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.

We performed new large-scale 12CO, 13CO, and C18O J = 1–0 observations of the W 43 giant molecular cloud complex in the tangential direction of the Scutum arm (l ∼30°) as a part of the FUGIN project. The low-density gas traced by 12CO is distributed over 150 pc × 100 pc (l × b), and has a large velocity dispersion (20–30 km s−1). However, the dense gas traced by C18O is localized in the W 43 Main, G30.5, and W 43 South (G29.96−0.02) high-mass star-forming regions in the W 43 giant molecular cloud (GMC) complex, which have clumpy structures. We found at least two clouds with a velocity difference of ∼10–20 km s−1, both of which are likely to be physically associated with these high-mass star-forming regions based on the results of high 13CO J = 3–2 to J = 1–0 intensity ratio and morphological correspondence with the infrared dust emission. The velocity separation of these clouds in W 43 Main, G30.5, and W 43 South is too large for each cloud to be gravitationally bound. We also revealed that the dense gas in the W 43 GMC has a high local column density, while “the current SFE” (star formation efficiency) of the entire GMC is low ($\sim\!\! 4\%$) compared with the W 51 and M 17 GMC. We argue that the supersonic cloud–cloud collision hypothesis can explain the origin of the local mini-starbursts and dense gas formation in the W 43 GMC complex.

We carried out 12 CO(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 × 10 48 erg.

Recent observations of the nearby Galactic molecular clouds indicate that the dense gas in molecular clouds have quasi-universal properties on star formation, and observational studies of extra-galaxies have shown a galactic-scale correlation between the star formation rate (SFR) and surface density of molecular gas. To reach a comprehensive understanding of both properties, it is important to quantify the fractional mass of the dense gas in molecular clouds f DG . In particular, for the Milky Way (MW), there are no previous studies resolving the f DG disk over a scale of several kpc. In this study, the f DG was measured over 5 kpc in the first quadrant of the MW, based on the CO J=1-0 data in l = 10 • -50 • obtained as part of the FOREST Unbiased Galactic Plane Imaging Survey with the Nobeyama 45-m Telescope (FUGIN) project. The total molecular mass was measured using 12 CO, and the dense gas mass was estimated using C 18 O. The fractional masses including f DG in the region within ±30% of the distances to the tangential points of the Galactic rotation (e.g., the Galactic Bar, Far-3kpc Arm, Norma Arm, Scutum Arm, Sagittarius Arm, and inter-arm regions) were measured. As a result, an averaged f DG of 2.9 +2.6 −2.6 % was obtained for the entirety of the target region. This low value suggests that dense gas formation is the primary factor of inefficient star formation in galaxies. It was also found that the f DG shows large variations depending on the structures in the MW disk. The f DG in the Galactic arms were estimated to be ∼ 4-5%, while those in the bar and inter-arm regions were as small as ∼ 0.1-0.4%. These results indicate that the formation/destruction processes of the dense gas and their timescales are different for different regions in the MW, leading to the differences in SFRs.

We observed molecular clouds in the W33 high-mass star-forming region associated with compact and extended H II regions using the NANTEN2 telescope as well as the Nobeyama 45-m telescope in the J =1-0 transitions of 12 CO, 13 CO, and C 18 O as a part of the FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) legacy survey. We detected three velocity components at 35 km s −1 , 45 km s −1 , and 58 km s −1 . The 35 km s −1 and 58 km s −1 clouds are likely to be physically associated with W33 because of the enhanced 12 CO J = 3-2 to J =1-0 intensity ratio as R 3−2/1−0 > 1.0 due to the ultraviolet irradiation by OB stars, and morphological correspondence between the distributions of molecular gas and the infrared and radio continuum emissions excited by high-mass stars. The two clouds show complementary distributions around W33. The velocity separation is too large to be gravitationally bound, and yet not explained by expanding motion by stellar feedback. c 2014. Astronomical Society of Japan. 2Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 Therefore, we discuss that a cloud-cloud collision scenario likely explains the high-mass star formation in W33.

Sh2-48 is a Galactic HII region located at 3.8 kpc with an O9.5-type star identified at its center.As a part of the FOREST Unbiased Galactic plane Imaging survey using the Nobeyama 45m telescope (FUGIN) project, we obtained the CO J=1-0 dataset for a large area of Sh2-48 at a spatial resolution of 21 ′′ (∼0.4 pc), which we used to find a molecular cloud with a total molecular mass of ∼ 3.8 × 10 4 M ⊙ associated with Sh2-48. The molecular cloud has a systematic velocity shift within a velocity range ∼42-47 km s −1 . On the lower velocity side the CO emission spatially corresponds with the bright 8 µm filament at the western rim of Sh2-48, while the CO emission at higher velocities is separated at the eastern and western sides of the 8 µm filament. This velocity change forms V-shaped, east-west-oriented feature on the position-velocity diagram. We found that these lower and higher-velocity components are, unlike the infrared and radio continuum data, physically associated with Sh2-48. To interpret the observed V-shaped velocity distribution, we assessed a cloud-cloud collision scenario and found from a comparison between the observations and simulations that the velocity distribution is an expected outcome of a collision between a cylindrical cloud and a spherical cloud, with the cylindrical cloud corresponding to the lower-velocity component, and the two separated components in the higher-velocity part interpretable as the collision-broken remnants of the spherical cloud. Based on the consistency of the ∼1.3 Myr estimated formation timescale of the HII region with that of the collision, we concluded that the high-mass star formation in Sh2-48 was triggered by the collision.

We present 12 CO (J=1-0), 13 CO (J=1-0) and C 18 O (J=1-0) images of the M17 giant molecular clouds obtained as part of FUGIN (FOREST Ultra-wide Galactic Plane Survey InNobeyama) project. The observations cover the entire area of M17 SW and M17 N clouds at the highest angular resolution (∼19 ′′ ) to date which corresponds to ∼ 0.15 pc at the distance of 2.0 kpc. We find that the region consists of four different velocity components: very low velocity (VLV) clump, low velocity component (LVC), main velocity component (MVC), and high velocity component (HVC). The LVC and the HVC have cavities. UV photons radiated from NGC 6618 cluster penetrate into the N cloud up to ∼ 5 pc through the cavities and interact with molecular gas. This interaction is correlated with the distribution of YSOs in the N cloud.The LVC and the HVC are distributed complementary after that the HVC is displaced by 0.8 pc toward the east-southeast direction, suggesting that collision of the LVC and the HVC create the cavities in both clouds. The collision velocity and timescale are estimated to be 9.9 km s −1 and 1.1×10 5 yr, respectively. The high collision velocity can provide the mass accretion rate up to 10 −3 M ⊙ yr −1 , and the high column density (4 × 10 23 cm −2 ) might result in massive cluster formation. The scenario of cloud-cloud collision likely well explains the stellar population and its formation history of NGC 6618 cluster proposed by Hoffmeister et al. (2008).

M 16, the Eagle Nebula, is an outstanding H ii region which exhibits extensive high-mass star formation and hosts remarkable “pillars.” We herein obtained new 12COJ = 1–0 data for the region observed with NANTEN2, which were combined with the 12COJ = 1–0 data obtained using the FOREST unbiased galactic plane imaging with Nobeyama 45 m telescope (FUGIN) survey. These observations revealed that a giant molecular cloud (GMC) of ∼1.3 × 105 M⊙ is associated with M 16, which extends for 30 pc perpendicularly to the galactic plane, at a distance of 1.8 kpc. This GMC can be divided into the northern (N) cloud, the eastern (E) filament, the southeastern (SE) cloud, the southeastern (SE) filament, and the southern (S) cloud. We also found two velocity components (blueshifted and redshifted components) in the N cloud. The blueshifted component shows a ring-like structure, and the redshifted one coincides with the intensity depression of the ring-like structure. The position–velocity diagram of the components showed a V-shaped velocity feature. The spatial and velocity structures of the cloud indicated that two different velocity components collided with each other at a relative velocity of 11.6 km s−1. The timescale of the collision was estimated to be ∼4 × 105 yr. The collision event reasonably explains the formation of the O9V star ALS 15348, as well as the shape of the Spitzer bubble N19. A similar velocity structure was found in the SE cloud, which is associated with the O7.5V star HD 168504. In addition, the complementary distributions of the two velocity components found in the entire GMC suggested that the collision event occurred globally. On the basis of the above results, we herein propose a hypothesis that the collision between the two components occurred sequentially over the last several 106 yr and triggered the formation of O-type stars in the NGC 6611 cluster in M 16.