Photometric and spectroscopic analysis of high galactic latitude molecular clouds. II - High-resolution spectroscopic observations of NA I, CA II, CA I, CH, and CH(+1)

1993 ◽  
Vol 88 ◽  
pp. 433 ◽  
Author(s):  
B. E. Penprase
Keyword(s):  
High Resolution ◽  
Molecular Clouds ◽  
Spectroscopic Analysis ◽  
Galactic Latitude ◽  
High Galactic Latitude ◽  
Spectroscopic Observations

scholarly journals Wave Structure within HI Filaments at High Galactic Latitude and the Nature of “Clouds” in Interstellar Space

1991 ◽  
Vol 144 ◽  
pp. 93-96
Author(s):  
Gerrit L. Verschuur
Keyword(s):  
High Resolution ◽  
High Latitude ◽  
High Velocity ◽  
Large Amplitude ◽  
Wave Structure ◽  
Interstellar Space ◽  
Galactic Latitude ◽  
High Galactic Latitude ◽  
Field Geometry ◽  
High Velocity Clouds

Large amplitude waves have been found in the morphology and velocity patterns of several long filaments of HI at high latitude. HI in the filaments is controlled by magnetic fields and the velocity patterns and morphology bear the hallmarks of Alfvén waves. Enhanced emission features (EEFs), traditionally referred to as “clouds,” are seen wherever a segment of flux tube is viewed end-on. This suggests that HI emission structure teaches us about field geometry and not about cloud physics. Similar effects have been recognized in other regions mapped with high-resolution as well as in completely mapped high-velocity “clouds.”

scholarly journals Structure formation in a colliding flow: The Herschel view of the Draco nebula

2017 ◽  
Vol 599 ◽  
pp. A109 ◽  
Author(s):  
M.-A. Miville-Deschênes ◽  
Q. Salomé ◽  
P. G. Martin ◽  
G. Joncas ◽  
K. Blagrave ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Molecular Clouds ◽  
Turbulent Energy ◽  
Small Scale ◽  
Neutral Medium ◽  
Galactic Latitude ◽  
High Galactic Latitude ◽  
Dissipation Scale ◽  
Scale Structures ◽  
Small Scale Structures

Context. The Draco nebula is a high Galactic latitude interstellar cloud observed at velocities corresponding to the intermediate velocity cloud regime. This nebula shows unusually strong CO emission and remarkably high-contrast small-scale structures for such a diffuse high Galactic latitude cloud. The 21 cm emission of the Draco nebula reveals that it is likely to have been formed by the collision of a cloud entering the disk of the Milky Way. Such physical conditions are ideal to study the formation of cold and dense gas in colliding flows of diffuse and warm gas. Aims. The objective of this study is to better understand the process of structure formation in a colliding flow and to describe the effects of matter entering the disk on the interstellar medium. Methods. We conducted Herschel-SPIRE observations of the Draco nebula. The clumpfind algorithm was used to identify and characterize the small-scale structures of the cloud. Results. The high-resolution SPIRE map reveals the fragmented structure of the interface between the infalling cloud and the Galactic layer. This front is characterized by a Rayleigh-Taylor (RT) instability structure. From the determination of the typical length of the periodic structure (2.2 pc) we estimated the gas kinematic viscosity. This allowed us to estimate the dissipation scale of the warm neutral medium (0.1 pc), which was found to be compatible with that expected if ambipolar diffusion were the main mechanism of turbulent energy dissipation. The statistical properties of the small-scale structures identified with clumpfind are found to be typical of that seen in molecular clouds and hydrodynamical turbulence in general. The density of the gas has a log-normal distribution with an average value of 103 cm-3. The typical size of the structures is 0.1−0.2 pc, but this estimate is limited by the resolution of the observations. The mass of these structures ranges from 0.2 to 20 M⊙ and the distribution of the more massive structures follows a power-law dN/ dlog (M) ~ M-1.4. We identify a mass-size relation with the same exponent as that found in molecular clouds (M ~ L2.3). On the other hand, we found that only 15% of the mass of the cloud is in gravitationally bound structures. Conclusions. We conclude that the collision of diffuse gas from the Galactic halo with the diffuse interstellar medium of the outer layer of the disk is an efficient mechanism for producing dense structures. The increase of pressure induced by the collision is strong enough to trigger the formation of cold neutral medium out of the warm gas. It is likely that ambipolar diffusion is the mechanism dominating the turbulent energy dissipation. In that case the cold structures are a few times larger than the energy dissipation scale. The dense structures of Draco are the result of the interplay between magnetohydrodynamical turbulence and thermal instability as self-gravity is not dominating the dynamics. Interestingly they have properties typical of those found in more classical molecular clouds.

scholarly journals Atomic and Molecular Interstellar Absorption Lines toward the High Galactic Latitude Stars HD 141569 and HD 157841 at Ultra–High Resolution

1998 ◽  
Vol 504 (1) ◽  
pp. 522-532 ◽  
Author(s):  
M. S. Sahu ◽  
J. C. Blades ◽  
L. He ◽  
Dap Hartmann ◽  
M. J. Barlow ◽  
...  
Keyword(s):  
High Resolution ◽  
Absorption Lines ◽  
Galactic Latitude ◽  
High Galactic Latitude ◽  
Interstellar Absorption

Discovery of WTTS candidates in high-galactic latitude translucent molecular clouds

1999 ◽  
Vol 44 (23) ◽  
pp. 2145-2149
Author(s):  
Jinzeng Li ◽  
Jingyao Hu ◽  
Wenping Chen
Keyword(s):  
Molecular Clouds ◽  
Galactic Latitude ◽  
High Galactic Latitude

Distances to the High Galactic Latitude Molecular Clouds G192−67 and MBM 23–24

1999 ◽  
Vol 516 (1) ◽  
pp. 243-249 ◽  
Author(s):  
Catherine E. Grant ◽  
David N. Burrows
Keyword(s):  
Molecular Clouds ◽  
Galactic Latitude ◽  
High Galactic Latitude

scholarly journals Ultra–High‐Resolution Observations of Interstellar Naiand CaiiK toward the High Galactic Latitude Star HD 28497

1997 ◽  
Vol 478 (2) ◽  
pp. 648-657 ◽  
Author(s):  
J. Chris Blades ◽  
M. S. Sahu ◽  
Lida He ◽  
I. A. Crawford ◽  
M. J. Barlow ◽  
...  
Keyword(s):  
High Resolution ◽  
Galactic Latitude ◽  
High Galactic Latitude

scholarly journals Quantifying the Magnetic Alignment of Hi and Dust in the Diffuse ISM

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
S.E. Clark ◽  
J.E.G. Peek ◽  
J. Colin Hill ◽  
M.E. Putman
Keyword(s):  
Magnetic Field ◽  
Molecular Clouds ◽  
Dust Emission ◽  
Neutral Hydrogen ◽  
Magnetic Alignment ◽  
Galactic Latitude ◽  
Linear Features ◽  
Filamentary Structure ◽  
High Galactic Latitude ◽  
Vision Algorithm

AbstractSensitive, high resolution observations of Galactic neutral hydrogen (Hi) reveal an intricate network of slender linear features, much as sensitive surveys of dust in Galactic molecular clouds reveal ubiquitous filamentary structure. Across the high Galactic latitude sky, diffuse Histructures are aligned with the interstellar magnetic field, as revealed by background starlight polarization (Clark, Peek, & Putman 2014) and by Planck 353 GHz polarized dust emission (Clark et al. 2015). These discoveries were enabled by the Rolling Hough Transform, a recently developed, open source machine vision algorithm.

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