Yoshinori Yonekura

The Second Survey of the Molecular Clouds in the Large Magellanic Cloud by NANTEN. I. Catalog of Molecular Clouds

The second survey of the molecular clouds in the Large Magellanic Cloud in 12CO ( -->J = 1?0) 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 -->MCO 2 ? 104 M?. 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 -->Mvir LCO1.1 ? 0.1, 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 XCO-factor of ~ -->7 ? 1020 cm?2 (K km s?1)?1. The mass spectrum of the clouds is fitted well by a power law of -->Ncloud(> MCO) MCO?0.75 ? 0.06 above the completeness limit of -->5 ? 104 M?. The slope of the mass spectrum becomes steeper if we fit only the massive clouds, e.g., -->Ncloud(> MCO) MCO?1.2 ? 0.2 for -->MCO ? 3 ? 105 M?.

A PAN-CARINA YOUNG STELLAR OBJECT CATALOG: INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE CARINA NEBULA IDENTIFIED VIA MID-INFRARED EXCESS EMISSION

We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42 deg2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumstellar disks and envelopes, using data from the Spitzer Space Telescope (the Vela-Carina survey) and the Two-Micron All Sky Survey. We model the 1-24 μm IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 M ☉ 2 × 104 YSOs and a present-day star formation rate (SFR) of >0.008 M ☉ yr–1. The global SFR in the Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.

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.

Clumpy photon-dominated regions in Carina - I. [C I] and mid-J CO lines in two 4'

Context. The Carina region is an excellent astrophysical laboratory for studying the feedback mechanisms of newly born, very massive stars within their natal giant molecular clouds (GMCs) at only 2.35 kpc distance. Aims. We use a clumpy PDR model to analyse the observed intensities of atomic carbon and CO and to derive the excitation conditions of the gas. Methods. The NANTEN2-4 m submillimeter telescope was used to map the [C i] 3 P1− 3 P0, 3 P2− 3 P1 and CO 4–3, 7–6 lines in two 4 � × 4 � regions of Carina where molecular material interfaces with radiation from the massive star clusters. One region is the northern molecular cloud near the compact OB cluster Tr 14, and the second region is in the molecular cloud south of η Car and Tr 16. These data were combined with 13 CO SEST spectra, HIRES/IRAS 60 µm and 100 µm maps of the FIR continuum, and maps of 8 µm IRAC/Spitzer and MSX emission. Results. We used the HIRES far-infrared dust data to create a map of the FUV field heating the gas. The northern region shows an FUV fi eld of af ew 10 3 in Draine units while the field of the southern region is about a factor 10 weaker. While the IRAC 8 µm emission lights up at the edges of the molecular clouds, CO and also [C i] appear to trace the H2 gas column density. The northern region shows a complex velocity and spatial structure, while the southern region shows an edge-on PDR with a single Gaussian velocity component. We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the 38 �� beam (0.43 pc), which follow canonical power-law mass and mass-size distributions. We find that an average local clump density of 2 × 10 5 cm −3 is needed to reproduce the observed line emission at two selected interface positions. Conclusions. Stationary, clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.

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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.

4' fields

We present the results of C18O observations by the 45 m Nobeyama radio telescope toward dense clumps with young clusters in nine massive star-forming regions. We identified 39 clumps whose mass, radius, and line width range from 15 to 1500 M?, from 0.14 to 0.76 pc, and from 0.6 to 3.2 km s-1, respectively. The clumps associated with massive (proto)stars have a large line width (~2.5 km s-1) and a large mass (~500 M?). Most of the clumps are sufficiently gravitationally bound because they have a virial mass similar to the gas mass, and the average H2 density of the clumps increases with increasing internal kinetic motion. Next, we found two relations, one between the number density of associated 2MASS sources and the average H2 density of the clump and the other between the number density of sources and the star formation efficiency of the clump. From these results, we suggest that a structure, whose size scale is ~0.3 pc, with a high average H2 density is required in order for cluster formation to occur. In addition, we found that the internal kinetic motion of a clump has to be large in order to form massive stars, because there is a good correlation between the maximum mass of associated stars and the line width of the clump. Such clumps with large internal motion must generally have a high average H2 density in order to be gravitationally bound. Thus, massive stars are formed in a dense cluster.

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 describe detailed simulations of X-ray-emitting populations to evaluate the levels of contamination by both Galactic and extragalactic X-ray sources unrelated to a star-forming region under study. For Galactic contaminations, we consider contribution from main-sequence stars and giants (not including cataclysmic variables and other classes of accretion-driven X-ray binary systems), as they make the dominant contribution at the position of the Carina Nebula. The simulations take into consideration a variety of technical factors involving a Galactic population synthesis model, stellar X-ray luminosity functions, Chandra telescope response, source detection methodology, and possible spatial variations in the X-ray background and absorption through molecular clouds. When applied to the 1.42 deg2 field of the Chandra Carina Complex Project (CCCP), the simulations predict ~5000 contaminating sources (1 source arcmin–2 of the survey), evenly distributed across the field. The results of the simulations are further employed in a companion CCCP study to assign membership probabilities to individual sources.

Dense Molecular Clumps Associated with Young Clusters in Massive Star-forming Regions

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.

SOURCE CONTAMINATION IN X-RAY STUDIES OF STAR-FORMING REGIONS: APPLICATION TO THE CHANDRA CARINA COMPLEX PROJECT

We report Mopra Australia Telescope National Facility (ATNF), Anglo-Australian Telescope and Atacama Submillimeter Telescope Experiment observations of a molecular clump in Carina, BYF73 = G286.21+0.17, which give evidence of large-scale gravitational infall in the dense gas. From the millimetre and far-infrared data, the clump has a mass of ~2 x 10 4 M ⊙ , luminosity of ~2-3 x 10 4 L ⊙ and diameter of ~0.9 pc. From radiative transfer modelling, we derive a mass infall rate of ~3.4 x 10 -2 M ⊙ yr -1 . If confirmed, this rate for gravitational infall in a molecular core or clump may be the highest yet seen. The near-infrared K-band imaging shows an adjacent compact H II region and IR cluster surrounded by a shell-like photodissociation region showing H 2 emission. At the molecular infall peak, the K imaging also reveals a deeply embedded group of stars with associated H 2 emission. The combination of these features is very unusual, and we suggest that they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation.

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

Studying molecular gas in the central regions of the star burst galaxies NGC4945 and Circinus enables us to characterize the physical conditions and compare them to previous local and high-z studies. We estimate temperature, molecular density and column densities of CO and atomic carbon. Using model predictions we give a range of estimated CO/C abundance ratios. Using the new NANTEN2 4m sub-millimeter telescope in Pampa La Bola, Chile, we observed for the first time CO 4-3 and [CI] 3P1-3 P0 at the centers of both galaxies at linear scale of 682 pc and 732 pc respectively. We compute the cooling curves of 12CO and 13CO using radiative transfer models and estimate the physical conditions of CO and [CI]. The centers of NGC4945 and Circinus are very [CI] bright objects, exhibiting [CI] 3P1 - 3 P0 luminosities of 91 and 67Kkms-1kpc2, respectively. The [CI] 3P1-3 P0/CO 4-3 ratio of integrated intensities are large at 1.2 in NGC4945 and 2.8 in Circinus. Combining previous CO J= 1-0, 2-1 and 3-2 and 13CO J= 1-0, 2-1 studies with our new observations, the radiative transfer calculations give a range of densities, n(H2) = 10^3-3*104^cm-3, and a wide range of kinetic temperatures, Tkin = 20 - 100K, depending on the density. Future CO J= 7-6 and [CI] 2-1 observations will be important to resolve the ambiguity in the physical conditions and confirm the model predictions.