The second survey of the molecular clouds in the Large Magellanic Cloud in super(12)CO was carried out by NANTEN. The sensitivity of this survey is twice as high as that of the previous NANTEN ...survey, leading to a detection of molecular clouds with image M sub(image). We identified 272 molecular clouds, 230 of which are detected at three or more observed positions. We derived the physical properties, such as size, line width, and virial mass, of the 164 GMCs that have an extent more than the beam size of NANTEN in both the major and minor axes. The CO luminosity and virial mass of the clouds show a good correlation of image, with a Spearman rank correlation of 0.8, suggesting that the clouds are in nearly virial equilibrium. Assuming the clouds are in virial equilibrium, we derived an X sub(CO)-factor of image cm super(-2) (K km s super(-1)) super(-1). The mass spectrum of the clouds is fitted well by a power law of image above the completeness limit of image M sub(image). The slope of the mass spectrum becomes steeper if we fit only the massive clouds, e.g., image for image M sub(image).
N103B is a Type Ia supernova remnant (SNR) in the Large Magellanic Cloud (LMC). We carried out new 12CO(J = 3-2) and 12CO(J = 1-0) observations using ASTE and ALMA. We have confirmed the existence of ...a giant molecular cloud at VLSR ∼ 245 km s−1 toward the southeast of the SNR using ASTE 12CO(J = 3-2) data at an angular resolution of ∼25″ (∼6 pc in the LMC). Using the ALMA 12CO(J = 1-0) data, we have spatially resolved CO clouds along the southeastern edge of the SNR with an angular resolution of ∼1 8 (∼0.4 pc in the LMC). The molecular clouds show an expanding gas motion in the position-velocity diagram with an expansion velocity of ∼5 km s−1. The spatial extent of the expanding shell is roughly similar to that of the SNR. We also find tiny molecular clumps in the directions of optical nebula knots. We present a possible scenario that N103B exploded in the wind-bubble formed by the accretion winds from the progenitor system, and is now interacting with the dense gas wall. This is consistent with a single-degenerate scenario.
We carried out 12CO(J = 1-0) observations of the Galactic gamma-ray supernova remnant (SNR) Kesteven 79 using the Nobeyama Radio Observatory 45 m radio telescope, which has an angular resolution of ...∼20 arcsec. We identified molecular and atomic gas interacting with Kesteven 79, whose radial velocity is ∼80 km s−1. The interacting molecular and atomic gases show good spatial correspondence with the X-ray and radio shells, which have an expanding motion with an expanding velocity of ∼4 km s−1. The molecular gas associated with the radio and X-ray peaks also exhibits a high intensity ratio of CO 3-2/1-0 > 0.8, suggesting a kinematic temperature of ∼24 K, owing to heating by the supernova shock. We determined the kinematic distance to the SNR to be ∼5.5 kpc and the radius of the SNR to be ∼8 pc. The average interstellar proton density inside of the SNR is ∼360 cm−3, of which atomic protons comprise only ∼10%. Assuming a hadronic origin for the gamma-ray emission, the total cosmic-ray proton energy above 1 GeV is estimated to be ∼5 × 1048 erg.
This paper presents a survey of microwave front-end receivers installed at radio telescopes throughout the world. This unprecedented analysis was conducted as part of a review of front-end ...developments for Italian radio telescopes, initiated by the Italian National Institute for Astrophysics in 2016. Fifteen international radio telescopes have been selected to be representative of the instrumentation used for radio astronomical observations in the frequency domain from 300 MHz to 116 GHz. A comprehensive description of the existing receivers is presented and their characteristics are compared and discussed. The observing performances of the complete receiving chains are also presented. An overview of ongoing developments illustrates and anticipates future trends in front-end projects to meet the most ambitious scientific research goals.
Furukawa et al. reported the existence of a large mass of molecular gas associated with the super star cluster Westerlund 2 and the surrounding H II region RCW49, based on a strong morphological ...correspondence between NANTEN2 {sup 12}CO(J = 2-1) emission and Spitzer IRAC images of the H II region. We here present temperature and density distributions in the associated molecular gas at approx3.5 pc resolution, as derived from a large velocity gradient analysis of the {sup 12}CO(J = 2-1), {sup 12}CO(J = 1-0), and {sup 13}CO(J = 2-1) transitions. The kinetic temperature is as high as approx60-150 K within a projected distance of approx5-10 pc from Westerlund 2 and decreases to as low as approx10 K away from the cluster. The high temperature provides robust verification that the molecular gas is indeed physically associated with the H II region, supporting Furukawa et al.'s conclusion. The derived temperature is also roughly consistent with theoretical calculations of photodissociation regions (PDRs), while the low spatial resolution of the present study does not warrant a more detailed comparison with PDR models. We suggest that the molecular clouds presented here will serve as an ideal laboratory to test theories on PDRs in future higher resolution studies.
RX J0046.5−7308 is a shell-type supernova remnant (SNR) in the Small Magellanic Cloud (SMC). We carried out new 12CO(J = 1-0, 3-2) observations toward the SNR using Mopra and the Atacama ...Submillimeter Telescope Experiment. We found eight molecular clouds (A-H) along the X-ray shell of the SNR. The typical cloud size and mass are ∼10-15 pc and ∼1000-3000 M☉, respectively. The X-ray shell is slightly deformed and has the brightest peak in the southwestern shell where two molecular clouds A and B are located. The four molecular clouds A, B, F, and G have high intensity ratios of 12CO(J = 3-2)/12CO(J = 1-0) > 1.2, which are not attributable to any identified internal infrared sources or high-mass stars. The H i cavity and its expanding motion are found toward the SNR, which are likely created by strong stellar winds from a massive progenitor. We suggest that the molecular clouds A-D, F, and G and H i clouds within the wind-blown cavity at VLSR = 117.1-122.5 km s−1 are associated with the SNR. The X-ray spectroscopy reveals the dynamical age of yr and the progenitor mass of 30 M☉, which is also consistent with the proposed scenario. We determine physical conditions of the giant molecular cloud LIRS 36A using the large velocity gradient analysis with archival data sets of the Atacama Large Millimeter/submillimeter Array; the kinematic temperature is K and the number density of molecular hydrogen is cm−3. The next generation of γ-ray observations will allow us to study the pion-decay γ-rays from the molecular clouds in the SMC SNR.
We carried out new 12CO(J = 1-0, 3-2) observations of a N63A supernova remnant (SNR) from the LMC using the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Submillimeter Telescope ...Experiment. We find three giant molecular clouds toward the northeast, east, and near the center of the SNR. Using the ALMA data, we spatially resolved clumpy molecular clouds embedded within the optical nebulae in both the shock-ionized and photoionized lobes discovered by previous H and S ii observations. The total mass of the molecular clouds is ∼800 M☉ for the shock-ionized region and ∼1700 M☉ for the photoionized region. Spatially resolved X-ray spectroscopy reveals that the absorbing column densities toward the molecular clouds are ∼(1.5-6.0) × 1021 cm−2, which are ∼1.5-15 times less than the averaged interstellar proton column densities for each region. This means that the X-rays are produced not only behind the molecular clouds, but also in front of them. We conclude that the dense molecular clouds have been completely engulfed by the shock waves, but have still survived erosion owing to their high density and short interacting time. The X-ray spectrum toward the gas clumps is well explained by an absorbed power-law model or a high-temperature plasma model, in addition to thermal plasma components, implying that the shock-cloud interaction is efficiently working for both cases through the shock ionization and magnetic field amplification. If the hadronic gamma-ray is dominant in the GeV band, the total energy of the cosmic-ray protons is calculated to be ∼(0.3-1.4) × 1049 erg, with an estimated interstellar proton density of ∼190 90 cm−3, containing both the shock-ionized gas and neutral atomic hydrogen.
ABSTRACT We present Spitzer/IRS mid-infrared spectral maps of the Galactic star-forming region M17 as well as IRSF/SIRIUS Brγ and Nobeyama 45 m/FOREST 13CO (J = 1-0) maps. The spectra show prominent ...features due to polycyclic aromatic hydrocarbons (PAHs) at wavelengths of 6.2, 7.7, 8.6, 11.3, 12.0, 12.7, 13.5, and 14.2 m. We find that the PAH emission features are bright in the region between the H ii region traced by Brγ and the molecular cloud traced by 13CO, supporting that the PAH emission originates mostly from photo-dissociation regions. Based on the spatially resolved Spitzer/IRS maps, we examine spatial variations of the PAH properties in detail. As a result, we find that the interband ratio of PAH 7.7 m/PAH 11.3 m varies locally near M17SW, but rather independently of the distance from the OB stars in M17, suggesting that the degree of PAH ionization is mainly controlled by local conditions rather than the global UV environments determined by the OB stars in M17. We also find that the interband ratios of the PAH 12.0 m, 12.7 m, 13.5 m, and 14.2 m features to the PAH 11.3 m feature are high near the M17 center, which suggests structural changes of PAHs through processing due to intense UV radiation, producing abundant edgy irregular PAHs near the M17 center.
We have performed very long baseline interferometry (VLBI) and single-dish monitoring of 22-GHz H2O maser emission from the high-mass young stellar object G353.273+0.641 with the VLBI Exploration of ...Radio Astrometry (VERA) and the Tomakamai 11-m radio telescope. Two maser flares have been detected, separated by almost two years. Frequent VLBI monitoring has revealed that the flare activity has been accompanied by structural change of the prominent shock front traced by H2O maser alignments. We have detected only blueshifted emission and all maser features have been distributed within a very small area of 200 × 200 au2, in spite of a wide velocity range (>100 km s−1). The light curve shows notably intermittent variation and suggests that the H2O masers in G353.273+0.641 are excited by an episodic radio jet. The time-scale of ∼2 yr and characteristic velocity of ∼500 km s−1 also support this interpretation. Two isolated velocity components, C50 (−53 ± 7 km s−1) and C70 (−73 ± 7 km s−1), have shown synchronized linear acceleration of the flux-weighted
values (∼ −5 km s−1 yr−1) during the flare phase. This can be converted to the lower-limit momentum rate of 1.1 × 10−3 M⊙ km s−1 yr−1. The maser properties are quite similar to those of IRAS 20126+4104 especially. This corroborates the previous suggestion that G353.273+0.641 is a candidate high-mass protostellar object. The possible pole-on geometry of the disc-jet system may be suitable for direct imaging of the accretion disc in this case.
We are developing a superconducting camera based on microwave kinetic inductance detectors (MKIDs) to observe 100-GHz continuum with the Nobeyama 45-m telescope. A data acquisition (DAQ) system for ...the camera has been designed to operate the MKIDs with the telescope. This system is required to connect the telescope control system (COSMOS) to the readout system of the MKIDs (MKID DAQ) which employs the frequency-sweeping probe scheme. The DAQ system is also required to record the reference signal of the beam switching for the demodulation by the analysis pipeline in order to suppress the sky fluctuation. The system has to be able to merge and save all data acquired both by the camera and by the telescope, including the cryostat temperature and pressure and the telescope pointing. A collection of software which implements these functions and works as a TCP/IP server on a workstation was developed. The server accepts commands and observation scripts from COSMOS and then issues commands to MKID DAQ to configure and start data acquisition. We made a commissioning of the MKID camera on the Nobeyama 45-m telescope and obtained successful scan signals of the atmosphere and of the Moon.
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