arXiv subjects

Junya Nishi

Publications and source records attributed to Junya Nishi.

6 recordsLinked to original sources

arXiv2026

Gas Kinematics and Cosmic-Ray Acceleration in the Gamma-ray SNRs W41 and G22.7-0.2

We present a study of the interstellar medium associated with the two middle-aged supernova remnants (SNRs) W41 and G22.7-0.2, both detected in TeV gamma-rays. Using high-angular-resolution $^{12}$CO($J$ = 1-0) data from the Nobeyama 45-m telescope and HI data from the VLA, we investigated the spatial and kinematic properties of molecular and atomic gas that interact with the SNRs. We identified associated clouds in the velocity ranges of +50-+80 km s$^{-1}$ for W41 and +76-+110 km s$^{-1}$ for G22.7-0.2. Column density analysis indicates that target protons are dominated by molecular hydrogen, while atomic hydrogen contributes less than $\sim$10-15% even after correction for self-absorption. The mean proton densities are $\sim$1.2$\times$10$^{3}$ cm$^{-3}$ for W41 and $\sim$5.3$\times$10$^{2}$ cm$^{-3}$ for G22.7-0.2. From the gamma-ray luminosities, we estimate the total energy of accelerated cosmic-ray protons as $W_\mathrm{p}$ $\sim$3$\times$10$^{47}$~erg for W41 and $\sim$1$\times$10$^{48}$ erg for G22.7-0.2, corresponding to 0.03-0.1% of the canonical supernova explosion energy. hese $W_\mathrm{p}$ values agree with the decreasing trend in $W_\mathrm{p}$ observed in the middle-aged SNRs within the previously reported SNR age-$W_\mathrm{p}$ relation.

astro-ph.HE↗

arXiv2024

KAgoshima Galactic Object survey with Nobeyama 45-metre telescope by Mapping in Ammonia lines (KAGONMA): Discovery of parsec-scale CO depletion in the Canis Major star-forming region

In observational studies of infrared dark clouds, the number of detections of CO freeze-out onto dust grains (CO depletion) at pc-scale is extremely limited, and the conditions for its occurrence are, therefore, still unknown. We report a new object where pc-scale CO depletion is expected. As a part of Kagoshima Galactic Object survey with Nobeyama 45-m telescope by Mapping in Ammonia lines (KAGONMA), we have made mapping observations of NH3 inversion transition lines towards the star-forming region associated with the CMa OB1 including IRAS 07077-1026, IRAS 07081-1028, and PGCC G224.28-0.82. By comparing the spatial distributions of the NH3 (1,1) and C18O (J=1-0), an intensity anti-correlation was found in IRAS 07077-1026 and IRAS 07081-1028 on the ~1 pc scale. Furthermore, we obtained a lower abundance of C18O at least in IRAS 07077-1026 than in the other parts of the star-forming region. After examining high density gas dissipation, photodissociation, and CO depletion, we concluded that the intensity anti-correlation in IRAS 07077-1026 is due to CO depletion. On the other hand, in the vicinity of the centre of PGCC G224.28-0.82, the emission line intensities of both the NH3 (1,1) and C18O (J=1-0) were strongly detected, although the gas temperature and density were similar to IRAS 07077-1026. This indicates that there are situations where C18O (J=1-0) cannot trace dense gas on the pc scale and implies that the conditional differences that C18O (J=1-0) can and cannot trace dense gas are unclear.

astro-ph.GA↗

arXiv2024

Sub-kpc scale gas density histogram of the Galactic molecular gas: a new statistical method to characterise galactic-scale gas structures

To understand physical properties of the interstellar medium (ISM) on various scales, we investigate it at parsec resolution on the kiloparsec scale. Here, we report on the sub-kpc scale Gas Density Histogram (GDH) of the Milky Way. The GDH is a density probability distribution function (PDF) of the gas volume density. Using this method, we are free from an identification of individual molecular clouds and their spatial structures. We use survey data of $^{12}$CO and $^{13}$CO ($J$=1-0) emission in the Galactic plane ($l = 10^{\circ}$-$50^{\circ}$) obtained as a part of the FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45m telescope (FUGIN). We make a GDH for every channel map of $2^{\circ} \times 2^{\circ}$ area, including the blank sky component, and without setting cloud boundaries. This is a different approach from previous works for molecular clouds. The GDH fits well to a single or double log-normal distribution, which we name the low-density log-normal (L-LN) and high-density log-normal (H-LN) components, respectively. The multi-log-normal components suggest that the L-LN and H-LN components originate from two different stages of structure formation in the ISM. Moreover, we find that both the volume ratios of H-LN components to total ($f_{\mathrm{H}}$) and the width of the L-LN along the gas density axis ($σ_{\rm{L}}$) show coherent structure in the Galactic-plane longitude-velocity diagram. It is possible that these GDH parameters are related to strong galactic shocks and other weak shocks in the Milky Way.

astro-ph.GA↗

arXiv2023

Multi log-normal density structure in Cygnus-X molecular clouds: A fitting for N-PDF without power-law

We studied the H$_2$ column density probability distribution function (N-PDF) based on molecular emission lines using the Nobeyama 45-m Cygnus X CO survey data. Using the DENDROGRAM and SCIMES algorithms, we identified 124 molecular clouds in the $^{13}$CO data. From these identified molecular clouds, an N-PDF was constructed for 11 molecular clouds with an extent of more than 0.4 deg$^2$. From the fitting of the N-PDF, we found that the N-PDF could be well-fitted with one or two log-normal distributions. These fitting results provided an alternative density structure for molecular clouds from a conventional picture. We investigated the column density, dense molecular cloud cores, and radio continuum source distributions in each cloud and found that the N-PDF shape was less correlated with the star-forming activity over a whole cloud. Furthermore, we found that the log-normal N-PDF parameters obtained from the fitting showed two impressive features. First, the log-normal distribution at the low-density part had the same mean column density ($\sim$ 10$^{21.5}$ cm$^{-2}$) for almost all the molecular clouds. Second, the width of the log-normal distribution tended to decrease with an increasing mean density of the structures. These correlations suggest that the shape of the N-PDF reflects the relationship between the density and turbulent structure of the whole molecular cloud but is less affected by star-forming activities.

astro-ph.GA↗

arXiv2021

KAgoshima Galactic Object survey with Nobeyama 45-metre telescope by Mapping in Ammonia lines (KAGONMA): Star formation feedback on dense molecular gas in the W33 complex

We present the results of NH3 (1,1), (2,2) and (3,3) and H2O maser simultaneous mapping observations toward the high-mass star-forming region W33 with the Nobeyama 45-m radio telescope. W33 has six dust clumps and one of which, W33 Main, is associated with a compact HII region. To investigate star-forming feedback activity on its surroundings, the spatial distribution of the physical parameters was established. The distribution of the rotational temperature shows a systematic change from west to east in our observed region. The high-temperature region obtained in the region near W33 Main is consistent with interaction between the compact HII region and the periphery molecular gas. The size of the interaction area is estimated to be approximately 1.25 pc. NH3 absorption features are detected toward the centre of the HII region. Interestingly, the absorption feature was detected only in the NH3 (1,1) and (2,2) transitions, with no absorption feature seen in the (3,3) transition. These complex profiles in NH3 are difficult to explain by a simple model and may suggest that the gas distribution around the HII region is highly complicated.

astro-ph.GA↗

arXiv2020

The First VERA Astrometry Catalog

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 78 sources are referred to previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry are revisited and compared with those 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 parameter of $R_{0}=7.92\pm0.16_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~kpc and $Ω_{\odot}=30.17\pm0.27_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~km~s$^{-1}$~kpc$^{-1}$, where $R_{0}$ and $Ω_{\odot}$ are the distance from the Sun to the Galactic center and the Sun's angular velocity of the Galactic circular rotation, respectively.

astro-ph.GA↗