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

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-Chandrasekh...

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Main Authors: Whitworth, David J. (Author) , Srinivasan, S (Author) , Pudritz, R E (Author) , Mac Low, M -M (Author) , Eadie, G (Author) , Palau, A (Author) , Soler, J D (Author) , Smith, R J (Author) , Pattle, K (Author) , Robinson, H (Author) , Pillsworth, R (Author) , Wadsley, J (Author) , Brucy, N (Author) , Lebreuilly, U (Author) , Hennebelle, P (Author) , Girichidis, Philipp (Author) , Gent, F A (Author) , Marin, J (Author) , Sánchez Valido, L (Author) , Camacho, V (Author) , Klessen, Ralf S. (Author) , Vázquez-Semadeni, E (Author)
Format: Article (Journal)
Language:English
Published: July 2025
In: Monthly notices of the Royal Astronomical Society
Year: 2025, Volume: 540, Issue: 3, Pages: 2762-2786
ISSN:1365-2966
DOI:10.1093/mnras/staf901
Online Access:Verlag, kostenfrei, Volltext: https://doi.org/10.1093/mnras/staf901
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Author Notes:D.J. Whitworth, S. Srinivasan, R.E. Pudritz, M.-M. Mac Low, G. Eadie, A. Palau, J.D. Soler, R.J. Smith, K. Pattle, H. Robinson, R. Pillsworth, J. Wadsley, N. Brucy, U. Lebreuilly, P. Hennebelle, P. Girichidis, F.A. Gent, J. Marin, L. Sánchez Valido, V. Camacho, R.S. Klessen and E. Vázquez-Semadeni
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Summary: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, $B=B_0(n/n_0)^{\alpha }$, with $\alpha =\alpha _1$ for $n< n_0$ and $\alpha _2$ for $n>n_0$, and with $B_0$ the field strength at $n_0$. For the Zeeman data, we find: $\alpha _1={0.15^{+0.06}_{-0.09}}$ for diffuse gas and $\alpha _2 = {0.53^{+0.09}_{-0.07}}$ for dense gas with $n_0 = 0.40^{+1.30}_{-0.30}\times 10^4$ cm$^{-3}$. For the DCF data, we find: $\alpha _1={0.26^{+0.01}_{-0.01}}$ and $\alpha _2={0.77_{-0.15}^{+0.14}}$, with $n_0=14.00^{+10.00}_{-7.00}\times 10^4$ cm$^{-3}$, 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.
Item Description:Veröffentlicht: 03. Juni 2025
Gesehen am 29.10.2025
Physical Description:Online Resource
ISSN:1365-2966
DOI:10.1093/mnras/staf901

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