COLD MILKY WAY H i GAS IN FILAMENTS

Kalberla, P. M. W.; Kerp, J.; Haud, U.; Winkel, B.; Bekhti, N. Ben; Flöer, L.; Lenz, Daniel

doi:10.3847/0004-637x/821/2/117

Cited by 79 publications

(107 citation statements)

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“…1 with isophotes. These structures are typical for the filamentary CNM described by Kalberla et al (2016).…”

Section: Source Selectionmentioning

confidence: 73%

“…For the northern sky there is the Galactic Effelsberg-Bonn Hi Survey (EBHIS, , in the south the Parkes Galactic All Sky Survey (GASS, McClure-Griffiths et al 2009;Kalberla et al 2010). Kalberla et al (2016), merging EBHIS with the 3rd release of the GASS (GASS III, Kalberla & Haud 2015), have shown that the cold neutral medium (CNM) in the local vicinity is mostly organized in filaments. A comparison with structures measured by Planck at 353 GHz (Planck Collaboration et al 2016) disclosed that the CNM filaments are well aligned with the thermal dust emission.…”

Section: Introductionmentioning

confidence: 99%

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Anisotropies in the HI gas distribution toward 3C 196

Kalberla

Kerp

2016

A&A

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Context. The local Galactic Hi gas was found to contain cold neutral medium (CNM) filaments that are aligned with polarized dust emission. These filaments appear to be dominated by the magnetic field and in this case turbulence is expected to show distinct anisotropies. Aims. We use the Galactic Effelsberg-Bonn Hi Survey (EBHIS) to derive 2D turbulence spectra for the Hi distribution in direction to 3C 196 and two more comparison fields. Methods. Prior to Fourier transform we apply a rotational symmetric 50% Tukey window to apodize the data. We derive average as well as position angle dependent power spectra. Anisotropies in the power distribution are defined as the ratio of the spectral power in orthogonal directions. Results. We find strong anisotropies. For a narrow range in position angle, in direction perpendicular to the filaments and the magnetic field, the spectral power is on average more than an order of magnitude larger than parallel. In the most extreme case the anisotropy reaches locally a factor of 130. Anisotropies increase on average with spatial frequency as predicted by Goldreich and Sridhar, at the same time the Kolmogorov spectral index remains almost unchanged. The strongest anisotropies are observable for a narrow range in velocity and decay with a power law index close to -8/3, almost identical to the average isotropic spectral index of −2.9 < γ < −2.6. Conclusions. Hi filaments, associated with linear polarization structures in LOFAR observations in direction to 3C 196, show turbulence spectra with marked anisotropies. Decaying anisotropies appear to indicate that we witness an ongoing shock passing the Hi and affecting the observed Faraday depth.

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“…1 with isophotes. These structures are typical for the filamentary CNM described by Kalberla et al (2016).…”

Section: Source Selectionmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Anisotropies in the HI gas distribution toward 3C 196

Kalberla

Kerp

2016

A&A

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“…New methods of analysis are required that do not rely on the assumption of Gaussian statistics or weak deviations from it and are sensitive to morphological and topological properties of the random fields. For example, the nature of filamentary structures (Kalberla et al 2016) prominent in both observations and many numerical simulations of interstellar gas requires reliable determination of their dimensions (see Makarenko et al 2015;Kalberla et al 2016, for examples of such analysis). The need for new methods of statistical comparison between theory and observations is discussed in an insightful review of Goodman (2011) and by Koch et al (2017) who employ genus statistics, a topological measure earlier applied to the matter distribution in the cosmic web (Gott et al 1987, and many later papers).…”

Section: Discussionmentioning

confidence: 99%

Topological signatures of interstellar magnetic fields – I. Betti numbers and persistence diagrams

Makarenko

Shukurov

Henderson

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The interstellar medium (ISM) is a magnetised 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 (MHD) simulation of the multi-phase 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 midplane, where the magnetic field is weaker and correlation analysis fails to detect any signatures of magnetic effects.

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“…XXXII 2016;Planck Collaboration Int. XXXVIII 2016;Kalberla et al 2016), the GMF orientation is correlated with the structure of matter as traced by H i or dust emission. Our modelling does not include the density structure of the ISM, nor does it include the correlation between matter and the magnetic field orientation; however, the polarization layers could phenomenologically represent distinct matter structures along the LOS.…”

Section: Density Structure Of the Ismmentioning

confidence: 99%

“…An important result is that in the diffuse ISM, the filamentary structure of matter is observed to be statistically aligned with the GMF (McClure-Griffiths et al 2006;Clark et al 2014;Planck Collaboration Int. XXXII 2016;Kalberla et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Planckintermediate results

Aghanim

Alves

Arzoumanian

et al. 2016

A&A

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Using data from the Planck satellite, we study the statistical properties of interstellar dust polarization at high Galactic latitudes around the south pole (b < −60• ). Our aim is to advance the understanding of the magnetized interstellar medium (ISM), and to provide a modelling framework of the polarized dust foreground for use in cosmic microwave background (CMB) component-separation procedures. We examine the Stokes I, Q, and U maps at 353 GHz, and particularly the statistical distribution of the polarization fraction (p) and angle (ψ), in order to characterize the ordered and turbulent components of the Galactic magnetic field (GMF) in the solar neighbourhood. The Q and U maps show patterns at large angular scales, which we relate to the mean orientation of the GMF towards Galactic coordinates (l 0 , b 0 ) = (70The histogram of the observed p values shows a wide dispersion up to 25%. The histogram of ψ has a standard deviation of 12• about the regular pattern expected from the ordered GMF. We build a phenomenological model that connects the distributions of p and ψ to a statistical description of the turbulent component of the GMF, assuming a uniform effective polarization fraction (p 0 ) of dust emission. To compute the Stokes parameters, we approximate the integration along the line of sight (LOS) as a sum over a set of N independent polarization layers, in each of which the turbulent component of the GMF is obtained from Gaussian realizations of a power-law power spectrum. We are able to reproduce the observed p and ψ distributions using a p 0 value of 26%, a ratio of 0.9 between the strengths of the turbulent and mean components of the GMF, and a small value of N. The mean value of p (inferred from the fit of the large-scale patterns in the Stokes maps) is 12 ± 1%. We relate the polarization layers to the density structure and to the correlation length of the GMF along the LOS. We emphasize the simplicity of our model (involving only a few parameters), which can be easily computed on the celestial sphere to produce simulated maps of dust polarization. Our work is an important step towards a model that can be used to assess the accuracy of component-separation methods in present and future CMB experiments designed to search the B mode CMB polarization from primordial gravity waves.Key words. magnetohydrodynamics (MHD) -polarization -methods: data analysis -dust, extinction -cosmic background radiation -ISM: magnetic fields IntroductionInterstellar magnetic fields are tied to the interstellar gas. Together with cosmic rays they form a dynamical system that Corresponding author: A. Bracco, e-mail: andrea.bracco@cea.fr is an important (but debated) facet of the physics of galaxies. Magnetic fields play a pivotal role because they control the density and distribution of cosmic rays, and they act on the dynamics if the gas. Much of the physics involved in this interplay is encoded in the structure of interstellar magnetic fields. Observations of synchrotron emission and its polarization, asArticle pu...

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COLD MILKY WAY H i GAS IN FILAMENTS

Cited by 79 publications

References 50 publications

Anisotropies in the HI gas distribution toward 3C 196

Anisotropies in the HI gas distribution toward 3C 196

Topological signatures of interstellar magnetic fields – I. Betti numbers and persistence diagrams

Planckintermediate results

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