We present a quantitative atlas and catalog of dark clouds derived by using the optical database “Digitized Sky Survey I”. Applying a traditional star-count technique to 1043 plates contained in the database, we produced an $A_V$ map covering the entire region in the galactic latitude range $\vert b\vert \le 40^\circ$. The map was drawn at two different angular resolutions of $6'$ and $18'$, and is shown in detail in a series of figures in this paper. Based on the $A_V$ map, we identified 2448 dark clouds and 2841 clumps located inside them. Some physical parameters, such as the position, extent, and optical extinction, were measured for each of the clouds and clumps. We also searched for counterparts among already known dark clouds in the literature. The catalog of dark clouds presented in this paper lists the cloud parameters as well as the counterparts.

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The “$\int$-shaped filament” of the Orion A giant molecular cloud was mapped in N$_2$H$^+$, and its northern end, the OMC-2/3 region, was also observed in HC$_3$N and CCS. The results were compared with maps of other molecular lines and the dust continuum emission. The N$_2$H$^+$ distribution is similar to the dust continuum distribution, except for the central part of the Orion Nebula. The distribution of H$^{13}$CO$^+$ holds a resemblance to that of the dust continuum, but the N$_2$H$^+$ distribution looks more similar to the dust continuum distribution. The N-bearing molecules, N$_2$H$^+$ and NH$_3$, seem to be more intense in OMC-2, compared with the H$^{13}$CO$^+$ and CS distribution. This suggests that OMC-2 has a higher abundance of N-bearing molecules, or a higher filling factor of the quiescent gas. We identified 34 cloud cores from N$_2$H$^+$ data. Over the Orion Nebula region, the N$_2$H$^+$ linewidth is large (1.1-2.1kms$^{-1}$). In the OMC-2/3 region, it becomes moderate (0.5-1.3kms$^{-1}$), and it is smaller (0.3-1.1kms$^{-1}$) in the south of the Orion Nebula. On the other hand, the gas kinetic temperature of the quiescent cores observed in N$_2$H$^+$ is rather constant ($\sim$20K) over the $\int$-shaped filament. We detected no CCS emission in the OMC-2/3 region. In general, the N$_2$H$^+$ and HC$_3$N distribution is quite similar in the OMC-2/3 region, but we observed a displacement between N$_2$H$^+$ and HC$_3$N over a 2$\prime$ scale in OMC-3, which has a chain of Class 0-I protostars (candidates).

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We have measured the ortho-to-para ratio of ammonia in the blueshifted gas of the L1157 outflow by observing the six metastable inversion lines from &parl0;J,K&parr0;=&parl0;1,1&parr0; to (6, 6). The highly excited (5, 5) and (6, 6) lines were first detected in the low-mass star-forming regions. The rotational temperature derived from the ratio of four transition lines from (3, 3) to (6, 6) is 130-140 K, suggesting that the blueshifted gas is heated by a factor of approximately 10 as compared to the quiescent gas. The ortho-to-para ratio of the NH3 molecules in the blueshifted gas is estimated to be 1.3-1.7, which is higher than the statistical equilibrium value. This ratio provides us with evidence that the NH3 molecules have been evaporated from dust grains with the formation temperature between 18 and 25 K. It is most likely that the NH3 molecules on dust grains have been released into the gas phase through the passage of strong shock waves produced by the outflow. Such a scenario is supported by the fact that the ammonia abundance in the blueshifted gas is enhanced by a factor of approximately 5 with respect to the dense quiescent gas.

We have analyzed the angular momentum of the molecular cloud cores in the Orion A giant molecular cloud observed in the N 2 H + J = 1 → 0 line with the Nobeyama 45 m radio telescope. We have measured the velocity gradient using position velocity diagrams passing through core centers, and made sinusoidal fitting against the position angle. 27 out of 34 N 2 H + cores allowed us to measure the velocity gradient without serious confusion. The derived velocity gradient ranges from 0.5 to 7.8 km s −1 pc −1 . We marginally found that the specific angular momentum J/M (against the core radius R) of the Orion N 2 H + cores tends to be systematically larger than that of molecular cloud cores in cold dark clouds obtained by Goodman et al., in the J/M − R relation. The ratio β of rotational to gravitational energy is derived to be β = 10 −2.3±0.7 , and is similar to that obtained for cold dark cloud cores in a consistent definition. The large-scale rotation of the -shaped filament of the Orion A giant molecular cloud does not likely govern the core rotation at smaller scales.

The FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) project is one of the legacy projects using the new multi-beam FOREST receiver installed on the Nobeyama 45-m telescope. This project aims to investigate the distribution, kinematics, and physical properties of both diffuse and dense molecular gas in the Galaxy at once by observing 12 CO, 13 CO, and C 18 O J = 1 − 0 lines simultaneously. The mapping regions are a part of the 1st quadrant (10• ) of the Galaxy, where spiral arms, bar structure, and the molecular gas ring are included. This survey achieves the highest angular resolution to date (∼20 ′′ ) for the Galactic plane survey in the CO J = 1 − 0 lines, which makes it possible to find dense clumps located farther away than the previous surveys. FUGIN will provide us with an invaluable dataset for investigating the physics of the galactic interstellar medium (ISM), particularly the evolution of interstellar gas covering galactic scale structures to the internal structures of giant molecular clouds, such as small filament/clump/core. We present an overview of the FUGIN project, observation plan, and initial results, which reveal wide-field and detailed structures of molecular clouds, such as entangled filaments that have not been obvious in previous surveys, and large-scale kinematics of molecular gas such as spiral arms.