EPoS Contribution
EPoS Contribution
The magnetized interstellar medium: From large galactic to molecular cloud scales

Bastian Koertgen
HS, Hamburg, DE
Magnetic fields are an elemental part of the interstellar medium. However, their impact on gas dynamics and star formation in galaxies remains controversial. We use a suite of global magnetohydrodynamical simulations of isolated disc galaxies to study the influence of magnetic fields on the diffuse and dense gas in the discs. We find that magnetized galaxies undergo a different kind of fragmentation, which is dictated by the Parker instability. Due to the Parker instability, gas can efficiently be transported over kpc distances, while it remains almost unaffected by the magnetic field. Hence, even very strong magnetic fields are seen to not prevent the fragmentation of the galaxies into individual molecular clouds. The different morphology of the fragmentation pattern opens up the route to a varying behavior of star formation in (strongly) magnetized galaxies. However, since no magnetic flux is dragged into the overdense regions formed by the Parker instability, all formed large-scale filaments and dense clouds start out magnetically (super-) critical. We further investigate the morphology of the magnetic field within and around formed molecular clouds and study whether the field orientation in the interstellar medium is preserved in molecular clouds.
Caption: Compendium of column density maps for an example disc galaxy with an initial ratio of thermal to magnetic pressure of 0.25 within the disc. The disc is shown at a time that corresponds to two orbital revolutions at R=8 kpc. The disc has fragmented into individual clouds, which are identified as the yellowish overdense regions (also highlighted in the zoom-in figures). Blue lines denote the orientation of the magnetic field. The latter reveals a rather ordered morphology on large scales in the face-on view. On smaller scales, the distortions depend on position in the galaxy and the local gas/cloud dynamics. A high level of disorder is observed in the edge-on vision.
Collaborators:
R. Banerjee, HS, DE
R. Pudritz, McMa, CA
W. Schmidt, HS, DE
Key publication

Suggested Session: Molecular Clouds