Cold neutral medium (CNM) is an intermediate stage between the diffuse warm neutral hydrogen (HI) and the dense molecular hydrogen (H2) in interstellar media (ISM) and is a current frontier in galaxy evolution and cosmology research due to its prevalence, favorable physical properties, and important role in determining the polarized galactic foreground.
Observations suggest that CNM is typically cold, turbulent, highly filamentary and preferentially oriented parallel to the magnetic field. However, theory suggests that CNM may not exhibit the same degree of filamentation and may be oriented perpendicular to the magnetic field.
To resolve this discrepancy, the project proposes high-resolution simulations with realistic chemistry and magnetohydrodynamics (MHD). Our simulations will investigate the physical and chemical evolutions of the CNM, and its interaction with the magnetic field, and its formation from the surrounding contracting unstable neutral medium (UNM).
The study of CNM via high-resolution numerical simulations is a crucial step in understanding the eventual star formation, as CNM is a precursor to the molecular clouds within which stars form. The results of the simulations will help reconcile observations and theory and provide insight into the formation and evolution of CNM filaments.
The Max Planck Institute for Extraterrestrial Physics, Germany;
University of Wisconsin–Madison, Germany.