The physical and the geometrical properties of simulated cold H <scp>i</scp> structures

Gazol, Adriana; Villagran, Marco A.

doi:10.1093/mnras/staa3852

Cited by 8 publications

(6 citation statements)

References 63 publications

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“…The density at which this correlation becomes significant (n H < ∼ 30 cm −3 ) depends on the initial conditions but is not sensitive to the presence of self-gravity. Figure 2 of Gazol & Villagran (2021) shows that the resulting clumps have a wide range of magnetic field intensities, which is similar to the large scatter that we observe here. The magnetic field in the simulations, albeit weak, qualitatively affects the morphology by producing filamentary structures.…”

Section: Filaments At the Rim Of The The Local Bubblesupporting

confidence: 84%

“…Studying the nature and the properties of the cold structures formed via thermal instability in the magnetized atomic ISM, Gazol & Villagran (2018) and Gazol & Villagran (2021) searched for clumps formed in forced MHD simulations with an initial magnetic field ranging from 0 to 8.3 µG. These authors find that a positive correlation between B and n H develops for all initial magnetic field intensities.…”

Section: Filaments At the Rim Of The The Local Bubblementioning

confidence: 99%

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Aspect ratios of far-infrared and H i filaments in the diffuse interstellar medium at high Galactic latitudes

Kalberla¹,

Haud²

2023

Preprint

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Context. Dusty magnetized structures observable in the far-infrared (FIR) at high Galactic latitudes are ubiquitous and found to be closely related to H i filaments with coherent velocity structures. Aims. Considering dimensionless morphological characteristics based on Minkowski functionals, we determine the distribution of filamentarities F and aspect ratios A for these structures. Methods. Our data are based on Planck FIR and HI4PI H i observations. Filaments have previously been extracted by applying the Hessian operator. We trace individual filamentary structures along the plane of the sky and determine A and F . Results. Filaments in the diffuse interstellar medium (ISM) are seldom isolated structures, but are rather part of a network of filaments with a well-defined, continuous distribution in A and F . This distribution is self-replicating, and the merger or disruption of individual filamentary structures leads only to a repositioning of the filament in A and F without changing the course of the distribution. Conclusions. FIR and H i filaments identified at high Galactic latitudes are a close match to model expectations for narrow filaments with approximately constant widths. This distribution is continuous without clear upper limits on the observed aspect ratios. Filaments are associated with enhanced column densities of CO-dark H 2 . Radial velocities along the filaments are coherent and mostly linear with typical dispersions of ∆v LSR = 5.24 km s −1 . The magnetic field strength in the diffuse turbulent ISM scales with hydrogen volume density as B ∝ n 0.58 H . At high Galactic latitudes, we determine an average turbulent magnetic field strength of δB = 5.3 µG and an average mean strength of the magnetic field in the plane of the sky of B POS = 4.4 µG.

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Section: Filaments At the Rim Of The The Local Bubblesupporting

confidence: 84%

Section: Filaments At the Rim Of The The Local Bubblementioning

confidence: 99%

Aspect ratios of far-infrared and H i filaments in the diffuse interstellar medium at high Galactic latitudes

Kalberla¹,

Haud²

2023

Preprint

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“…The morphologies of CNM structures contain imprints of a complex interplay between thermal instability, shock compression, turbulence, and magnetic fields at different scales. The connections between CNM morphology and the conditions of its multiscale turbulent ISM environment have been studied with numerical simulations (Hennebelle et al 2007;Saury et al 2014;Inoue & Inutsuka 2016;Gazol & Villagran 2021;Fielding et al 2022). The ST, with its set of interpretable coefficients at different scales and orientations, can enable convenient quantitative comparisons between observations and simulations.…”

Section: Discussionmentioning

confidence: 99%

Probing the Cold Neutral Medium through H I Emission Morphology with the Scattering Transform

Lei

Clark

2023

ApJ

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Neutral hydrogen (H I) emission exhibits complex morphology that encodes rich information about the physics of the interstellar medium. We apply the scattering transform (ST) to characterize the H I emission structure via a set of compact and interpretable coefficients, and find a connection between the H I emission morphology and H I cold neutral medium (CNM) phase content. Where H I absorption measurements are unavailable, the H I phase structure is typically estimated from the emission via spectral line decomposition. Here, we present a new probe of the CNM content using measures that are solely derived from H I emission spatial information. We apply the ST to GALFA-H I data at high Galactic latitudes ( b > 30 ° ), and compare the resulting coefficients to CNM fraction measurements derived from archival H I emission and absorption spectra. We quantify the correlation between the ST coefficients and the measured CNM fraction (f CNM), finding that the H I emission morphology encodes substantial f CNM-correlating information and that ST-based metrics for small-scale linearity are particularly predictive of f CNM. This is further corroborated by the enhancement of the I 857/N HI ratio with larger ST measures of small-scale linearity. These results are consistent with the picture of regions with higher CNM content being more populated by small-scale filamentary H I structures. Our work illustrates a physical connection between the H I morphology and phase content, and suggests that future phase decomposition methods can be improved by making use of both H I spectral and spatial information.

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Section: Introductionmentioning

confidence: 99%

“…From simulations, it has been suggested that filamentary H structures can be formed by turbulence, shocks, or thermal instabilities, with the role of the magnetic field still under debate (e.g., Hennebelle 2013;Federrath 2016b;Inoue & Inutsuka 2016;Villagran & Gazol 2018;Gazol & Villagran 2021). In fact, various numerical studies have led to results ranging from no preferred orientation of the H filaments with respect to the magnetic field (Federrath 2016b), to the filaments preferentially oriented parallel (Inoue & Inutsuka 2016;Villagran & Gazol 2018) or perpendicular (Gazol & Villagran 2021) to the magnetic field. Extending the observational study of the relative orientation between magnetic fields and H filamentary structures to nearby galaxies is therefore crucial, as the simpler external perspective will allow us to verify, despite the very different spatial scales probed, if the magnetically aligned H filaments are a general trend across a vast galactic volume.…”

Section: Introductionmentioning

confidence: 99%

HI filaments as potential compass needles? Comparing the magnetic field structure of the Small Magellanic Cloud to the orientation of GASKAP-HI filaments

Ma¹,

McClure‐Griffiths²,

Clark³

et al. 2023

Preprint

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High-spatial-resolution H observations have led to the realisation that the nearby (within few hundreds of parsecs) Galactic atomic filamentary structures are aligned with the ambient magnetic field. Enabled by the high quality data from the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope for the Galactic ASKAP H (GASKAP-H ) survey, we investigate the potential magnetic alignment of the 10 pc-scale H filaments in the Small Magellanic Cloud (SMC). Using the Rolling Hough Transform (RHT) technique that automatically identifies filamentary structures, combined with our newly devised raytracing algorithm that compares the H and starlight polarisation data, we find that the H filaments in the northeastern end of the SMC main body ("Bar" region) and the transition area between the main body and the tidal feature ("Wing" region) appear preferentially aligned with the magnetic field traced by starlight polarisation. Meanwhile, the remaining SMC volume lacks starlight polarisation data of sufficient quality to draw any conclusions. This suggests for the first time that filamentary H structures can be magnetically aligned across a large spatial volume ( kpc) outside of the Milky Way. In addition, we generate maps of the preferred orientation of H filaments throughout the entire SMC, revealing the highly complex gaseous structures of the galaxy likely shaped by a combination of the intrinsic internal gas dynamics, tidal interactions, and star formation feedback processes. These maps can further be compared with future measurements of the magnetic structures in other regions of the SMC.

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The physical and the geometrical properties of simulated cold H i structures

Cited by 8 publications

References 63 publications

Aspect ratios of far-infrared and H i filaments in the diffuse interstellar medium at high Galactic latitudes

Aspect ratios of far-infrared and H i filaments in the diffuse interstellar medium at high Galactic latitudes

Probing the Cold Neutral Medium through H I Emission Morphology with the Scattering Transform

HI filaments as potential compass needles? Comparing the magnetic field structure of the Small Magellanic Cloud to the orientation of GASKAP-HI filaments

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