Kimihiro Kimura

High-mass cloud cores in the η carinae giant molecular cloud

We carried out an unbiased survey for massive dense cores in the giant molecular cloud associated with η Carinae with the NANTEN telescope in the 12CO, 13CO, and C18O J = 1-0 emission lines. We identified 15 C18O cores, whose typical line width ΔVcomp, radius r, mass M, column density N(H2), and average number density n(H2) were 3.3 km s-1, 2.2 pc, 2.6 × 103 M☉, 1.3 × 1022 cm-2, and 1.2 × 103 cm-3, respectively. Two of the 15 cores are associated with IRAS point sources whose luminosities are larger than 104 L☉, which indicates that massive star formation is occurring within these cores. Five cores, including the two with IRAS sources, are associated with MSX point sources. We detected H13CO+ (J = 1-0) emission toward four C18O cores, two of which are associated with IRAS and MSX point sources; another one is associated only with an MSX point source, and the other is associated with neither IRAS nor MSX point sources. The core with neither IRAS nor MSX point sources shows the presence of a bipolar molecular outflow in 12CO (J = 2-1), which indicates that star formation is also occurring in the core, and the other three of the four H13CO+ detections show winglike emission. In total, 6 C18O cores out of 15 (=40%) have experienced star formation, and at least 2 of 15 (=13%) are massive star-forming cores in the η Car GMC. We found that massive star formation occurs preferentially in cores with larger N(H2), M, and n(H2) and a smaller ratio of Mvir/M. We also found that the cores in the η Car GMC are characterized by large ΔV and Mvir/M on average compared to the cores in other GMCs observed with the same telescope. These properties of the cores may account for the fact that as much as 60%-87% of the cores do not show any signs of massive star formation. We investigated the origin of a large amount of turbulence in the η Car GMC. We found that turbulence injection from stellar winds, molecular outflows, and supernova remnants that originated from stars formed within the GMC are not enough to explain the existing turbulence. We propose the possibility that the large turbulence was preexisting when the GMC was formed and is now dissipating. Mechanisms such as multiple supernova explosions in the Carina flare supershell may have contributed to form a GMC with a large amount of turbulence.

A New 100-GHz Band Front-End System with a Waveguide-Type Dual-Polarization Sideband-Separating SIS Receiver for the NRO 45-m Radio Telescope

We developed a waveguide-type dual-polarization sideband-separating SIS receiver system of the 100GHz band for the 45-m radio telescope at the Nobeyama Radio Observatory, Japan. This receiver is composed of an ortho-mode transducer and two sideband-separating SIS mixers, which are both based on the waveguide technique. The receiver has four intermediate frequency bands of 4.0–8.0 GHz. Over the radio frequency range of 80–120 GHz, the single-sideband receiver noise temperatures are 50–100 K and the image rejection ratios are greater than 10 dB. We developed new matching optics for the telescope beam as well as new IF chains for the four IF signals. The new receiver system was installed in the telescope, and we successfully observed the 12 CO, 13 CO and C 18 O emission lines simultaneously toward the Sagittarius B2 region to confirm the performance of the receiver system. The SSB noise temperature of the system, including the atmosphere, became approximately half of that of the previous receiver system. The Image Rejection Ratios (IRRs) of the two 2SB mixers were calculated from the 12 CO and HCO + spectra from the W51 giant molecular cloud, resulting in > 20 dB for one polarization and > 12 dB for the other polarization.

Molecular Clumps and Infrared Clusters in the S247, S252, and BFS52 Regions

We present results of the observations carried out toward the S247, S252, and BFS52 H II regions with various molecular lines using the 1.85?m radio telescope and the 45?m telescope at Nobeyama Radio Observatory. There are at least 11 young infrared clusters (IR clusters) within the observed region. We found that there are two velocity components in 12CO?(J = 2-1), and also that their spatial distributions show an anti-correlation. The IR clusters are located at their interfaces, suggesting that two distinct clouds with different velocities are colliding with each other, which may have induced the cluster formation. Based on 13CO?(J = 1-0) and C18O (J = 1-0) observations, we identified 16 clumps in and around the three H II regions. Eleven of the clumps are associated with the IR clusters and the other five clumps are not associated with any known young stellar objects. We investigated variations in the velocity dispersions of the 16 clumps as a function of the distance from the center of the clusters or the clumps. Clumps with clusters tend to have velocity dispersions that increase with distance from the cluster center, while clumps without clusters show a flat velocity dispersion over the clump extents. A 12CO?outflow has been found in some of the clumps with IR clusters but not in the other clumps, supporting a strong relation of these clumps to the broader velocity dispersion region. We also estimated a mean star formation efficiency of ~30% for the clumps with IR clusters in the three H II regions.

A New 60-cm Radio Survey Telescope with the Sideband-Separating SIS Receiver for the 200 GHz Band

We have upgraded the 60-cm radio survey telescope located in Nobeyama, Japan. We developed a new waveguide-type sideband-separating SIS mixer for the telescope, which enables the simultaneous detection of distinct molecular emission lines both in the upper and lower sidebands. Over the RF frequency range of 205-240 GHz, the single-sideband receiver noise temperatures of the new mixer are 40-100 K for the 4.0-8.0 GHz IF frequency band. The image rejection ratios are greater than 10 dB over the same range. For the dual IF signals obtained by the receiver, we have developed two sets of acousto-optical spectrometers and a telescope control system. Using the new telescope system, we successfully detected the 12CO (J=2-1) and 13CO (J=2-1) emission lines simultaneously toward Orion KL in 2005 March. Using the waveguide-type sideband-separating SIS mixer for the 200 GHz band, we have initiated the first simultaneous 12CO (J=2-1) and 13CO (J=2-1) survey of the galactic plane as well as large-scale mapping observations of nearby molecular clouds.

Observations of 6.7 GHz methanol masers with East-Asian VLBI Network. I. VLBI images of the first epoch of observations

Very-long-baseline interferometry (VLBI) monitoring of the 6.7 GHz methanol maser allows us to measure the internal proper motion of maser spots and therefore study the gas motion around high-mass young stellar objects. To this end, we have begun monitoring observations with the East-Asian VLBI Network. In this paper we present the results of the first epoch observation for 36 sources, including 35 VLBI images of the methanol maser. Since two independent sources were found in three images, images of 38 sources were obtained. In 34 sources, 10 or more spots were detected. The observed spatial scale of the maser distribution was from 9 to 4900 astronomical units, and the following morphological categories were observed: elliptical, arched, linear, paired, and complex. The position of the maser spot was determined with an accuracy of approximately 0.1 mas, which is sufficiently high to measure the internal proper motion from two years of monitoring observations. The VLBI observation, however, detected only approximately 20% of all maser emissions, suggesting that the remaining 80% of the total flux was spread into an undetectable extended distribution. Therefore, in addition to high-resolution observations, it is important to observe the whole structure of the maser emission including extended low-brightness structures, in order to reveal the associated site of the maser and gas motion.

Initial Results from Nobeyama Molecular Gas Observations of Distant Bright Galaxies

We present initial results from the CO survey toward high redshift galaxies using the Nobeyama 45m telescope. Using the new wide bandwidth spectrometer equipped with a two-beam SIS receiver, we have robust new detections of three high redshift (z=1.6-3.4) submillimeter galaxies (SXDF 1100.001, SDP9, and SDP17), one tentative detection (SDSS J160705+533558), and one non-detection (COSMOS-AzTEC1). The galaxies observed during the commissioning phase are sources with known spectroscopic redshifts from previous optical or from wide-band submm spectroscopy. The derived molecular gas mass and line widths from Gaussian fits are ~10^11 Msun and 430-530 km/s, which are consistent with previous CO observations of distant submm galaxies and quasars. The spectrometer that allows a maximum of 32 GHz instantaneous bandwidth will provide new science capabilities at the Nobeyama 45m telescope, allowing us to determine redshifts of bright submm selected galaxies without any prior redshift information.

High-mass star formation possibly triggered by cloud–cloud collision in the H ii region RCW 34

We report a possibility that the high-mass star located in the HII region RCW 34 was formed by a triggering induced by a collision of molecular clouds. Molecular gas distributions of the

LiteBIRD: mission overview and design tradeoffs

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Exploration of Southern Sky with Atacama Submillimeter Telescope Experiment (ASTE)

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RCW 36 in the Vela Molecular Ridge: Evidence for high-mass star-cluster formation triggered by cloud–cloud collision

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