  

DOI： 10.1017/S1743921314000969

Scopus

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Authorship：Lead author   Language：English  

We performed <SUP>12</SUP>CO(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. <P />...

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We present observational evidence for forming a molecular gas disk in merging galaxies using new and archival interferometric CO maps of 37 optically selected merger remnants in the local universe. We found that 65% (24/37) of the merger remnants sample shows kinematical signatures of a rotating disk in the interferometer maps. The sources with an extended CO disk have high FIR luminosities (̃ 10<SUP>11</SUP> L<SUB>☉</SUB>), which suggests that active star formation takes place in the extended CO disks and stellar disks will be possibly formed. The molecular gas-to-stellar mass ratio for merger remnants is larger than that of the stellar mass matched early-type galaxies. However, there is no significant evidence suggesting that the high gas mass ratio leads to a more efficient formation of a molecular gas disk....

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We present results of <SUP>12</SUP>CO(J = 1-0) observations using NRO 45m radio telescope toward four interacting galaxies in the early and the mid stage of the <P />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. <P />...

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We present preliminary results from our ongoing single-dish and interferometric molecular gas survey toward a sample of optically selected merger remnants. We show structural and kinematical evidence that a significant fraction of merger remnants form rotating molecular disks around their central remnants, and that the size of the resultant disks in some of the galaxies are larger compared to the central bulge size inferred from the Sersic radius. The high occurrence of disks in merger remnants may support the evolutionary scenario where major mergers can evolve into a variety of Hubble types....

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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 10<SUP>9</SUP>-10<SUP>6</SUP> M☉ yr<SUP>-1</SUP>pc<SUP>-2</SUP> among GMCs, while <SUP>12</SUP>CO(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 <SUP>12</SUP>CO(J=1-0) data, and detected <SUP>12</SUP>CO(J=3-2) emission in 65 GMCs among them. We find that the correlation between the <SUP>12</SUP>CO(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 <SUP>12</SUP>CO(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 R<SUB>3-2/1-0</SUB>. Moreover, we also observe a mass-dependent trend of R<SUB>3-2/1-0</SUB> for the GMCs with a low star-forming activity. From these results, we speculate that the R<SUB>3-2/1-0</SUB> 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....

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

We present the results of <SUP>12</SUP> CO (J = 1-0) mapping observations toward four interacting galaxies in early and mid stages of the interaction in order to understand the behavior of molecular gas in galaxy-galaxy interactions. The observations were carried out using the 45-m telescope at Nobeyama Radio Observatory (NRO). We compared our CO total flux to those previously obtained with single-dish observations, and found that there is no discrepancy between them. By applying a typical CO-H<SUB>2</SUB> conversion factor, it was found that all constituent galaxies have molecular gas mass of more than 10<SUP>9</SUP> M<SUB>☉</SUB>. Comparisons to H I, K<SUB>s</SUB>, and tracers of star formation, such as Hα, FUV, 8 μm, and 24 μm, revealed that the distribution of molecular gas in interacting galaxies in the early stage of the interaction differs from atomic gas, stars, and star-forming regions. These differences can not be explained without the result of the interaction. The central concentration of molecular gas of interacting galaxies in the early stage of the interaction is lower than that of isolated galaxies, which suggests that molecular gas is distributed off-centre, and/or extends in the beginning of the interaction....

DOI： 10.1093/pasj/65.1.20

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report the results of our observations of the (CO)-C-12 (J = 1-0) and (CO)-C-12 (J = 3-2) line emission of 74 major giant molecular clouds (GMCs) within the galactocentric distance of 5.1 kpc in the Local Group galaxy M 33. The observations have been conducted as part of the Nobeyama Radio Observatory M 33 All-disk survey of Giant Molecular Clouds project (NRO MAGiC). The spatial resolutions are 80 pc for (CO)-C-12 (J=1-0) and 100 pc for (CO)-C-12 (J=3-2). We detect (CO)-C-12 (J = 3-2) emission of 65 GMCs successfully. Furthermore, we find that the correlation between the surface density of the star formation rate, which is derived from a linear combination of Ha and 24 mu m emissions, and the (CO)-C-12 (J = 3-2) integrated intensity still holds at this scale. This result shows that the star-forming activity is closely associated with warm and dense gases that are traced with the (CO)-C-12 (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.

DOI： 10.1093/pasj/64.6.133

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present a giant molecular cloud (GMC) catalog of M33, containing 71 GMCs in total, based on wide-field and high-sensitivity CO(J = 3-2) observations with a spatial resolution of 100 pc using the ASTE 10 m telescope. Employing archival optical data, we identify 75 young stellar groups (YSGs) from the excess of the surface stellar density, and estimate their ages by comparing with stellar evolution models. A spatial comparison among the GMCs, YSGs, and H II regions enable us to classify GMCs into four categories: Type A, showing no sign of massive star formation (SF); Type B, being associated only with H II regions; Type C, with both H II regions and &lt;10 Myr old YSGs; and Type D, with both H II regions and 10-30 Myr YSGs. Out of 65 GMCs (discarding those at the edges of the observed fields), 1 (1%), 13 (20%), 29 (45%), and 22 (34%) are Types A, B, C, and D, respectively. We interpret these categories as stages in a GMC evolutionary sequence. Assuming that the timescale for each evolutionary stage is proportional to the number of GMCs, the lifetime of a GMC with a mass &gt;10(5)M(circle dot) is estimated to be 20-40 Myr. In addition, we find that the dense gas fraction as traced by the CO(J = 3-2)/CO(J = 1-0) ratio is enhanced around SF regions. This confirms a scenario where dense gas is preferentially formed around previously generated stars, and will be the fuel for the next stellar generation. In this way, massive SF gradually propagates in a GMC until gas is exhausted.

DOI： 10.1088/0004-637X/761/1/37

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

In order to test a recent hypothesis that the dispersion in the Schmidt-Kennicutt law arises from variations in the evolutionary stage of star-forming molecular clouds, we compared molecular gas and recent star formation in an early-phase merger galaxy pair, Taffy I (UGC 12915/UGC 12914, VV 254) which went through a direct collision 20 Myr ago and whose star-forming regions are expected to have similar ages. Narrowband Pa alpha image is obtained using the ANIR near-infrared camera on the mini-TAO 1 m telescope. The image enables us to derive accurate star formation rates within the galaxy directly. The total star formation rate, 22.2 M-circle dot yr(-1), was found to be much higher than previous estimates. Ages of individual star-forming blobs estimated from equivalent widths indicate that most star-forming regions are similar to 7 Myr old, except for a giant HII region at the bridge which is much younger. Comparison between star formation rates and molecular gas masses for the regions with the same age exhibits a surprisingly tight correlation, a slope of unity, and star formation efficiencies comparable to those of starburst galaxies. These results suggest that Taffy I has just evolved into a starburst system after the collision, and the star-forming sites are at a similar stage in their evolution from natal molecular clouds except for the bridge region. The tight Schmidt-Kennicutt law supports the scenario that dispersion in the star formation law is in large part due to differences in evolutionary stage of star-forming regions.

DOI： 10.1088/0004-637X/757/2/138

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Language：English   Publishing type：Research paper (international conference proceedings)  

We show that the dispersion in the Schmidt-Kennicutt (SK) law in galaxies is affected significantly by the evolutionary stage of star forming molecular gas, using narrow band PA&amp
Alpha
imaging of Taffy I, an interacting pair of galaxies. Star forming regions in the system show very uniform ages except for the bridge region, and the SK law of regions at the same age show a exceptionally tight SK law. © 2013 International Astronomical Union.

DOI： 10.1017/S1743921313001579

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present (CO)-C-13(J = 1-0) line emission observations with the Nobeyama 45-m telescope toward the giant H II region NGC 604 in the spiral galaxy M 33. We detected (CO)-C-13(J = 1-0) line emissions ill 3 major giant molecular clouds (GMCs) labeled as GMC-A, B, and C beginning at the north. We derived two line intensity ratios, (CO)-C-13(J = 1-0)/(CO)-C-12(J = 1-0), R-13/12, and (CO)-C-12(J = 3-2)/(CO)-C-12(J = 1-0), R-31, for each GMC at an angular resolution of 25 '' (100 pc). The averaged values of R-13/12 and R-31 are 0.06 and 0.31 within the whole GMC-A, 0.11 and 0.67 within the whole GMC-B, and 0.05 and 0.36 within the whole GMC-C, respectively. In addition, we obtained R-13/12 = 0.09 +/- 0.02 and R-31 = 0.76 +/- 0.06 at the (CO)-C-12(J = 1-0) peak position of the GMC-B. Under the Large Velocity Gradient approximation, we determined a gas density of 2.8 x 10(3) cm(-3) and a kinetic temperature of 33(-5)(+9) K at the (CO)-C-12(J = 1-0) peak position of the GMC-B. Moreover, we determined 2.5 x 10(3) cm(-3) and 25 +/- 2 K as the averaged values within the whole GMC-B. We concluded that dense molecular gas is formed everywhere in the GMC-B because the derived gas density not only at the peak position of the GMC, but also averaged over the whole GMC, exceeds 10(3) cm(-3). On the other hand, the kinetic temperature averaged over the whole GMC-B, 25 K. is significantly lower than that at the peak position, 33 K. This is because the H II regions are lopsided to the northern part of the GMC-B; thus, OB stars can heat only the northern part, including the (CO)-C-12(J = 1-0) peak position, of this GMC.

DOI： 10.1093/pasj/64.1.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the results of the Nobeyama Radio Observatory (NRO) M 33 All-Disk (30' x 30' or 7.3 kpc x 7.3 kpc) Survey of Giant Molecular Clouds (NRO MAGiC) based on (CO)-C-12 (J = 1-0) observations using the NRO 45 m telescope. The spatial resolution of the resultant map is 19 ''.3, corresponding to 81 pc, which is sufficient to identify each Giant Molecular Cloud (GMC) in the disk. We found clumpy structures with a typical spatial scale of similar to 100 pc, corresponding to GMCs, and no diffuse, smoothly distributed component of molecular gas at this sensitivity. The overall distribution of molecular gas roughly agrees with that of HI. However, a closer inspection of the CO and H maps suggests that not every CO emission is associated with local H I peaks, particularly in the inner portion of the disk (r &lt; 2 kpc), although most of the CO emission is located at the local H I peaks in the outer radii. We found that most uncovered GMCs are accompanied by massive star-forming regions, although the star-formation rates (SFRs) vary widely from cloud to cloud. The surface density of the azimuthally averaged H I gas exhibits a flat radial distribution. However, the CO radial distribution shows a significant enhancement within the central 1-2 kpc region, which is very similar to that of the SFR. We obtained a map of the molecular fraction, f(mol) = Sigma(H2)/(Sigma(HI) + Sigma(H2)), with a resolution of 100 pc. This is the first f(mol) map covering an entire galaxy with a GMC-scale resolution. We found that f(mol) tends to be high near the center. The correlation between f(mol) and gas surface density shows two distinct sequences. The presence of two correlation sequences can be explained by a difference of metallicity; i.e., higher (similar to 2-fold) metallicity in the central region (r &lt; 1.5 kpc) than in the outer parts. Alternatively, difference in the scale height can also account for the two sequences; i.e., the scale height increases at the outer disk.

DOI： 10.1093/pasj/63.6.1171

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Language：English   Publishing type：Research paper (international conference proceedings)  

We developed a new observing system to improve the performance of the 45-m telescope at Nobeyama Radio Observatory (NRO). The system consists of new receivers, new IF converters, new A/D converters, and a new spectrometer. The technologies developed for ALMA (the Atacama Large Millimeter/Submillimeter Array) were used for many parts (e.g., receivers and spectrometers). With the new system, we are conducting surveys of distant primeval galaxies and line surveys of various targets. © 2011 IEEE.

DOI： 10.1109/URSIGASS.2011.6051296

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Language：English   Publishing type：Research paper (scientific journal)  

As the Nobeyama Radio Observatory Legacy Project: Survey of Giant Molecular Clouds in M33, we have been mapping M33 in CO(1-0) with the multi-beam receiver BEARS equipped on the 45-m telescope using the OTF mapping technique since 2007. The purpose of this project is to investigate the physical properties of GMCs and understand the evolutionary process from GMC formation to star formation in GMCs by comparing with various data such as CO(3-2), 1.1 mm continuum obtained with ASTE10m telescope at Atacama and the optical data obtained with SUBARU. We identified 87 GMCs using the first year data of CO(1-0) and observed 28 GMCs among them in CO(3-2) with ASTE (Onodera 2009, PhD thesis, University of Tokyo). From the comparison of these lines, it was shown that the CO(3-2)/CO(1-0) ratio increases with star forming activity in the GMCs. Furthermore, we found that more massive GMCs tend to have higher CO(3-2)/CO(1-0) ratio. Since the ratio is thought to be an indicator of the fraction of warm and dense molecular gas, our results imply that the fraction of warm and dense gas increases with GMC mass. Especially, since the ratio in the GMCs with low star forming activity is in the range where the ratio depends mainly on the density, we speculate that dense gas fraction increases with GMC mass. <P />...

DOI： 10.1017/S1743921310010045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have mapped the northern area (30&apos; x 20&apos;) of a Local Group spiral galaxy M33 in (12)CO(J = 1-0) line with the 45 m telescope at the Nobeyama Radio Observatory. Along with H alpha and Spitzer 24 mu m data, we have investigated the relationship between the surface density of molecular gas mass and that of star formation rate (SFR) in an external galaxy (Kennicutt-Schmidt law) with the highest spatial resolution (similar to 80 pc) to date, which is comparable to scales of giant molecular clouds (GMCs). At positions where CO is significantly detected, the SFR surface density exhibits a wide range of over four orders of magnitude, from Sigma(SFR) less than or similar to 10(-10) to similar to 10(-6) M(circle dot) yr(-1) pc(-2), whereas the Sigma(H2) values are mostly within 10-40 M(circle dot) pc(-2). The surface density of gas and that of SFR correlate well at an similar to 1 kpc resolution, but the correlation becomes looser with higher resolution and breaks down at GMC scales. The scatter of the Sigma(SFR)-Sigma(H2) relationship in the similar to 80 pc resolution results from the variety of star-forming activity among GMCs, which is attributed to the various evolutionary stages of GMCs and to the drift of young clusters from their parent GMCs. This result shows that the Kennicutt-Schmidt law is valid only in scales larger than that of GMCs, when we average the spatial offset between GMCs and star-forming regions, and their various evolutionary stages.

DOI： 10.1088/2041-8205/722/2/L127

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ASTRONOMICAL SOC PACIFIC  

We present the results of (CO)-C-12(J=1-0) observations with the NRO 45m radio telescope of the interacting galaxy pair NGC 4567/8, known to be in the early stage of the interaction. Our goal is to investigate the influence of the interaction of galaxies on molecular gas in the early stage. This is the first CO observations covering the whole system for this galaxy pair. Their CO and HI gas distributions suggest NGC 4567/8 are surely colliding. We found high molecular gas fraction, f(mol) and high star formation efficiency (SFE) in their overlap region though the low surface density of molecular gas is low. The discrepancy of the regions with high f(mol) and high SFE may be reflecting the progression of the interaction.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

A non-LTE analysis of K I resonance lines at 7664.91 and 7698.97 angstrom was carried out for 15 red giants belonging to three globular clusters of different metallicity (M 4, M 13, and M 15) along with two reference early-K giants (p Boo and a Boo), in order to check whether the K abundances are uniform within a cluster, and to investigate the behavior of the [K/Fe] ratio at the relevant metallicity range of -2.5 [Fe/H] less than or similar to -1. We confirmed that [K/H] (as well as [Fe/H]) is almost homogeneous within each cluster to a precision of less than or similar to 0.1 dex, though dubiously large deviations are exceptionally seen for two peculiar stars showing signs of considerably increased turbulence in the upper atmosphere. The resulting [K/Fe] ratios are mildly supersolar by a few tenths of dex for three clusters, tending to gradually increase from similar to 0.1-0.2 at [Fe/H] similar to -1 to similar to +0.3 at [Fe/H] similar to -2.5. This result connects reasonably well with the [K/Fe] trend of disk stars (-1 less than or similar to [Fe/H]) and that of extremely metal-poor stars (-4 less than or similar to [Fe/H.] less than or similar to -2.5). That is, [K/Fe] appears to continue a gradual increase from [Fe/H] similar to 0 toward a lower metallicity regime down to [Fe/H] similar to -3, where a broad maximum of [K/Fe] similar to +0.3-0.4 is attained, possibly followed by a slight downturn at [Fe/H] less than or similar to -3.

DOI： 10.1093/pasj/61.3.563

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：The Astronomer's Telegram  

We have started monitor observations of Sgr A* with a short-baseline VLBI(Mizusawa10-m RT, Takahagi32-m RT, Tsukuba32-m RT, and Gifu11-m RT) which is a subset of the Japanese VLBI Network in order to search the increase of 22-GHz emission from Sgr A* induced by the interaction of the G2 cloud with the accretion disk (Gillessen et al. 2012, Nature, 481, 51)....

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Language：English   Publisher：CAMBRIDGE UNIV PRESS  

We have conducted all disk imaging of M33 in (CO)-C-12(1-0) using the 45-m telescope at :Nobeyama Radio Observatory. We present preliminary results of this project. The spatial resolution of similar to 80 pc is comparable to the size of GMCs. The identified GMCs show wide variety in star forming activity. The variety can be regarded as the difference of their evolutionary stage. We found that Kennicutt-Schmidt law breaks in GMC scale (similar to 80 pc), although it is still valid in 1 kpc scale. The correlation between molecular gas fraction, f(mol) = Sigma(H-2)/Sigma(HI+H-2) and gas surface density shows two distinct sequences and shows that f(mol) tends to be higher near the center. We also made partial mapping (CO)-C-12(3-2) with ASTE telescope. These data show that the variation of physical properties of molecular gas are correlated with the GMC evolution and mass. That is, GMCs with more active star formation and more mass tend to have higher fraction of dense gas.

DOI： 10.1017/S1743921311022484

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