scholarly journals Highly Ionized High‐Velocity Clouds: Hot Intergalactic Medium or Galactic Halo?

2005 ◽  
Vol 623 (1) ◽  
pp. 196-212 ◽  
Author(s):  
Joseph A. Collins ◽  
J. Michael Shull ◽  
Mark L. Giroux
Keyword(s):  
High Velocity ◽  
Intergalactic Medium ◽  
Galactic Halo ◽  
High Velocity Clouds

scholarly journals Abundances in the Gaseous Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 86-89
Author(s):  
Ulysses J. Sofia
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
High Velocity ◽  
Galactic Halo ◽  
Solar Neighborhood ◽  
Local Interstellar Medium ◽  
The Galaxy ◽  
Metal Abundances ◽  
High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

scholarly journals MIXING BETWEEN HIGH VELOCITY CLOUDS AND THE GALACTIC HALO

2014 ◽  
Vol 795 (1) ◽  
pp. 99 ◽  
Author(s):  
Jeffrey A. Gritton ◽  
Robin L. Shelton ◽  
Kyujin Kwak
Keyword(s):  
High Velocity ◽  
Galactic Halo ◽  
High Velocity Clouds

scholarly journals Highly Ionized Gas in the Galactic Halo and the High‐Velocity Clouds toward PG 1116+215

2005 ◽  
Vol 157 (2) ◽  
pp. 251-278 ◽  
Author(s):  
Rajib Ganguly ◽  
Kenneth R. Sembach ◽  
Todd M. Tripp ◽  
Blair D. Savage
Keyword(s):  
High Velocity ◽  
Galactic Halo ◽  
Ionized Gas ◽  
High Velocity Clouds

Maser effects in the interstellar hydrogen clouds of the galactic halo

1967 ◽  
Vol 31 ◽  
pp. 291-293
Author(s):  
I. S. Šklovskij
Keyword(s):  
High Velocity ◽  
Population Inversion ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Collisional Excitation ◽  
Hydrogen Atoms ◽  
Hydrogen Density ◽  
The Galaxy ◽  
High Velocity Clouds

It is suggested that the neutral hydrogen atoms in clouds with high negative velocities observed at high galactic latitudes may, when moving towards a galactic H 11 region, be excited by radiation in the red wing of the Lyman-α profile. The steepness of this wing may cause a population inversion of the hyperfine-structure levels. Consequently, estimates of the hydrogen density in the high-velocity clouds, and of the flow of matter towards the galactic plane (or into the Galaxy), when based on the assumption of collisional excitation, may be too high by two orders of magnitude.

scholarly journals The High-Velocity Clouds: Galactic or Intergalactic?

1999 ◽  
Vol 186 ◽  
pp. 58-58 ◽  
Author(s):  
Hugo Van Woerden ◽  
Ulrich J. Schwarz ◽  
Reynier F. Peletier ◽  
Bart P. Wakker ◽  
Peter M. W. Kalberla
Keyword(s):  
High Velocity ◽  
Local Group ◽  
Galactic Halo ◽  
Group Formation ◽  
Seyfert Galaxy ◽  
Distance Information ◽  
La Palma ◽  
High Velocity Clouds ◽  
Magellanic System

Nature and origin of the high-velocity clouds (HVCs) remain enigmatic after thirty years (Wakker & van Woerden 1997,ARA&A,35, 217), owing to lack of distance information. Hypotheses range from supernova shells at 100 pc to intergalactic clouds at 1 Mpc. On statistical grounds, Blitz et al. (1996,BAAS,28, 1349) claim that the HVCs are “remnants of Local Group formation, best explained as members of the Local Group of galaxies”. Reliable distances must come from the presence or absence of absorption at the HVC's velocity in spectra of stars at different distances. For Complex A, MgII absorption is seen inHSTspectra of the Seyfert galaxy Mrk 106, but not in the star PG0859+593 at 4 kpc (Wakker et al. 1996,ApJ,473, 834). La Palma spectra of the RR Lyr star AD UMa at 11 kpc distance show CaII absorption by Complex A at both K and H, which is lacking at 4 kpc. These absorptions are not confused with stellar metal lines. Our distance bracket 4 <d< 11 kpc places Complex A in the Galactic Halo, at 2.5 <z< 7.5 kpc above the plane; a distance similar to Local Group galaxies is excluded. The HI mass implied lies between 0.15 and 1.2 times 106M⊙. Our result precludes local origins for this HVC. It allows an origin in a Galactic Fountain, or in interaction of infalling intergalactic material (from the Magellanic System or the Local Group) with the Galactic Halo.

High‐Velocity Clouds as a Probe of the Global Structure of the Gaseous Galactic Halo

2002 ◽  
Vol 575 (1) ◽  
pp. 194-200 ◽  
Author(s):  
J. Espresate ◽  
J. Canto ◽  
Jose Franco
Keyword(s):  
High Velocity ◽  
Galactic Halo ◽  
Global Structure ◽  
High Velocity Clouds

scholarly journals 3D Hydrodynamical Simulations of a Galactic Fountain

1997 ◽  
Vol 166 ◽  
pp. 495-498
Author(s):  
M.A. de Avillez ◽  
D.L. Berry ◽  
F.D. Kahn
Keyword(s):  
High Velocity ◽  
Galactic Halo ◽  
Galactic Disk ◽  
Unstable Layer ◽  
High Velocity Clouds ◽  
Hydrodynamical Simulations ◽  
Cold Gas

AbstractGalactic fountains are thought to be responsible for the formation of the observed intermediate and high velocity clouds in the Galactic halo. Threedimensional simulations have been carried out to determine the evolution of the disk gas as it enters the fountain, cools and returns to the Galactic disk. The descending cold gas, headed by a shock, sweeps up the ascending flow, triggering the formation of an unstable layer where Rayleigh-Taylor instabilities grow, which may provoke the formation of the observed clouds.

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