CO, HI, recent Spitzer SAGE results in the Large Magellanic Cloud

Formation of GMCs is one of the most crucial issues in galaxy evolution. I will compare CO and HI in the LMC in 3 dimensional space for the first time aiming at revealing the physical connection between GMCs and associated HI gas at a ~40 pc scale. The present major findings are 1) [total CO intensity] [total HI intensity]0.8 for the 110 GMCs, and 2) the HI intensity tends to increase with the evolution of GMCs. I argue that these findings are consistent with the growth of GMCs via HI accretion over a time scale of a few x 10 Myrs. I will also discuss the role of the background stellar gravity and the dynamical compression by supershells in formation of GMCs

Dust-to-neutral gas ratio of the intermediate velocity HI clouds derived based on the sub-mm dust emission for the whole sky

We derived, as a proxy for the metallicity, the dust-to-HI ratio of the multiple components, the intermediate-velocity clouds (IVCs), the high-velocity clouds (HVCs), and the local HI, by carrying out a multiple-regression analysis of the 21cm HI emission combined with the sub-mm dust optical depth. The method covers over 80 per cent of the sky contiguously at a resolution of 47arcmin and is distinguished from the absorption line measurements toward bright stars covering a tiny fraction of the sky. Major results include that the ratio of the IVCs is in a range of 0.1-1.5 with a mode at 0.6 (relative to the majority of the local ISM, likewise below) and that a significant fraction, ~20 per cent, of the IVCs include dust-poor gas with a ratio of <0.5. It is confirmed that 80 per cent of the HVC Complex C has a ratio of <0.3, and that the Magellanic Stream has a uniform low ratio <0.1. The results prove that some IVCs have low metallicity gas, contrary to the previous absorption line measurements. Considering that the recent works show that the IVCs are interacting and exchanging momentum with the high metallicity Galactic halo gas, we argue that the high metallicity gas contaminates a significant fraction of the IVCs, and the observed fraction of the low metallicity IVCs gives a secure lower limit. Accordingly, we argue the IVCs include a significant fraction of the low metallicity gas supplied from outside the Galaxy as an alternative to the Galactic-fountain model.Comment: 29 pages, 23 figures, submitted to MNRA

Sub-mm/mm studies of the molecular gas in the Galactic disk; the TeV gamma ray SNR RXJ1713.7-3946 and the W28 high mass star forming region

Interstellar molecular clouds are gamma ray sources through the interactions with cosmic ray protons followed by production of neutral pions which decay into gamma rays. We present new NANTEN2 observations of the TeV gamma ray SNR RXJ1713.7-3946 and the W28 region in the 12CO J=2-1, 4-3 and 7-6 emission lines. In RXJ1713.7-3946 we confirm that the local molecular gas having velocities around -10 km/s shows remarkably good spatial correlations with the SNR. We show that the X ray peaks are well correlated with the molecular gas over the whole SNR and suggest that the interactions between the SNR and the molecular gas play an important role in cosmic ray acceleration via several ways including magnetic field compression. The CO J=4-3 distribution towards peak C shows a compact and dense cloud core having a size of about 1 pc as well as a broad wing. The core shows a notable anti-correlation with the Suzaku X ray image and is also associated with hard gamma rays as observed with HESS. Based on these findings, we present a picture that peak C is a molecular clump survived against the impact of the SN blast waves and is surrounded by high energy electrons emitting the X ray. The TeV gamma ray distribution is, on the other hand, more extended into the molecular gas, supporting the hadronic origin of gamma ray production. W28 is one of the most outstanding star forming regions exhibiting TeV gamma rays as identified through a comparison between the NANTEN CO dataset and HESS gamma ray sources. In the W28 region, we show the CO J=2-1 distribution over the whole region as well as the detailed image of the two TeV gamma ray peaks. One of them show strong CO J=7-6 emission, suggesting high excitation conditions in this high mass star forming core. A pursuit for the detailed mechanism to produce gamma rays is in progress.Comment: 9 pages, 8 Encapsulated Postscript figures, uses aipxfm.sty aipproc.cls aip-6s.clo aip-8d.clo aip-8s.cl