Topological signatures of interstellar magnetic fields – I. Betti numbers and persistence diagrams. Issue 2 (5th January 2018)

• Record Type: Journal Article
• Authors: Makarenko, Irina; Shukurov, Anvar; Henderson, Robin; Rodrigues, Luiz F S; Bushby, Paul; Fletcher, Andrew
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 475:Issue 2(2018)
• Page Start: 1843
• Page End: 1858
• Publication Date: 2018-01-05
• Subjects: methods: statistical -- ISM: magnetic fields -- ISM: structure; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stx3337
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: The interstellar medium (ISM) is a magnetized system in which transonic or supersonic turbulence is driven by supernova explosions. This leads to the production of intermittent, filamentary structures in the ISM gas density, whilst the associated dynamo action also produces intermittent magnetic fields. The traditional theory of random functions, restricted to second-order statistical moments (or power spectra), does not adequately describe such systems. We apply topological data analysis (TDA), sensitive to all statistical moments and independent of the assumption of Gaussian statistics, to the gas density fluctuations in a magnetohydrodynamic simulation of the multiphase ISM. This simulation admits dynamo action, so produces physically realistic magnetic fields. The topology of the gas distribution, with and without magnetic fields, is quantified in terms of Betti numbers and persistence diagrams. Like the more standard correlation analysis, TDA shows that the ISM gas density is sensitive to the presence of magnetic fields. However, TDA gives us important additional information that cannot be obtained from correlation functions. In particular, the Betti numbers per correlation cell are shown to be physically informative. Magnetic fields make the ISM more homogeneous, reducing the abundance of both isolated gas clouds and cavities, with a stronger effect on the cavities. Remarkably, the modification of the gas distribution by magnetic fields is captured by the Betti numbers even in regions more than 300 pc from the mid-plane, where the magnetic field is weaker and correlation analysis fails to detect any signatures of magnetic effects.