scholarly journals High-velocity clouds as streams of ionized and neutral gas in the halo of the Milky Way

2012 ◽  
Vol 424 (4) ◽  
pp. 2896-2913 ◽  
Author(s):  
N. Lehner ◽  
J. C. Howk ◽  
C. Thom ◽  
A. J. Fox ◽  
J. Tumlinson ◽  
...  
Keyword(s):  
High Velocity ◽  
Milky Way ◽  
Neutral Gas ◽  
High Velocity Clouds

scholarly journals High-Velocity Clouds and the Local Group

2004 ◽  
Vol 217 ◽  
pp. 2-11 ◽  
Author(s):  
B. P. Wakker
Keyword(s):  
High Velocity ◽  
Milky Way ◽  
Local Group ◽  
Current Data ◽  
The Other ◽  
Hot Gas ◽  
Neutral Gas ◽  
Hα Emission ◽  
M 31 ◽  
High Velocity Clouds

I examine some of the evidence relevant to the idea that high-velocity clouds (HVCs) are gas clouds distributed throughout the Local Group, as proposed by Blitz et al. (1999) and Braun & Burton (1999). This model makes several predictions: a) the clouds have low metallicities; b) there should be no detectable Hα emission; c) analogues near other galaxies should exist; and d) many faint HVCs in the region around M 31 can be found. Low metallicities are indeed found in several HVCs, although they are also expected in several other models. Hα emission detected in most HVCs and, when examined more closely, distant (D>200 kpc) HVCs should be almost fully ionized, implying that most HVCs with H I must lie near the Milky Way. No clear extragalactic analogues have been found, even though the current data appear sensitive enough. The final prediction (d) has not yet been tested. on balance there appears to be no strong evidence for neutral gas clouds distributed throughout the Local Group, but there may be many such clouds within 100 or so kpc from the Milky Way (and M31). on the other hand, some (but not all) of the high-velocity O VI recently discovered may originate in hot gas distributed throughout the Local Group.

scholarly journals H I observations of three compact high-velocity clouds around the Milky Way

2014 ◽  
Vol 563 ◽  
pp. A99 ◽  
Author(s):  
S. Faridani ◽  
L. Flöer ◽  
J. Kerp ◽  
T. Westmeier
Keyword(s):  
High Velocity ◽  
Milky Way ◽  
High Velocity Clouds

scholarly journals High Velocity Gas in the Halos of Spiral Galaxies

2004 ◽  
Vol 217 ◽  
pp. 136-141 ◽  
Author(s):  
Filippo Fraternali ◽  
Tom Oosterloo ◽  
Rense Boomsma ◽  
Rob Swaters ◽  
Renzo Sancisi
Keyword(s):  
High Velocity ◽  
Spiral Galaxies ◽  
High Sensitivity ◽  
Neutral Gas ◽  
Ngc 6946 ◽  
Inclination Angles ◽  
High Velocity Clouds ◽  
Halo Gas ◽  
Very High ◽  
Thick Layers

Recent, high sensitivity, HI observations of nearby spiral galaxies show that their thin ‘cold’ disks are surrounded by thick layers (halos) of neutral gas with anomalous kinematics. We present results for three galaxies viewed at different inclination angles: NGC 891 (edge-on), NGC 2403 (i=60°), and NGC 6946 (almost face-on). These studies show the presence of halo gas up to distances of 10-15 kpc from the plane. Such gas has a mean rotation 25-50 km s−1 lower than that of the gas in the plane, and some complexes are detected at very high velocities, up to 200-300 km s−1. The nature and origin of this halo gas are poorly understood. It can either be the result of a galactic fountain or of accretion from the intergalactic medium. It is probably analogous to some of the High Velocity Clouds (HVCs) of the Milky Way.

scholarly journals Analysis of Low-and High-Resolution Observations of High-Velocity Clouds

1989 ◽  
Vol 120 ◽  
pp. 416-423
Author(s):  
Bart P. Wakker
Keyword(s):  
High Velocity ◽  
Galactic Center ◽  
Neutral Hydrogen ◽  
Current Status ◽  
Galactic Rotation ◽  
Single Model ◽  
Neutral Gas ◽  
The Galaxy ◽  
High Velocity Clouds ◽  
Distance Problem

For almost three decades neutral hydrogen moving at velocities unexplicable by galactic rotation has been observed. These so-called high-velocity clouds (HVCs) have been invoked as evidence for infall of neutral gas to the galaxy, as manifestations of a galactic fountain, as energy source for the formation of supershells, etc. No general consensus about their origin has presently been reached. However, it is becoming clear that no single model will suffice to explain all HVCs. A number of clouds may consist of material streaming toward the galactic center, as Mirabel (this conference) has advocated for several years, though their origin still remains unclear. A better understanding is mainly hampered by the fact that the distance remains unknown. An overview of the current status of the distance problem is given by van Woerden elsewhere in this volume.

scholarly journals Neutral Gas Outside the Disks of Local Group Galaxies

2016 ◽  
Vol 11 (S321) ◽  
pp. 223-225
Author(s):  
Felix J. Lockman
Keyword(s):  
High Velocity ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Neutral Gas ◽  
High Velocity Clouds ◽  
Circumgalactic Medium ◽  
Magellanic Stream ◽  
Green Bank Telescope

AbstractOf the three kinds of neutral gas found outside the stellar disks of Local Group galaxies, only the products of interaction, like the Magellanic Stream, have a clearly understandable origin. Both the high-velocity clouds and the faint H I between M31 and M33 remain a mystery. New observations of the region between M31 and M33 with the Green Bank Telescope show that the H I there resides in clouds with a size and mass similar to that of dwarf galaxies, but without stars. These clouds might be products of an interaction, or condensations in the hot circumgalactic medium of M31, but both these models have difficulties. The prevalence of clouds like this in the Local Group remains to be determined.

An SDSS Sky Survey for Resolved Milky Way Satellite Galaxies. II. High-Velocity Clouds in the Early Data Release

2002 ◽  
Vol 124 (5) ◽  
pp. 2600-2606 ◽  
Author(s):  
Beth Willman ◽  
Julianne Dalcanton ◽  
Željko Ivezić ◽  
Donald P. Schneider ◽  
Donald G. York
Keyword(s):  
High Velocity ◽  
Milky Way ◽  
Early Data ◽  
Sky Survey ◽  
Data Release ◽  
High Velocity Clouds ◽  
Satellite Galaxies

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

1997 ◽  
Vol 166 ◽  
pp. 467-470 ◽  
Author(s):  
Hugo van Woerden ◽  
Bart P. Wakker ◽  
Ulrich J. Schwarz ◽  
Reynier F. Peletier ◽  
Peter M.W. Kalberla
Keyword(s):  
High Velocity ◽  
Milky Way ◽  
Local Group ◽  
Galactic Plane ◽  
Vertical Distance ◽  
High Velocity Clouds ◽  
Lower Limits ◽  
Firm Evidence ◽  
Milky Way Halo

AbstractWe present firm evidence that one of the major high velocity clouds (HVCs), Complex A, lies in the Milky Way Halo, at a vertical distance z = 3 - 7 kpc from the Galactic plane. For clouds MII/MIII, Danly et al. and Keenan et al. had already found z < 5 kpc. We further report that the metallicity in the largest HVC, Complex C, is at least 0.1 solar. Call/Hi ratios in 6 HVCs, ranging from 0.002 to 0.07 times solar, set lower limits to their metallicities.Blitz et al. have recently suggested that most of the HVCs are relatively unprocessed, extragalactic remnants of the gas which formed the Local Group of galaxies. However, the results mentioned above indicate that several major HVC complexes are neither primordial nor extragalactic. For the smaller HVCs, some of which have much higher velocities, a location in the Local Group remains a possibility.

scholarly journals Observations of high-velocity clouds colliding in the anticenter

1985 ◽  
Vol 106 ◽  
pp. 413-414
Author(s):  
R. Morras ◽  
I. F. Mirabel
Keyword(s):  
Interstellar Medium ◽  
High Velocity ◽  
Milky Way ◽  
Neutral Hydrogen ◽  
System Temperature ◽  
High Velocity Clouds ◽  
Velocity Cloud ◽  
High Velocity Cloud ◽  
Strong Disturbance

High-velocity clouds that are colliding with Milky-Way material in the anticenter were observed in the 21-cm line of neutral hydrogen, using the Arecibo telescope with a system temperature of 40 K. We confirm the reported (Mirabel, 1982) positional and kinetic correlations between a high-velocity cloud that is infalling with a velocity of −200 km s−1 and a strong disturbance in the interstellar medium (see figure 1).

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