In the past twenty years, the reconnaissance of 12 CO and 13 CO emission in the Milky Way by single-dish millimeter-wave telescopes has expanded our view and understanding of interstellar molecular gas. We enumerate the major surveys of CO emission along the Galactic plane and summarize the various approaches that leverage these data to determine the large-scale distribution of molecular gas: its radial and vertical distributions, its concentration into clouds, and its relationship to spiral structure. The integrated properties of molecular clouds are compiled from catalogs derived from the CO surveys using uniform assumptions regarding the Galactic rotation curve, solar radius, and the CO-to-H2 conversion factor. We discuss the radial variations of cloud surface brightness, the distributions of cloud mass and size, and scaling relations between velocity dispersion, cloud size, and surface density that affirm that the larger clouds are gravitationally bound. Measures of density structure and gas kinematics within nearby, well-resolved clouds are examined and attributed to the effects of magnetohydrodynamic turbulence. We review the arguments for short, intermediate, and long molecular lifetimes based on the observational record. The review concludes with questions that shall require further observational attention.

Molecular Clouds in the Milky Way

The data from a CO(1 - 0) mapping survey of 40 nearby spiral galaxies performed with the Nobeyama 45-m telescope are presented. The criteria of the sample selection were (1) RC3 morphological type in the range Sa to Scd, (2) distance less than 25 Mpc, (3) inclination angle less than 79deg (RC3), (4) flux at 100 um higher than ~ 10 Jy, (5) spiral structure is not destroyed by interaction. The maps of CO cover most of the optical disk of the galaxies. We investigated the influence of bar on the distribution of molecular gas in spiral galaxies using these data. We confirmed that the degree of central concentration is higher in barred spirals than in non-barred spirals as shown by the previous works. Furthermore, we present an observational evidence that bars are efficient in driving molecular gas that lies within the bar length toward the center, while the role in bringing gas in from the outer parts of the disks is small. The transported gas accounts for about half of molecular gas within the central region in barred spiral galaxies. We found a correlation between the degree of central concentration and bar strength. Galaxies with stronger bars tend to have higher central concentration. The correlation implies that stronger bars accumulate molecular gas toward the center more efficiently. These results are consistent with long-lived bars.

/pdf/nobeyama-co-atlas-of-nearby-spiral-galaxies-distribution-of-12ut84ez69.pdf

Nobeyama CO Atlas of Nearby Spiral Galaxies: Distribution of Molecular Gas in Barred and Nonbarred Spiral Galaxies

We have developed a spectral line On-The-Fly (OTF) observing mode for the Nobeyama Radio Observatory 45-m and the Atacama Submillimeter Telescope Experiment 10-m telescopes. Sets of digital autocorrelation spectrometers are available for OTF with heterodyne receivers mounted on the telescopes, including the focal-plane 5
 $\times$ 
5 array receiver, BEARS, on the 45-m. During OTF observations, the antenna is continuously driven to cover the mapped region rapidly, resulting in a high observing efficiency and accuracy. Pointing of the antenna and readouts from the spectrometer are recorded as fast as 0.1s. In this paper we report on improvements made to the software and instruments, requirements and optimization of observing parameters, the data-reduction process, and verification of the system. It is confirmed that, using optimal parameters, the OTF is about twice as efficient as the conventional position-switch observing method.

/pdf/on-the-fly-observing-system-of-the-nobeyama-45-m-and-aste-10-al517hzdae.pdf

On-The-Fly Observing System of the Nobeyama 45-m and ASTE 10-m Telescopes

We have mapped the northern area (30' ? 20') of a Local Group spiral galaxy M33 in 12CO(J = 1-0) line with the 45 m telescope at the Nobeyama Radio Observatory. Along with H? and Spitzer 24 ?m data, we have investigated the relationship between the surface density of molecular gas mass and that of star formation rate (SFR) in an external galaxy (Kennicutt-Schmidt law) with the highest spatial resolution (~80 pc) to date, which is comparable to scales of giant molecular clouds (GMCs). At positions where CO is significantly detected, the SFR surface density exhibits a wide range of over four orders of magnitude, from ?SFR 10?10 to ~10?6 M ? yr?1 pc?2, whereas the values are mostly within 10-40 M ? pc?2. The surface density of gas and that of SFR correlate well at an ~1 kpc resolution, but the correlation becomes looser with higher resolution and breaks down at GMC scales. The scatter of the ?SFR- relationship in the ~80?pc resolution results from the variety of star-forming activity among GMCs, which is attributed to the various evolutionary stages of GMCs and to the drift of young clusters from their parent GMCs. This result shows that the Kennicutt-Schmidt law is valid only in scales larger than that of GMCs, when we average the spatial offset between GMCs and star-forming regions, and their various evolutionary stages.

https://iopscience.iop.org/article/10.1088/2041-8205/722/2/L127/pdf

Breakdown of kennicutt–schmidt law at giant molecular cloud scales in m33

On the basis of near-infrared imaging observations, we derived the visual extinction (AV) distribution toward 10 Bok globules through measurements of both the color excess (EH-K) and the stellar density at J, H, and Ks (star count). Radial column density profiles for each globule were analyzed with the Bonnor-Ebert sphere model. Using the data of our 10 globules and four globules in the literature, we investigated the stability of globules on the basis of ξmax, which characterizes the Bonnor-Ebert sphere, as well as the stability of the equilibrium state against gravitational collapse. We found that more than half the starless globules are located near the critical state (ξmax = 6.5 ± 2). Thus, we suggest that a nearly critical Bonnor-Ebert sphere characterizes the typical density structure of starless globules. The remaining starless globules show clearly unstable states (ξmax > 10). Since unstable equilibrium states are not long maintained, we expect that these globules are on the way to gravitational collapse or that they are stabilized by nonthermal support. It was also found that all the star-forming globules show unstable solutions of ξmax > 10, which is consistent with the fact that they have started gravitational collapse. We investigated the evolution of a collapsing gas sphere whose initial condition is a nearly critical Bonnor-Ebert sphere. We found that the column density profiles of the collapsing sphere mimic those of the static Bonnor-Ebert spheres in unstable equilibrium. The collapsing gas sphere resembles marginally unstable Bonnor-Ebert spheres for a long time. We found that the frequency distribution of ξmax for the observed starless globules is consistent with that from model calculations of the collapsing sphere. In addition to the near-infrared observations, we carried out radio molecular line observations (C18O and N2H + ) toward the same 10 globules. We confirmed that most of the globules are dominated by thermal support. The line width of each globule was used to estimate the cloud temperature including the contribution from turbulence, with which we estimated the distance to the globules from the Bonnor-Ebert model fitting.

/pdf/near-infrared-imaging-survey-of-bok-globules-density-o4xybraz2q.pdf

Near-Infrared Imaging Survey of Bok Globules: Density Structure

A large focal plane array receiver system for the NRO 45 m telescope (SIS 25-BEam Array Receiver System, or BEARS) is described. This new array receiver uses SIS junctions and has 25 elements. It can operate at the frequency range of 82 - 116 GHz. The development of this new system is almost complete. We describe about the whole system in detail, which includes the receiver, the IF systems, the new spectrometers and the remote control systems. We also describe about the performances and the uniformity of the system and show the astronomical result.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

BEARS. SIS 25-BEam Array Receiver System for the NRO 45-m Telescope.

The design of the new 5x5 SIS focal plane array receiver for the 45-rn telescope at the Nobeyama Radio Observatory (NRO) is described. It is called BEARS (SIS 25-BEam rray eceiver system). This receiver has 25 elements. It covers thefrequency range from 82 to 1 16GHz. The array uses SIS junctions mounted in fixed tuned mixer blocks. The meanDSB receiver noise temperature is about 75 K at all the LO frequencies. The standard deviation of the receiver noise temperature is about 20K. The receiver was installed on the telescope and has been used for observations and measurements since April 1998. The design of the receiver system, the optics and the heat model will be presented in thispaper.Keywords: SIS receiver, Focal plane array receiver, Radio Astronomy, Millimeter wave 1. INTRODUCTION In order to observe astronomical objects like galaxies and molecular clouds in our Galaxy, the standard method to get a mapis that an object is observed by scanning one point after another in sequence. However, the demands to observe a wide areawith high resolution and high sensitivity become greater recently. The 45 m telescope is playing an important role in theobservation because it can realize observations with high resolution and high sensitivity. These capabilities give rise to ademerit. It is difficult to observe a wide area. Because the number of observation points becomes great and it takes a longtime to survey a wide area. One of the ways to resolve this demerit is to reduce the noise of the receiver, which dominatesthe majority of the system noise. SIS receivers have very low noise characteristics and can be expected to have quantum-

Chieko Yamaguchi

Papers

BEARS. SIS 25-BEam Array Receiver System for the NRO 45-m Telescope.

Design of the focal plane array receiver for the NRO 45-m telescope