Language：Japanese   Publisher：Publications of the Astronomical Society of Japan  

DOI： 10.1093/pasj/psaa116

Scopus

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

We analyze molecular-gas formation in neutral atomic hydrogen (H i) clouds using the latest CO data, obtained from the FOREST (four-beam receiver system on the 45 m telescope) unbiased Galactic plane imaging survey with the Nobeyama 45 m telescope, and using H i data taken from the Very Large Array Galactic plane survey. We applied a dendrogram algorithm to the H i data cube to identify H i clouds, and we calculated the H i mass and molecular-gas mass by summing the CO line intensity within each H i cloud. On the basis of the results, we created a catalog of 5737 identified H i clouds with local standard of rest (LSR) velocity of VLSR ≤-20 km s-1 in galactic longitude and latitude ranges of 20° ≤ l ≤ 50° and-1° ≤ b ≤ 1°, respectively. We found that most of the H i clouds are distributed within a Galactocentric distance of 16 kpc, and most of them are in the cold neutral medium phase. In addition, we determined that the high-mass end of the H i mass function is fitted well with a power-law function with an index of 2.3. Although two sequences of self-gravitating and diffuse clouds are expected to appear in the M tot-$M-{\,{\rm H}-2}$ diagram according to previous works based on a plane-parallel model, the observational data show only a single sequence with large scattering within these two sequences. This implies that most of the clouds are mixtures of these two types of clouds. Moreover, we suggest the following scenario of molecular-gas formation: An H i-dominant cloud evolved with increasing H2 mass along a path of $M-{\,{\rm H}-2} \propto M-{\,\rm tot}^2$ by collecting diffuse gas before reaching and moving along the curves of the two sequences.

DOI： 10.1093/pasj/psaa027

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

We present a method for determining the directions of magnetic-field vectors in a spiral galaxy using two synchrotron polarization maps, an optical image, and a velocity field. The orientation of the transverse magnetic field is determined with a synchrotron polarization map of a higher-frequency band, and the 180°-ambiguity is solved by using a sign of Rotation Measure (RM) after determining the geometrical orientation of a disk based on an assumption of trailing spiral arms. The advantage of this method is that the direction of a magnetic vector for each line of sight throughout the galaxy can inexpensively be determined, with easily available data and simple assumptions. We applied this method to three nearby spiral galaxies using archival data obtained with a Very Large Array (VLA) to demonstrate how it works. The three galaxies have both clockwise and counterclockwise magnetic fields, which implies that none of the three galaxies is classified in a simple Axis-Symmetric type, but types of higher modes, and that magnetic reversals commonly exist.

DOI： 10.3390/galaxies7010032

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astronomical Society of Japan  

We present newly obtained three-dimensional gaseous maps of the Milky Way Galaxy: H I, H2, and total-gas (H I plus H2) maps, which were derived from the H I and 12CO(J = 1-0) survey data and rotation curves based on the kinematic distance. The H I and H2 face-on maps show that the H I disk is extended to a radius of 15-20 kpc and its outskirts are asymmetric to the Galactic center, while most of the H2 gas is distributed inside the solar circle. The total gas mass within a radius of 30 kpc amounts to 8.0 × 109 M⊙, 89% and 11% of which are H I and H2, respectively. The vertical slices show that the outer H I disk is strongly warped and the inner H I and H2 disks are corrugated. The total gas map is advantageous for tracing spiral structures from the inner to outer disk. Spiral structures such as the Norma-Cygnus, the Perseus, the Sagittarius-Carina, the Scutum-Crux, and the Orion arms are more clearly traced in the total gas map than ever. All the spiral arms are well explained by logarithmic spiral arms with pitch angles of 11°-15°. The molecular fraction of the total gas is high near the Galactic center and decreases with Galactocentric distance. The molecular fraction is also locally enhanced at the spiral arms compared with the inter-arm regions.

DOI： 10.1093/pasj/psv108

arXiv

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

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

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

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

Abstract

We present BISTRO Survey 850 μm dust emission polarization observations of the L1495A-B10 region of the Taurus molecular cloud, taken at the James Clerk Maxwell Telescope (JCMT). We observe a roughly triangular network of dense filaments. We detect nine of the dense starless cores embedded within these filaments in polarization, finding that the plane-of-sky orientation of the core-scale magnetic field lies roughly perpendicular to the filaments in almost all cases. We also find that the large-scale magnetic field orientation measured by Planck is not correlated with any of the core or filament structures, except in the case of the lowest-density core. We propose a scenario for early prestellar evolution that is both an extension to, and consistent with, previous models, introducing an additional evolutionary transitional stage between field-dominated and matter-dominated evolution, observed here for the first time. In this scenario, the cloud collapses first to a sheet-like structure. Uniquely, we appear to be seeing this sheet almost face on. The sheet fragments into filaments, which in turn form cores. However, the material must reach a certain critical density before the evolution changes from being field dominated to being matter dominated. We measure the sheet surface density and the magnetic field strength at that transition for the first time and show consistency with an analytical prediction that had previously gone untested for over 50 yr.

DOI： 10.3847/1538-4357/acbea4

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/acbea4/pdf

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

We present the initial results of our MeerKAT L-band observations of Abell 3376. We achieved higher (5 '') angular resolution and better (similar to 4 mu Jy beam(-1)) sensitivity compared to the previous observations. Our achieved sensitivity is only a factor of 2 larger than the thermal noise of MeerKAT. Astrometric and flux comparison of discrete compact sources in the field between MeerKAT and the Very Large Array (VLA) indicated that our calibration procedures were successful. We detected West and East relics, and radio galaxies, which have been observed in previous works. With minimal missing flux problem in our MeerKAT observations, we derived the spectral indices of the West relic (-1.22 +/- 0.05), East relic (-1.33 +/- 0.08) and central radio galaxies (-0.94 +/- 0.05). The improved images revealed faint, extending radio arcs for relics, and connection between the East relic and radio galaxies. It is probable that (at least some of) the re-accelerated electrons of the East relic are supplied by the jets of the radio galaxies. No significant diffuse radio emission was found in cluster central part, supporting previous works with a much better upper limit of radio flux of <1.8 x 10(23) W Hz(-1).

DOI： 10.1093/pasj/psac009

Web of Science

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

The Perseus arm has a gap in Galactic longitudes (l) between 50° and 80° (hereafter the Perseus arm gap) where the arm has little star formation activity. To better understand the gap, we conducted astrometric observations with VERA (VLBI Exploration of Radio Astrometry) and analyzed archival H i data. We report on parallax and proper motion results from four star-forming regions, of which G050.28-00.39 and G070.33+01.59 are likely associated with the gap. The measured parallaxes are 0.140 ± 0.018 (mas), 0.726 ± 0.038 (mas), 0.074 ± 0.037 (mas), and 0.118 ± 0.035 (mas) for G050.28-00.39, G053.14+00.07, G070.33+01.59, and G079.08+01.33, respectively. Since the fractional parallax error of G070.33+01.59 is large (0.5), we estimated a 3D kinematic distance of the source of 7.7 ± 1.0 kpc using both the LSR velocity (VLSR) and the measured proper motion. Perseus-arm sources G049.41+00.32 and G050.28-00.39 lag relative to a Galactic rotation by 77 ± 17 km s-1 and 31 ± 10 km s-1, respectively. The noncircular motion of G049.41+00.32 cannot be explained by the gravitational potential of the Perseus arm. We discovered rectangular holes with integrated brightness temperatures of <30 K arcdeg in l vs. VLSR of the H i data. One of the holes is centered near (l, VLSR) = (47°, -15 km s-1), and G049.41+00.32 is associated with the rim of the hole. However, G050.28-00.39 is not associated with the hole. We found extended H i emission on one side of the Galactic plane when integrating the H i data over the velocity range covering the hole (i.e., VLSR = [-25, -5] km s-1). G049.41+00.32 and G050.28-00.39 are moving toward the emission. The Galactic H i disk at the same velocity range showed an arc structure, indicating that the disk was pushed from the lower side of the disk. All the observational results might be explained by a cloud collision with the Galactic disk.

DOI： 10.1093/pasj/psab118

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

We present 850 μm polarimetric observations toward the Serpens Main molecular cloud obtained using the POL-2 polarimeter on the James Clerk Maxwell Telescope as part of the B-fields In STar-forming Region Observations survey. These observations probe the magnetic field morphology of the Serpens Main molecular cloud on about 6000 au scales, which consists of cores and six filaments with different physical properties such as density and star formation activity. Using the histogram of relative orientation (HRO) technique, we find that magnetic fields are parallel to filaments in less-dense filamentary structures where NH2<0.93×1022 cm-2 (magnetic fields perpendicular to density gradients), while they are perpendicular to filaments (magnetic fields parallel to density gradients) in dense filamentary structures with star formation activity. Moreover, applying the HRO technique to denser core regions, we find that magnetic field orientations change to become perpendicular to density gradients again at NH2≈4.6×1022 cm-2. This can be interpreted as a signature of core formation. At NH2≈16×1022 cm-2, magnetic fields change back to being parallel to density gradients once again, which can be understood to be due to magnetic fields being dragged in by infalling material. In addition, we estimate the magnetic field strengths of the filaments (B POS = 60-300 μG)) using the Davis-Chandrasekhar-Fermi method and discuss whether the filaments are gravitationally unstable based on magnetic field and turbulence energy densities.

DOI： 10.3847/1538-4357/ac4bbe

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

We conducted observations and analyses of the molecular cloud, N4, which is located at similar to 40 pc from SS 433 and the same line of sight as that of the radio shell, in (CO)-C-12(J = 1-0), (CO)-C-12(J = 3-2), (CO)-C-13(J = 3-2), and grand-state OH emissions. N4 has a strong gradient of the integrated intensity of (CO)-C-12(J = 1-0, 3-2) emission at the northern, eastern, and western edges. The main body of N4 also has a velocity gradient of similar to 0.16 km s(-1) (20")(-1). A velocity shift by up to 3 km s(-1) from the systemic velocity at similar to 49 km s(-1) is detected at only the northwestern part of N4. The volume density of the molecular hydrogen gas and the kinematic temperature are estimated at eight local peaks of (CO)-C-12(J = 1-0) and (CO)-C-13(J = 3-2) emissions by the RADEX code. The calculated n((H2)) is an order of 10(3) cm(-3), and T-k ranges from similar to 20 to similar to 56 K. The mass of N4 is estimated to be similar to 7300 M-circle dot. The thermal and turbulent pressures in N4 are estimated to be similar to 10(5) K cm(-3) and similar to 10(7) K cm(-3), respectively. The relation of the thermal and turbulent pressures in N4 tends to be similar to that of the molecular clouds in the Galactic plane. However, these values are higher than those in the typical molecular clouds in the Galactic plane. Several pieces of circumstantial evidence representing the physical properties of N4 and comparison with the data of infrared and X-ray radiation suggest that N4 is interacting with a jet from SS 433. However, no gamma-ray radiation is detected toward N4. Compared to the previous study, it is hard to detect the gamma-ray radiation by cosmic-ray proton origin due to the low sensitivity of the current gamma-ray observatories. No OH emission was detected toward N4 due to the low sensitivity of the observation and antenna beam dilution.

DOI： 10.1093/pasj/psac012

Web of Science

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Publisher：Astrophysical Journal Letters  

DOI： 10.3847/2041-8213/abeb1c

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Publisher：Astronomy and Astrophysics  

DOI： 10.1051/0004-6361/202038624

Scopus

Publisher：Astrophysical Journal  

DOI： 10.3847/1538-4357/abd0fc

Scopus

Publisher：Astrophysical Journal  

DOI： 10.3847/1538-4357/aba1e2

Scopus

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

We present the first astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the astrometry results from VERA, providing accurate trigonometric-annual-parallax and proper-motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported, while the rest of the 78 sources are referred to in previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry is revisited and compared with that from the other VLBI astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould's Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameters of R0 = 7.92 ± 0.16stat. ± 0.3sys. kpc and Ω☉ = 30.17 ± 0.27stat. ± 0.3sys. km s−1 kpc−1, where R0 and Ω☉ are the distance from the Sun to the Galactic center and the Sun's angular velocity of the Galactic circular rotation, respectively.

DOI： 10.1093/pasj/psaa018

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

DOI： 10.1093/pasj/psz0101

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

We report on measurements of parallax and proper motion for four 22 GHz water maser sources as part of the VERA Outer Rotation Curve project. All the sources show Galactic latitudes of >2◦ and Galactocentric distances of >11 kpc at the Galactic longitude range of 95◦ < l < 126◦. The sources trace the Galactic warp reaching to 200-400 pc, and also the signature of the warp to 600 pc toward the north Galactic pole. The new results, along with previous results in the literature, show that the maximum height of the Galactic warp increases with Galactocentric distance. Also, we examined velocities perpendicular to the disk for the sample, and found oscillatory behavior between the vertical velocities and Galactic heights. This behavior suggests the existence of bending (vertical density) waves, possibly induced by a perturbing satellite (e.g., the passage of the Sagittarius dwarf galaxy).

DOI： 10.1093/pasj/psz125

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

The <SUP>12</SUP>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<SUB>b</SUB> at 1 kpc resolution, with a maximum at a radius of R/a<SUB>b</SUB> ≈ 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<SUB>CR</SUB> and bar pattern speed Ω<SUB>b</SUB> 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<SUB>b</SUB> vs. a<SUB>b</SUB> and Ω<SUB>b</SUB> vs. total stellar mass M<SUB>*</SUB>, 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

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Publications of the Astronomical Society of Japan  

DOI： 10.1093/pasj/psz015

Scopus

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

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Publications of the Astronomical Society of Japan  

DOI： 10.1093/pasj/psz115

Scopus

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

We present the POL-2 850 μm linear polarization map of the Barnard 1 clump in the Perseus molecular cloud complex from the B-fields In STar-forming Region Observations survey at the James Clerk Maxwell Telescope. We find a trend of decreasing polarization fraction as a function of total intensity, which we link to depolarization effects toward higher-density regions of the cloud. We then use the polarization data at 850 μm to infer the plane-of-sky orientation of the large-scale magnetic field in Barnard 1. This magnetic field runs north-south across most of the cloud, with the exception of B1-c, where it turns more east-west. From the dispersion of polarization angles, we calculate a turbulence correlation length of 5.0 ±2.″5 (1500 au) and a turbulent-to-total magnetic energy ratio of 0.5 ±0.3 inside the cloud. We combine this turbulent-to-total magnetic energy ratio with observations of NH3 molecular lines from the Green Bank Ammonia Survey to estimate the strength of the plane-of-sky component of the magnetic field through the Davis-Chandrasekhar-Fermi method. With a plane-of-sky amplitude of 120 ±60 μG and a criticality criterion λ c = 3.0 ±1.5, we find that Barnard 1 is a supercritical molecular cloud with a magnetic field nearly dominated by its turbulent component.

DOI： 10.3847/1538-4357/ab1b23

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Publisher：Astrophysical Journal  

DOI： 10.3847/1538-4357/ab0958

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

We present the 850 μm polarization observations toward the IC 5146 filamentary cloud taken using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) and its associated polarimeter (POL-2), mounted on the James Clerk Maxwell Telescope, as part of the B-fields In STar forming Regions Observations. This work is aimed at revealing the magnetic field morphology within a core-scale (≲1.0 pc) hub-filament structure (HFS) located at the end of a parsec-scale filament. To investigate whether the observed polarization traces the magnetic field in the HFS, we analyze the dependence between the observed polarization fraction and total intensity using a Bayesian approach with the polarization fraction described by the Rice likelihood function, which can correctly describe the probability density function of the observed polarization fraction for low signal-to-noise ratio data. We find a power-law dependence between the polarization fraction and total intensity with an index of 0.56 in A V ∼ 20-300 mag regions, suggesting that the dust grains in these dense regions can still be aligned with magnetic fields in the IC 5146 regions. Our polarization maps reveal a curved magnetic field, possibly dragged by the contraction along the parsec-scale filament. We further obtain a magnetic field strength of 0.5 ±; 0.2 mG toward the central hub using the Davis-Chandrasekhar-Fermi method, corresponding to a mass-to-flux criticality of ∼1.3 ±; 0.4 and an Alfvénic Mach number of <0.6. These results suggest that gravity and magnetic field are currently of comparable importance in the HFS and that turbulence is less important.

DOI： 10.3847/1538-4357/ab13a2

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

We studied large-scale magnetic field reversals of a galaxy based on a magnetic vector map of NGC6946. The magnetic vector map was constructed based on the polarization maps in the C and X bands after the determination of the geometrical orientation of a disk with the use of an infrared image and the velocity field, according to the trailing spiral arm assumption. We examined the azimuthal variation of the magnetic vector and found that the magnetic pitch angle changes continually as a function of the azimuthal angle in the inter-arm region. However, the direction of the magnetic field had 180° jumps at the azimuthal angles of 20°, 110°, 140°, 220°, 280°, and 330°. These reversals seem to be related to the spiral arms since the locations of the jumps are coincident with those of the spiral arms. These six reversals of the magnetic field were seen only in the inner region of NGC6946 whereas four reversals can be identified in the outer region.

DOI： 10.3390/galaxies7020059

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

A correlation analysis is obtained among Faraday rotation measure, H i column density, and thermal and synchrotron radio brightness using archival all-sky maps of the Galaxy. A method is presented to calculate the magnetic strength and its line-of-sight (LOS) component, volume gas densities, effective LOS depth, and effective scale height of the disc from these data in a hybrid way. Applying the method to archival data, all-sky maps of the local magnetic field strength and its parallel component are obtained, which reveal details of local field orientation.

DOI： 10.1093/mnras/stz407

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

Observational study of galactic magnetic fields is limited by projected observables. Comparison with numerical simulations is helpful to understand the real structures, and observational visualization of numerical data is an important task.Machida et al. (2018) have reported Faraday depth maps obtained from numerical simulations. They showed that the relation between azimuthal angle and Faraday depth depends on the inclination angle. In this paper, we investigate 100MHz to 10 GHz radio synchrotron emission from spiral galaxies, using the data of global three-dimensional magnetohydrodynamic simulations. We model internal and external Faraday depolarization at small scales and assume a frequency-independent depolarization. It is found that the internal and external Faraday depolarization becomes comparable inside the disc and the dispersion of Faraday depth becomes about 4 radm-2 for face-on view and 40 radm-2 for edge-on view, respectively. The internal depolarization becomes ineffective in the halo. Because of the magnetic turbulence inside the disc, frequency-independent depolarization works well and the polarization degree becomes 0.3 at high frequency. When the observed frequency is in the 100 MHz band, polarized intensity vanishes in the disc, while that from the halo can be observed. Because the remaining component of polarized intensity is weak in the halo and the polarization degree is about a few per cent, it may be difficult to observe that component. These results indicate that the structures of global magnetic fields in spiral galaxies could be elucidated, if broad-band polarimetry such as that with the Square Kilometre Array is achieved.

DOI： 10.1093/mnras/sty2940

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

Magnetic fields in the universe play an essential role in observations of the radio synchrotron continuum; however, we do not know enough about them, either observationally or theoretically. We are interested in galactic magnetic fields because they affect the structural formation of galaxies in terms of star-forming regions, spiral arms, and threads at the galactic center. To clarify the importance of magnetic fields, we carried out numerical simulations of the galactic gaseous disk with magnetic fields. We also calculated observables, such as the rotation measure and Stokes parameters, from the results of numerical simulation. FD maps and intensity maps have been reported, and the relation between azimuthal angle and FD has been shown to depend on the inclination of the observer. Furthermore, it has been shown that a polarized intensity below 800 MHz reflects field structure in the halo region, although the intensity is weak. The present paper summarizes the effects of Faraday depolarization and the relation between magnetic-field structure and Stokes parameters.

DOI： 10.3390/galaxies7010015

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

As part our investigation into the Galactic rotation curve, we carried out Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion. The annual parallax was measured to be 0.151 ± 0.042 mas, which corresponds to a distance of D = 6.61+–215544 kpc, and the obtained proper motion components were (μαcosδ, μδ) = (–1.44 ± 0.15, –0.27 ± 0.16) mas yr–1 in equatorial coordinates. Assuming Galactic constants of (R00) = (8.05 ± 0.45 kpc, 238 ± 14 km s–1), the Galactocentric distance and rotation velocity were measured to be (R, ) = (13.04 ± 2.24 kpc, 239 ± 22 km s–1), which are consistent with a flat Galactic rotation curve. The newly estimated distance provides a more accurate bolometric luminosity of the central young stellar object, LBol = (3.11 ± 2.86) × 103 L, which corresponds to a spectral type of B1–B2. Analysis of 12CO (J = 1–0) survey data obtained with the Five College Radio Astronomical Observatory (FCRAO) 14 m telescope shows that the molecular cloud associated with IRAS 01123+6430 consists of arc-like and linear components, which matches well a structure predicted by numerical simulation of the cloud–cloud collision phenomenon. The coexistence of arc-like and linear components implies that the relative velocity of the two initial clouds was as slow as 3–5 km s–1, which meets the expected criteria of massive star formation where the core mass is effectively increased in the presence of low relative velocity (∼3–5 km s–1), as suggested by Takahira, Tasker, and Habe (2014, ApJ, 792, 63).

DOI： 10.1093/pasj/psz101

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A jet termination region provides us with useful information about how a jet interacts with the interstellar medium. Identifying the strength and orientation of magnetic fields at the terminal is crucially important to understanding the mechanism of cosmic-ray acceleration. In this article, we report results of our Faraday-tomography analysis of the eastern region of the radio nebula W50, where a jet from the microquasar SS433 seems to terminate. We apply QU-fitting, a method of Faraday-tomography, to data from the Australia Telescope Compact Array (ATCA) at 1.3-3.0 GHz. In the analysis, we distinguish multiple polarized sources along the line of sight. We identify Galactic emission candidates at Faraday depths around 0 rad m-2 and 300 rad m-2. The Galactic emission around 0 rad m-2 is possibly located in front of W50. We also find emission from W50 with Faraday depths between ϕ = -112 to 228 rad m-2.

DOI： 10.3390/galaxies6040137

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

Observational study of galactic magnetic fields is hampered by the fact that the observables only probe various projections of the magnetic fields. Comparison with numerical simulations is helpful to understand the real structures, and observational visualization of numerical data is an important task. In this paper, we investigate 8 GHz radio synchrotron emission from spiral galaxies, using the data of global three-dimensional magnetohydrodynamic simulations. We assume a frequency independent depolarization in our observational visualization. We find that the appearance of the global magnetic field depends on the viewing angle: a face-on view seemingly has hybrid magnetic field types combining axisymmetric modes with higher order modes; at a viewing angle of ~70°, the galaxy seems to contain a ring-like magnetic field structure; while in edge-on view, only field structure parallel to the disc can be seen. The magnetic vector seen at 8 GHz traces the global magnetic field inside the disc. These results indicate that the topology of global magnetic field obtained from the relation between azimuthal angle and Faraday depth strongly depends on the viewing angle of the galaxy. As one of the examples, we compare our results at a viewing angle of 25° with the results of IC342. The relation between azimuthal angle and Faraday depth of the numerical result shows a tendency similar to IC342, such as the peak values of the Faraday depth.

DOI： 10.1093/mnras/sty1799

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

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

We present the results of dust emission polarization measurements of Ophiuchus-B (Oph-B) carried out using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera with its associated polarimeter (POL-2) on the James Clerk Maxwell Telescope in Hawaii. This work is part of the B-fields in Star-forming Region Observations survey initiated to understand the role of magnetic fields in star formation for nearby star-forming molecular clouds. We present a first look at the geometry and strength of magnetic fields in Oph-B. The field geometry is traced over ∼0.2 pc, with clear detection of both of the sub-clumps of Oph-B. The field pattern appears significantly disordered in sub-clump Oph-B1. The field geometry in Oph-B2 is more ordered, with a tendency to be along the major axis of the clump, parallel to the filamentary structure within which it lies. The degree of polarization decreases systematically toward the dense core material in the two sub-clumps. The field lines in the lower density material along the periphery are smoothly joined to the large-scale magnetic fields probed by NIR polarization observations. We estimated a magnetic field strength of 630 ± 410 μG in the Oph-B2 sub-clump using a Davis-Chandrasekhar-Fermi analysis. With this magnetic field strength, we find a mass-to-flux ratio λ = 1.6 ± 1.1, which suggests that the Oph-B2 clump is slightly magnetically supercritical.

DOI： 10.3847/1538-4357/aac4a6

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

We report the Australia Telescope Compact Array 16 cm observation of CIZA J1358.9-4750. Recent X-ray studies imply that this galaxy cluster is composed of merging, binary clusters. Using the EW367 configuration, we found no significant diffuse radio emission in and around the cluster. An upper limit of the total radio power at 1.4 GHz is ∼1.1 × 1022 W Hz-1 in 30 square arcminutes, which is a typical size for radio relics. It is known that an empirical relation holds between the total radio power and X-ray luminosity of the host cluster. The upper limit is about one order of magnitude lower than the power expected from the relation. Very young (∼70 Myr) shocks with low Mach numbers (∼1.3), which are often seen at an early stage of merger simulations, are suggested by the previous X-ray observation. The shocks may generate cosmic-ray electrons with a steep energy spectrum, which is consistent with non-detection of bright (>1023 W Hz-1) relic in this 16 cm band observation. Based on the assumption of energy equipartition, the upper limit gives a magnetic field strength of below 0.68f(Dlos/1 Mpc)-1(γmin/200)-1 μG, where f is the cosmic-ray total energy density over the cosmic-ray electron energy density, Dlos is the depth of the shock wave along the sightline, and min is the lower cutoff Lorentz factor of the cosmic-ray electron energy spectrum.

DOI： 10.1093/pasj/psy042

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

We present 850 μm imaging polarimetry data of the ρ Oph-A core taken with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its polarimeter (POL-2) as part of our ongoing survey project, -fields In STar forming RegiOns (BISTRO). The polarization vectors are used to identify the orientation of the magnetic field projected on the plane of the sky at a resolution of 0.01 pc. We identify 10 subregions with distinct polarization fractions and angles in the 0.2 pc ρ Oph-A core; some of them can be part of a coherent magnetic field structure in the ρ Oph region. The results are consistent with previous observations of the brightest regions of ρ Oph-A, where the degrees of polarization are at a level of a few percent, but our data reveal for the first time the magnetic field structures in the fainter regions surrounding the core where the degree of polarization is much higher (>5%). A comparison with previous near-infrared polarimetric data shows that there are several magnetic field components that are consistent at near-infrared and submillimeter wavelengths. Using the Davis-Chandrasekhar-Fermi method, we also derive magnetic field strengths in several subcore regions, which range from approximately 0.2 to 5 mG. We also find a correlation between the magnetic field orientations projected on the sky and the core centroid velocity components.

DOI： 10.3847/1538-4357/aabd82

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

We report a polarization analysis of the eastern region of W 50, observed with the Australia Telescope Compact Array (ATCA) at 1.4-3.0 GHz. In order to study the physical structures in the region where the SS 433 jet and W 50 interact, we obtain an intrinsic magnetic field vector map of that region. We find that the orientation of the intrinsic magnetic field vectors are aligned along the total intensity structures, and that there are characteristic, separate structures related to the jet, the bow shock, and the terminal shock. The Faraday rotation measures (RMs), and the results of Faraday tomography suggest that a high-intensity, filamentary structure in the north-south direction of the eastern-edge region can be separated into at least two parts to the north and south. The results of Faraday tomography also show that there are multiple components along the line of sight and/or within the beam area. In addition, we analyze the X-ray ring-like structure observed with XMM-Newton. While the possibility still remains that this X-ray ring is “real”, it seems that the structure is not ring-like at radio wavelengths. Finally, we suggest that the structure is a part of the helical structure that coils the eastern ear of W 50.

DOI： 10.1093/pasj/psy003

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

The magnetic field is ubiquitous in the universe. Though it plays an essential role in various astrophysical phenomena, its real origin and evolution are poorly known. This article reviews the understanding of the latest research concerning magnetic fields in the interstellarmedium, the Milky Way Galaxy, external galaxies, active galactic nuclei, clusters of galaxies, and the cosmic web. Particularly, the review is concentrated in the achievements that have been provided by centimeter- and meter-wavelength radio observations. The article also introduces various methods for analyzing linear polarization data, including synchrotron radiation, Faraday rotation, depolarization, and Faraday tomography.

DOI： 10.1093/pasj/psx123

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Publications of the Astronomical Society of Japan  

DOI： 10.1093/pasj/psx061

Scopus

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

We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array 2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey's aims and objectives. We describe the rationale behind the survey, and the questions that the survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC 1 region. We see that the magnetic field lies approximately perpendicular to the famous "integral filament" in the densest regions of that filament. Furthermore, we see an "hourglass" magnetic field morphology extending beyond the densest region of the integral filament into the less-dense surrounding material, and discuss possible causes for this. We also discuss the more complex morphology seen along the Orion Bar region. We examine the morphology of the field along the lower-density northeastern filament. We find consistency with previous theoretical models that predict magnetic fields lying parallel to low-density, non-self-gravitating filaments, and perpendicular to higher-density, self-gravitating filaments.

DOI： 10.3847/1538-4357/aa70a0

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

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

DOI： 10.1093/pasj/psx019

Scopus

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

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

The Schmidt law (SF law) in the Milky Way was investigated using 3D distribution maps of H II regions and HI and molecular (H-2) gases with spatial resolutions of similar to 1 kpc in the Galactic plane and a few tens of pc in the vertical direction. H II regions were shown to be distributed in a star-forming (SF) disk with nearly constant vertical full thickness 92 pc in spatial coincidence with the molecular gas disk. The vertically averaged volume star formation rate (SFR) rho(SFR) in the SF disk is related to the surface SFR Sigma(SFR) by rho(SFR)/[M-circle dot yr(-1) kpc(-3)] = 9.26 x Sigma(SFR)/[M-circle dot yr(-1) kpc(-2)]. The SF law fitted by a single power law of gas density in the form of Sigma(SFR) alpha rho SFR alpha rho(alpha)(gas) and alpha Sigma(beta)(gas) showed indices of alpha = 0.78 +/- 0.05 for rho H-2 and 2.15 +/- 0.08 for rho(total), and beta = 1.14 +/- 0.23 for Sigma(total), where rho and Sigma denote volume and surface densities, respectively. The star formation rate is shown to be directly related to the molecular gas, but indirectly to HI and total gas densities. The dependence of the SF law on the gaseous phase is explained by the phase transition theory between HI and H-2.

DOI： 10.1093/pasj/psw123

Web of Science

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

We report on the measurement of the trigonometric parallaxes of 1612 MHz hydroxyl masers around two asymptotic giant branch stars, WX Psc and OH 138.0+7.2, using the NRAO Very Long Baseline Array with in-beam phase referencing calibration. We obtain a 3σ upper limit of ≤5.3 mas on the parallax of WX Psc, corresponding to a lower limit distance estimate of ≳190 pc. The obtained parallax of OH 138.0+7.2 is 0.52 ±0.09 mas (±18%), corresponding to a distance of 1.9-0.3+0.4, making this the first hydroxyl maser parallax below one milliarcsecond. We also introduce a new method of error analysis for detecting systematic errors in the astrometry. Finally, we compare our trigonometric distances to published phase-lag distances toward these stars and find a good agreement between the two methods.

DOI： 10.3847/1538-3881/153/3/119

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

Three-dimensional structure of the Aquila Rift of magnetized neutral gas is investigated by analysing H I and CO line data. The projected distance on the Galactic plane of the H I arch of the Aquila Rift is r(perpendicular to) similar to 250 pc from the Sun. The H I arch emerges at l similar to 30 degrees, reaches to altitudes as high as similar to 500 pc above the plane at l similar to 350 degrees, and returns to the disc at l similar to 270 degrees. The extent of arch at positive latitudes is similar to 1 kpc and the width is similar to 100 pc. The eastern root is associated with the giant molecular cloud complex, which is the main body of the optically defined Aquila Rift. The H I and molecular masses of the Rift are estimated to be M-HI similar to 1.4 x 10(5)M circle dot and M-H2 similar to 3 x 10(5)M circle dot. Gravitational energies to lift the gases to their heights are E-grav:H I similar to 1.4 x 10(51) erg and E-grav:H2 similar to 0.3 x 10(51) erg, respectively. Magnetic field is aligned along the HI arch of the Rift, and the strength is measured to be B similar to 10 mu Gusing Faraday rotation measures of extragalactic radio sources. The magnetic energy is estimated to be E-mag similar to 1.2 x 10(51) erg. A possible mechanism of formation of the Aquila Rift is proposed in terms of interstellar magnetic inflation by a sinusoidal Parker instability of wavelength of similar to 2.5 kpc and amplitude similar to 500 pc.

DOI： 10.1093/mnras/stw2310

Web of Science

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arXiv

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

We present simultaneous mappings of J = 1-0 emission of 12CO, 13CO, and C18O molecules toward the whole disk (8' × 5' or 20.8 kpc × 13.0 kpc) of the nearby barred spiral galaxy NGC 2903 with the Nobeyama Radio Observatory 45 m telescope at an effective angular resolution of 20″ (or 870 pc). We detected 12CO(J = 1-0) emission over the disk of NGC 2903. In addition, significant 13CO(J = 1-0) emission was found at the center and bar-ends, whereas we could not detect any significant C18O(J = 1-0) emission. In order to improve the signal-to-noise ratio of CO emission and to obtain accurate line ratios of 12CO(J = 2-1)/12CO(J = 1-0) (R2-1/1-0) and 13CO(J = 1-0)/12CO(J = 1-0) (R13/12), we performed the stacking analysis for our 12CO(J = 1-0), 13CO(J = 1-0), and archival 12CO(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 R13/12 with high significance for all the regions. We found that both R2-1/1-0 and R13/12 differ according to the regions, which reflects the difference in the physical properties of molecular gas, i.e., density (n_H_2) and kinetic temperature (TK). We determined n_H_2 and TK using R2-1/1-0 and R13/12 based on the large velocity gradient approximation. The derived n_H_2 ranges from ˜1000 cm-3 (in the bar, bar-ends, and spiral arms) to 3700 cm-3 (at the center) and the derived TK 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_H_2 and TK, and found a positive correlation between SFE and n_H_2 with correlation coefficient for the least-squares power-law fit R2 of 0.50. This suggests that molecular gas density governs the spatial variations in SFEs.

DOI： 10.1093/pasj/psw080

arXiv

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

DOI： 10.1051/0004-6361/201629178

arXiv

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

Three-dimensional (3D) distribution of the volume-density molecular fraction, defined by f_mol^ρ =ρ _H_2/(ρ _{H I}+ρ _H_2), is studied in the Milky Way Galaxy. The molecular front appears at galacto-centric distance of R ˜ 8 kpc, where the galactic-scale phase transition from atomic to molecular hydrogen occurs with f_mol^ρ dropping from ˜0.8 to 0.2 within a radial interval as narrow as ˜0.5 kpc. The f_mol^ρ front is much sharper than that of the surface density molecular fraction. The f_mol^ρ front also appears in the direction vertical to the galactic plane with a full width of the high-f_mol^ρ disk to be ˜100 pc. The radial and vertical f_mol^ρ profiles, particularly the front behavior, are fitted by theoretical curves calculated using the observed density profile and assumed radiation field and metallicity with exponential gradients. The molecular fraction was found to be enhanced along spiral arms at radii R ˜ 6 to 10 kpc, such as the Perseus arm. This implies that the molecular clouds are produced from H I in the arms and are dissociated in the interarm regions in the transition region around the molecular front. We also show that there is a threshold value of mean H I density, over which H I is transformed into molecular gas.

DOI： 10.1093/pasj/psw062

arXiv

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

DOI： 10.1093/pasj/psv082

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