Molecular cloud formation and magnetic fields in spiral galaxies - AstrophysicsReport as inadecuate

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Abstract: We present ongoing hydrodynamic and MHD simulations of molecular cloudformation in spiral galaxies. The hydrodynamic results show the formation ofmolecular gas clouds where spiral shocks compress atomic gas to high densities.The spiral shocks also produce structure in the spiral arms, provided the gasis cold < 1000 K. When both hot and cold components of the ISM are modeled,this structure is enhanced. Properties such as the clump mass spectra andspatial distribution will be compared from clouds identified in thesesimulations. In particular the multiphase simulations predict the presence ofmuch more interarm molecular gas than when a single phase is assumed. We alsodiscuss very recent results from galactic-scale MHD calculations. Fromobservational comparisons of the magnetic and thermal pressure, magnetic fieldsare expected to be a major factor in explaining the dynamics of the ISM, fromkpc scales to those of star formation. We describe the difference in structureof the spiral arms, and the evolution of the global magnetic field for a rangeof field strengths.

Author: Clare Dobbs, Daniel Price, Ian Bonnell


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