Interstellar Neutral Hydrogen and Its Small-Scale Structure

1974 ◽  
pp. 27-50 ◽  
Author(s):  
Gerrit L. Verschuur
Keyword(s):  
Neutral Hydrogen ◽  
Scale Structure ◽  
Small Scale ◽  
Small Scale Structure

scholarly journals The Relationship Between Gas and Cirrus Dust Filaments at the Edge of the Expanding Shell in Eridanus

1990 ◽  
Vol 139 ◽  
pp. 235-236
Author(s):  
G. L. Verschuur ◽  
F. Verter ◽  
L. J. Rickard ◽  
D. T. Leisawitz
Keyword(s):  
High Resolution ◽  
Surface Brightness ◽  
Neutral Hydrogen ◽  
Scale Structure ◽  
Small Scale ◽  
Molecular Gas ◽  
Small Scale Structure ◽  
Point To Point ◽  
The Relationship ◽  
Co Observations

At the boundary of a large expanding shell in Eridanus around l = 187°, b = −50° the morphology observed in the HI emission is well mimicked by the 100 μm surface brightness but with associated structures offset by as much as 0.°5. A point-to-point comparison between I100μm and NHI in filaments of neutral hydrogen and dust (IR cirrus) produces only a weak dependence. However, when I100μm at a cirrus dust peak is compared with NHI at the associated H i peak, a relationship closer to that reported by other workers is found. Preliminary CO observations have set low limits on the molecular gas in these filaments. Since the H i and dust in our region are associated with a large expanding shell (or superbubble), shocks may be responsible for separation of gas and dust. The existence of small-scale structure in both the HI and IR is noted. We conclude that attempts to correlate HI and IR must invoke high-resolution area surveys.

scholarly journals Interferometric observations of the small-scale structure of Galactic neutral hydrogen

1985 ◽  
Vol 106 ◽  
pp. 321-322
Author(s):  
J. Crovisier ◽  
J. M. Dickey
Keyword(s):  
Power Spectrum ◽  
Dynamic Range ◽  
Neutral Hydrogen ◽  
Scale Structure ◽  
Small Scale ◽  
Turbulence Spectrum ◽  
Small Scale Structure ◽  
Image Position ◽  
Spatial Power Spectrum

The small-scale structure of galactic neutral hydrogen may be statistically described by the spatial power spectrum of the 21-cm line. This latter may be readily observed by interferometer arrays since it is the squared modulus of the visibility function. We have observed the , region with the Westerbork Synthesis Radio Telescope (Crovisier and Dickey, 1983). Brightness fluctuations of the 21-cm line were detected in this region on scales as small as 1.7 arcmin (corresponding to less than 5 pc). The Westerbork observations, combined with single-dish observations made at Nançay and Arecibo, allow determination of the spatial power spectrum over a dynamic range of about 106 in intensity. The spectrum follows roughly a power law with indices ~ −3 to −2. An interpretation in terms of the turbulence spectrum is proposed by Dickey (1985).

scholarly journals Small-scale Structure Traced by Neutral Hydrogen Absorption in the Direction of Multiple-component Radio Continuum Sources

2020 ◽  
Vol 893 (2) ◽  
pp. 152
Author(s):  
Daniel R. Rybarczyk ◽  
Snezana Stanimirović ◽  
Ellen G. Zweibel ◽  
Claire E. Murray ◽  
John M. Dickey ◽  
...  
Keyword(s):  
Hydrogen Absorption ◽  
Neutral Hydrogen ◽  
Scale Structure ◽  
Radio Continuum ◽  
Small Scale ◽  
Small Scale Structure ◽  
Multiple Component

scholarly journals The small-scale structure of the Magellanic stream as a foundation for galaxy evolution

2010 ◽  
pp. 1-10 ◽  
Author(s):  
S. Stanimirovic ◽  
J.S.III Gallagher ◽  
L. Nigra
Keyword(s):  
Galaxy Evolution ◽  
Large Scale ◽  
Critical Role ◽  
Neutral Hydrogen ◽  
Scale Structure ◽  
Small Scale ◽  
Small Scale Structure ◽  
Northern Portion ◽  
Cool Gas ◽  
Magellanic Stream

The Magellanic Stream (MS) is the nearest example of a gaseous trail formed by interacting galaxies. While the substantial gas masses in these kinds of circumgalactic structures are postulated to represent important sources of fuel for future star formation, the mechanisms whereby this material might be accreted back into galaxies remain unclear. Recent neutral hydrogen (HI) observations have demonstrated that the northern portion of the MS, which probably has been interacting with the Milky Way's hot gaseous halo for close to 1000 Myr, has a larger spatial extent than previously recognized, while also containing significant amounts of small-scale structure. After a brief consideration of the large-scale kinematics of the MS as traced by the recently-discovered extension of the MS, we explore the aging process of the MS gas through the operation of various hydrodynamic instabilities and interstellar turbulence. This in turn leads to consideration of processes whereby MS material survives as cool gas, and yet also evidently fails to form stars. Parallels between the MS and extragalactic tidal features are brie'y discussed with an emphasis on steps toward establishing what the MS reveals about the critical role of local processes in determining the evolution of these kinds of systems.

scholarly journals A Search for Very Compact Structure in 17 OH Masers

1988 ◽  
Vol 129 ◽  
pp. 255-256
Author(s):  
A. J. Kemball ◽  
P. J. Diamond ◽  
F. Mantovani
Keyword(s):  
Galactic Disk ◽  
Hii Regions ◽  
Scale Structure ◽  
Small Scale ◽  
Compact Structure ◽  
Small Scale Structure ◽  
Interstellar Scattering

The apparent spot sizes of OH masers appear to be significantly broadened when seen through the inner galaxy or large extents of the galactic disk (Burke 1968). Bowers et al (1980) found evidence of small-scale structure (≲ 50 mas) in OH sources at distances of less than 5 kpc but this was characteristically absent in very distant sources (≳ 8kpc) at galactic longitudes 1 ≲ 40°. This result is typically explained in terms of interstellar scattering (ISS) by intervening diffuse HII regions.

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