We study Gamma-ray supernova remnant W49B and its environment using recent radio and infrared data. Spitzer IRS low resolution data of W49B shows shocked excitation lines of H 2 (0,0) S(0)-S(7) from the SNR-molecular cloud interaction. The H 2 gas is composed of two components with temperature of ∼260 K and ∼1060 K respectively. Various spectral lines from atomic and ionic particles are detected towards W49B. We suggest the ionic phase has an electron density of ∼500 cm −3 and a temperature of ∼10 4 K by the spectral line diagnoses. The mid-and farinfrared data from MSX, Spitzer and Herschel reveals a 151 ± 20 K hot dust component with a mass of 7.5 ± 6.6 × 10 −4 M ⊙ and a 45 ± 4 K warm dust component with a mass of 6.4 ± 3.2 M ⊙ . The hot dust is likely from materials swept up by the shock of W49B. The warm dust may possibly originate from the evaporation of clouds interacting with W49B. We build the HI absorption spectra of W49B and nearby four Hii regions (W49A, G42.90+0.58, G42.43-0.26 and G43.19-0.53), and study the relation between W49B and the surrounding molecular clouds by employing the 2.12 µm infrared and CO data. We therefore obtain a kinematic distance of ∼10 kpc for W49B and suggest that the remnant is likely associated with the CO cloud at about 40 km s −1 .

We present CO observations of 78 spiral galaxies in local merger pairs. These galaxies represent a subsample of a K s -band selected sample consisting of 88 close major-merger pairs (HKPAIRs), 44 spiral-spiral (S+S) pairs and 44 spiral-elliptical (S+E) pairs, with separation < 20 h −1 kpc and mass ratio < 2.5. For all objects, the star formation rate (SFR) and dust mass were derived from Herschel PACS and SPIRE data, and the atomic gas mass, M HI , from the Green Bank Telescope HI observations. The complete data set allows us to study the relation between the gas (atomic and molecular) mass, dust mass and SFR in merger galaxies. We derive the molecular gas fraction (M H 2 /M * ), molecular-to-atomic gas mass ratio (M H 2 /M HI ), gas-to-dust mass ratio and SFE (=SFR/M H 2 ) and study their dependences on pair type (S+S compared to S+E), stellar mass and the presence of morphological interaction signs. We find an overall moderate enhancements (∼ 2×) in both molecular gas fraction (M H 2 /M * ), and molecular-to-atomic gas ratio (M H 2 /M HI ) for star-forming galaxies in major-merger pairs compared to non-interacting comparison samples, whereas no enhancement was found for the SFE nor for the total gas mass fraction ((M HI +M H 2 )/M * ). When divided into S+S and S+E, low mass and high mass, and with and without interaction signs, there is a small difference in SFE, moderate difference in M H 2 /M * , and strong differences in M H 2 /M HI between subsamples. For the molecular-to-atomic gas ratio M H 2 /M HI , the difference between S+S and S+E subsamples is 0.69± 0.16 dex and between pairs with and without interaction signs is 0.53± 0.18 dex. Together, our results suggest (1) star formation enhancement in close major-merger pairs occurs mainly in S+S pairs after the first close encounter (indicated by interaction signs) because the HI gas is compressed into star-forming molecular gas by the tidal torque; (2) this effect is much weakened in the S+E pairs.

We present a study of the Hi gas content of a large K-band selected sample of 88 close major-merger pairs of galaxies (H-KPAIR) which were observed by Herschel . We obtained the 21 cm Hi finestructure emission line data for a total of 70 pairs from this sample, by observing 58 pairs using the Green Bank Telescope (GBT) and retrieving the Hi data for an addition 12 pairs from the literature. In this Hi sample, 34 pairs are spiral-spiral (S+S) pairs, and 36 are spiral-elliptical (S+E). Based on these data, we studied the Hi-to-stellar mass ratio, the Hi gas fraction and the Hi star formation efficiency (SFE Hi = star formation rate/M Hi ) and searched for differences between S+S and S+E pairs, as well as between pairs with and without signs for merger/interaction. Our results showed that the mean Hi-to-stellar mass ratio of spirals in these pairs is = 7.6 ± 1.0%, consistent with the average Hi gas fraction of spiral galaxies in general. The differences in the Hi gas fraction between spirals in S+S and in S+E pairs, and between spirals in pairs with and without signs of merger/interaction are insignificant (< 1σ). On the other hand, the mean SFE Hi of S+S pairs is ∼ 4.6× higher than that of S+E pairs. This difference is very significant (∼ 4σ) and is the main result of our study. There is no significant difference in the mean SFE Hi between galaxies with and without signs of merger/interaction. The mean SFE Hi of the whole pair sample is 10 −9.55±0.09 yr −1 , corresponding to a Hi consumption time of 3.5 ± 0.7 Gyrs.

The low dust temperatures (<14 K) of Planck Galactic cold clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. "TOP-SCOPE" is a joint survey program targeting ∼2000 PGCCs in J=1-0 transitions of CO isotopologues and ∼1000 PGCCs in 850 μm continuum emission. The objective of the "TOP-SCOPE" survey and the joint surveys (SMT 10 m, KVN 21 m, and NRO 45 m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis, and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, length, and mean line mass (M/L) of the G26 filament are ∼6200 M ☉ , ∼12 pc, and ∼500 M ☉ pc −1 , respectively. Ten massive clumps, including eight starless ones, are found along the filament. The most massive clump as a whole may still be in global collapse, while its denser part seems to be undergoing expansion owing to outflow feedback. The fragmentation in the G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, nonmagnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index (β) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed owing to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.