2004/07/19 by Gilberto C. Gómez, Gilberto C. Gomez, Donald P. Cox +1 · 5 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Solar and Space Plasma Dynamics #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/424499
published as Astrophys.J. 615 (2004) 744-757 · Accepted for publication in ApJ. Better quality figures in http://www.astro.umd.edu/~gomez/publica/3d_galaxy-2.pdf
arxiv created 2004/07/19 · openalex publication_date 2004/11/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
As we have discussed previously, the extra stiffness that a magnetic field adds to the interstellar medium (ISM) changes the way the ISM reacts to the presence of a spiral perturbation. At intermediate to high z , the gas shoots up before the arm, then flows over and falls behind the arm as it approaches the next arm. This generates a multicell circulation pattern, within each of which the net radial mass flux is positive near the midplane and negative at higher z . The flow distorts the magnetic field lines. In the arm region, the gas flows nearly parallel to the arm, and therefore the magnetic field adopts a similar pitch angle. Between the arms, the gas flows out in radius, generating a negative pitch angle in the magnetic field. The intensity and direction of the field yield synthetic synchrotron maps that reproduce some features of the synchrotron maps of external galaxies, such as the islands of emission and the displacement between the gaseous and synchrotron arms. When comparing the magnitude of the field with the local gas density, two distinctive relations appear, depending on whether the magnetic pressure is dominant. Above the plane, the density structure develops a shape resembling a breaking wave. This structure collapses and rises again with a period of about 60 Myr, similar to that of a vertical oscillation mode. The falling gas plays an important part in the overall hydrostatics, since its deceleration compresses the low- z gas, raising the average midplane pressure in the interarm region above that provided by the weight of the material above.