Gaussian decomposition of H I surveys

Haud, U.

doi:10.1051/0004-6361:20078922

Cited by 14 publications

(15 citation statements)

References 32 publications

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“…Neutral clouds within the disk-halo interface (z ∼ 1-2 kpc) show up with cold cores and warm enveloping gas. This two-phase structure is observed toward all IVCs and the bulk of the HVCs , Haud 2008. Cores have on average larger infall velocities than envelopes.…”

Section: Column Density Structure Of High Galactic Altitude Cloudsmentioning

confidence: 76%

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The Hi Distribution of the Milky Way

Kalberla

2009

Annu. Rev. Astron. Astrophys.

427

383

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Neutral atomic hydrogen (Hi) traces the interstellar medium (ISM) over a broad range of physical conditions. Its 21-cm emission line is a key probe of the structure and dynamics of the Milky Way Galaxy. About 50 years after the first detection of the 21-cm line the exploration of the Hi distribution of the Milky Way has undergone a true renaissance. This was triggered by several large-scale 21-cm surveys that became available within the past decade. New all-sky surveys unravel the shape and volume density distribution of the gaseous disk up to its borders. High-resolution Galactic plane surveys disclose a wealth of shells, filaments, and spurs that bear witness to the recycling of matter between stars and the ISM. All these observational results indicate that the Hi gas traces a dynamical Galactic ISM with structures on all scales, from tens of astronomical units to kiloparsecs. The Galaxy can be considered to be a violent, breathing disk surrounded by highly turbulent extra-planar gas.

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Section: Column Density Structure Of High Galactic Altitude Cloudsmentioning

confidence: 76%

“…HVCs, in comparison to IVCs, not only have higher velocities but are also smaller and have fainter cores. Their envelopes show also a larger velocity dispersion (Haud 2008).…”

Section: Column Density Structure Of High Galactic Altitude Cloudsmentioning

confidence: 97%

The Hi Distribution of the Milky Way

Kalberla

2009

Annu. Rev. Astron. Astrophys.

427

383

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“…These features are thought to be located in the Galactic halo, IVCs at kpc distances and probably originating from a Galactic fountain and HVCs at larger distances with an external origin (Wakker & van Woerden (1997) and van Woerden et al (2004)). Both cloud types have a two-phase structure, but are distinct from Galactic H i because of their morphology and their distribution in center velocities and velocity widths (Haud, 2008). We consider the question of how much the IVC and HVC power spectra differ from the local distribution.…”

Section: Introductionmentioning

confidence: 99%

Turbulent power distribution in the local interstellar medium

Kalberla¹,

Haud

2019

A&A

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Context. The interstellar medium (ISM) on all scales is full of structures that can be used as tracers of processes that feed turbulence. Aims. We used H i survey data to derive global properties of the angular power distribution of the local ISM. Methods. HI4PI observations on an nside = 1024 HEALPix grid and Gaussian components representing three phases, the cold, warm, and unstable lukewarm neutral medium (CNM, WNM, and LNM), were used for velocities |v LSR | ≤ 25 km s −1 . For high latitudes |b| > 20 • we generated apodized maps. After beam deconvolution we fitted angular power spectra. Results. Power spectra for observed column densities are exceptionally well defined and straight in log-log presentation with 3D power law indices γ ≥ −3 for the local gas. For intermediate velocity clouds (IVCs) we derive γ = −2.6 and for high velocity clouds (HVCs) γ = −2.0. Single-phase power distributions for the CNM, LNM, and WNM are highly correlated and shallow with γ ∼ −2.5 for multipoles l ≤ 100. Excess power from cold filamentary structures is observed at larger multipoles. The steepest single-channel power spectra for the CNM are found at velocities with large CNM and low WNM phase fractions. Conclusions. The phase space distribution in the local ISM is configured by phase transitions and needs to be described with three distinct different phases, being highly correlated but having distributions with different properties. Phase transitions cause locally hierarchical structures in phase space. The CNM is structured on small scales and is restricted in position-velocity space. The LNM as an interface to the WNM envelops the CNM. It extends to larger scales than the CNM and covers a wider range of velocities. Correlations between the phases are self-similar in velocity.

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“…Proceeding from these considerations, in the first paper of this series (Haud 2000, hereafter Paper I) we described a new fully automated computer programme for the decomposition of large 21-cm H  line surveys into Gaussian components. We used the Leiden/Dwingeloo Survey (LDS) of galactic neutral hydrogen (Hartmann 1994) as test data for decomposition.…”

Section: Introductionmentioning

confidence: 99%

Gaussian decomposition of $\ion{H}{i}$ surveys

Haud

Kalberla²

2007

A&A

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Aims. We investigate the properties of the 21-cm radio-lines of galactic neutral hydrogen by decomposing, the profiles of "The Leiden/Argentine/Bonn (LAB) Survey of Galactic H " into Gaussian components. The width distribution of the obtained components is analysed and compared with similar studies by other authors.Methods. The study is based on an automatic profile decomposition algorithm. As the Gaussians obtained for the complex H  profiles near the galactic plane cannot be directly interpreted in terms of the properties of gas clouds, we mainly study the selected simplest profiles in a limited velocity range. The selection criteria are described and their influence on the results is discussed.Results. Considering only the simplest H  profiles, we demonstrate that for Gaussians with relatively small LSR velocities (−9 ≤ V C ≤ 4 km s −1 ) it is possible to distinguish three or four groups of preferred line-widths. The mean widths of these groups are FWHM = 3.9 ± 0.6, 11.8 ± 0.5, 24.1 ± 0.6, and 42 ± 5 km s −1 . Verschuur previously proposed similar line-width regimes, but with somewhat larger widths. He used a human-assisted decomposition for a nearly 50 times smaller database and we discuss systematic differences in analysis and results. Conclusions. The line-widths of about 3.9 and 24.1 km s −1 are well understood in the framework of traditional models of the twophase interstellar medium. The components with the widths around 11.8 km s −1 indicate that a considerable fraction (up to about 40%)of the H  gas is thermally unstable. The reality and the origin of the broad lines with the widths of about 42 km s −1 is more obscure. These, however, contain only about 4% of the total observed column densities.

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Gaussian decomposition of H I surveys

Cited by 14 publications

References 32 publications

The Hi Distribution of the Milky Way

The Hi Distribution of the Milky Way

Turbulent power distribution in the local interstellar medium

Gaussian decomposition of $\ion{H}{i}$ surveys

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