The low cosmic-ray density in the Polaris Flare

We reported the γ-ray observation towards the giant molecular cloud Polaris Flare. Together with the dust column density map, we derived the cosmic ray (CR) density and spectrum in this cloud. Compared with the CR measured locally, the CR density in the Polaris Flare is significantly lower and the spectrum is softer. Such a different CR spectrum reveals either a rather large gradient of CR distribution in the direction perpendicular to the Galactic plane or a suppression of CR inside molecular clouds.

Study of the filament WB 673 in ammonia radiolines

We study the molecular filament WB 673 which is located at a distance of 1.8 kpc in the giant molecular cloud G174 + 2.5. Observations of ammonia radiolines NH3 (1,1), (2,2) and (3,3) were carried out in 2019 at the Effelsberg observatory (Germany). The parameters of the lines were determined, maps of the integrated intensities of ammonia in dense clumps WB 668, WB 673, S233-IR and G173.57+2.43 were obtained. The column density of ammonia and the kinetic temperature of the gas were obtained. An analysis of the hyperfine structure anomalies of the NH3 (1,1) lines was carried out.

FOREST unbiased Galactic plane imaging survey with the Nobeyama 45 m telescope (FUGIN). VIII. Possible evidence of cloud–cloud collisions triggering high-mass star formation in the giant molecular cloud M 16 (Eagle Nebula)

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.

ALMA CO observations of a giant molecular cloud in M 33: Evidence for high-mass star formation triggered by cloud–cloud collisions

We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission at a spatial resolution of ∼2 pc. There are two individual molecular clouds with a systematic velocity difference of ∼6 km s−1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V–O7.5V are embedded within the densest parts of molecular clouds bright in the C18O(J = 2–1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼6.2 pc, and show a V-shaped structure in the position–velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud–cloud collisions in the Galactic and Magellanic Cloud H ii regions. Our new finding in M 33 indicates that cloud–cloud collision is a promising process for triggering high-mass star formation in the Local Group.