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On the relation between magnetic field strength and gas density in the interstellar medium: A multiscale analysis

Lookup NU author(s): Dr Fred Gent

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

© 2025 2025 The Author(s). The relationship between magnetic field strength B and gas density n 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, multiscale broken power-law relation,, with for, and with the field strength at and for For the Zeeman data, we find: for diffuse gas and for dense gas with cm. For the DCF data, we find: And, with cm, where the uncertainties give 68 per cent credible intervals. We perform a similar analysis on nineteen numerical magnetohydrodynamic simulations covering a wide range of physical conditions from protostellar discs to dwarf and Milky Way-like galaxies, computed 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. We find that the dwarf and Milky Way-like galaxy simulations produce results closest to the observations.

Publication metadata

Author(s): Whitworth DJ, Srinivasan S, Pudritz RE, Mac Low M-M, Eadie G, Palau A, Soler JD, Smith RJ, Pattle K, Robinson H, Pillsworth R, Wadsley J, Brucy N, Lebreuilly U, Hennebelle P, Girichidis P, Gent FA, Marin J, Sanchez Valido L, Camacho V, Klessen RS, Vazquez-Semadeni E

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society

Year: 2025

Volume: 540

Issue: 3

Pages: 2762-2786

Print publication date: 01/07/2025

Online publication date: 03/06/2025

Acceptance date: 29/05/2025

Date deposited: 10/07/2025

ISSN (print): 0035-8711

ISSN (electronic): 1365-2966

Publisher: Oxford University Press

URL: https://doi.org/10.1093/mnras/staf901

DOI: 10.1093/mnras/staf901

Data Access Statement: The dwarf galaxy data is available upon request to the first author. For all other data the reader will need to contact the owner of that data as listed in the appropriate reference.

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