2024/07/25 by David J Whitworth, Whitworth, D. J., S. Srinivasan +24 · 3 citations
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Magnetic and Electromagnetic Effects
paper · pdf · doi:10.48550/arxiv.2407.18293
openalex publication_date 2024/07/25 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The magnetic field strength to gas density relation in the interstellar medium is of fundamental importance. We present and compare Bayesian analyses of the B-n relation for two comprehensive observational data sets: a Zeeman data set and 700 observations using the Davis-Chandrasekhar-Fermi (DCF) method. Using a hierarchical Bayesian analysis we present a general, multi-scale broken power-law relation, B=B0(n/n0)α , with α=α1 for nn0, and with B0 the field strength at n0. For the Zeeman data we find: α1=0.15+0.06-0.09 for diffuse gas and α2 = 0.53+0.09-0.07 for dense gas with n0 = 4.00+12.7-2.90 × 103 cm-3. For the DCF data we find: α1=0.26+0.15-0.15 and α2=0.77-0.15+0.14, with n0=13.9+10.1-7.30 × 104 cm-3, where the uncertainties give 68% credible intervals. We perform a similar analysis on nineteen numerical magnetohydrodynamic simulations covering a wide range of physical conditions from protostellar disks to dwarf and Milky Way-like galaxies, completed with the AREPO, Flash, Pencil, and Ramses codes. The resulting exponents depend on several physical factors such as dynamo effects and their time scales, turbulence, and initial seed field strength. \textcolorredWe find that the dwarf and Milky Way-like galaxy simulations produce results closest to the observations.