Effective Shielding of 10 GeV Cosmic Rays from Dense Molecular Clumps
arXiv:2301.06716 · doi:10.1038/s41550-022-01868-9
Abstract
The density of cosmic rays inside molecular clouds determines the ionization rate in the dense cores where stars form. It is also one of the drivers of astrochemistry leading to the creation of complex molecules. Through Fermi Large Area Telescope observations of nearby giant molecular clouds, we observed deficits (holes) in the gamma-ray residual map when modelling with the expected gamma-ray diffuse emission from uniform cosmic rays interacting with the molecular content. We propose that the deficit is due to the lack of penetration of the low-energy (sub-GeV to GeV) cosmic rays into denser regions or clumps. This differs from the prevailing view of fast cosmic ray transport in giant molecular clouds where the magnetic turbulence is suppressed by neutral-ion damping, as our results require a slow diffusion inside dense molecular clumps. Through modelling we find that while the shielding is negligible on the cloud scale, it becomes important in the denser, parsec-sized regions where the gravitational collapse is already at play, changing the initial condition of star formation and astrochemistry.
Published in Nature Astronomy
References in corpus (12)
- The Statistics of Supersonic Isothermal Turbulence
- Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
- A Large Catalog of Accurate Distances to Local Molecular Clouds: The Gaia DR2 Edition
- ATLASGAL --- towards a complete sample of massive star forming clumps
- Gamma rays from molecular clouds
- A large catalogue of molecular clouds with accurate distances within 4 kpc of the Galactic disk
- Cosmic ray penetration in diffuse clouds
- The Mass-Size Relation and the Constancy of GMC Surface Densities in the Milky Way
- Criteria for gravitational instability and quasi-isolated gravitational collapse in turbulent medium
- Molecular Outflows in Low- and High-Mass Star Forming Regions
- Density distribution function of a self-gravitating isothermal compressible turbulent fluid in the context of Molecular Clouds ensembles
- Quantifying the interplay between gravity and magnetic field in molecular clouds - a possible multi-scale energy equipartition in NGC6334