2018/07/31 by Shigeki Inoue, Naoki Yoshida · 17 citations
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Geomagnetism and Paleomagnetism Studies #Instability #Mechanics #Physics #Solar and Space Plasma Dynamics #Spiral (railway) #Spiral galaxy #Stars #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.1093/mnras/stz584
published in Monthly Notices of the Royal Astronomical Society 485(3), 3024-3041 (Oxford University Press) · 17 pages, 13 figures,submitted to MNRAS, analysis part (Section2) was significantly revised reflecting reviewer's comments
openalex created_date 2018/07/19 · arxiv created 2018/12/11 · openalex publication_date 2019/02/26 · arxiv updated 2019/03/06 · openalex updated_date 2026/08/05
ABSTRACT Fragmentation of spiral arms can drive the formation of giant clumps and induce intense star formation in disc galaxies. Based on the spiral-arm instability analysis of our Paper I, we present linear perturbation theory of dynamical instability of self-gravitating spiral arms of magnetized gas, focusing on the effect of toroidal magnetic fields. Spiral arms can be destabilized by the toroidal fields that reduce Coriolis force, i.e. magneto-Jeans instability. Our analysis can be applied to multicomponent systems that consist of gas and stars. To test our analysis, we perform ideal magneto-hydrodynamics simulations of isolated disc galaxies and examine the simulation results. We find that our analysis can characterize dynamical instability leading arms to fragment and form clumps if magnetic fields are nearly toroidal. We propose that dimensionless growth rate of the most unstable perturbation, which is computed from our analysis, can be used to predict fragmentation of spiral arms within an orbital time-scale. Our analysis is applicable as long as magnetic fields are nearly toroidal. Using our analytic model, we estimate a typical mass of clumps forming from spiral-arm fragmentation to be consistent with observed giant clumps ∼107–8 M⊙. Furthermore, we find that, although the magnetic destabilization can cause low-density spiral arms to fragment, the estimated mass of resultant clumps is almost independent from strength of magnetic fields since marginal instability occurs at long wavelengths that compensate the low densities of magnetically destabilized arms.