Molecular clouds are complex magnetised structures, with variations over a broad range of length scales. Ionisation in dense, shielded clumps and cores of molecular clouds is thought to be caused by charged cosmic rays (CRs). These CRs can also contribute to heating the gas deep within molecular clouds, and their effect can be substantial when CRs are abundant. CR propagation is predominantly diffusive within disordered magnetised media, and the complex magnetic structures in molecular clouds therefore regulate the spatial propagation and distribution of CRs within them, and hence the local ionisation and heating patterns.
Optical and near-infrared (NIR) polarisation of starlight through molecular clouds can be used to trace magnetic fields. The diffusion coefficients of CRs through magnetised molecular cloud complexes can therefore be inferred from the observed fluctuations in these optical/NIR starlight polarisations. We present our calculations of the expected CR distribution and ionisation/heating patterns in the star-forming filaments of IC 5146, determined from optical/NIR observations. Our calculations show that the local conditions can lead to substantial variations in CR diffusion coefficients. This would affect the local CR heating power and the ionisation rate. These effects are more severe in galaxies that are rich in CRs. The molecular clouds within these galaxies could therefore evolve differently to those in galaxies where CRs are less abundant.
Interstellar clouds, cosmic rays, galactic cosmic rays, interstellar magnetic fields, star formation
|Subcategory||Experimental Methods & Instrumentation|