scholarly journals Probing ISM Models with Hα Observations

1998 ◽  
Vol 15 (1) ◽  
pp. 19-23
Author(s):  
Andrea Ferrara
Keyword(s):  
Energy Dissipation ◽  
Interstellar Medium ◽  
High Velocity ◽  
Spiral Galaxies ◽  
Turbulent Energy ◽  
Ionising Radiation ◽  
Supernova Explosions ◽  
High Velocity Clouds ◽  
Viable Model ◽  
Crucial Experiments

AbstractI review the capabilities of Hα observations to constrain some aspects of the current models of the interstellar medium. In particular, it is shown that turbulence is a necessary ingredient of any viable model, since most of the energy produced by supernova explosions and ionising radiation is stored in kinetic form in the ISM. Various forms of turbulent energy dissipation, including cloud collisions, are analysed. Two additional aspects, concerning the existence of galactic fountains and their relation with high-velocity Clouds, and the extended ionised layer of spiral galaxies are discussed; some crucial experiments are suggested.

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 The Violent Interstellar Medium of Nearby Dwarf Galaxies

1999 ◽  
Vol 16 (1) ◽  
pp. 106-112 ◽  
Author(s):  
Fabian Walter
Keyword(s):  
Interstellar Medium ◽  
Gamma Ray ◽  
Dwarf Galaxies ◽  
Young Star ◽  
Stellar Winds ◽  
Star Forming ◽  
Star Forming Regions ◽  
Supernova Explosions ◽  
High Velocity Clouds ◽  
Ob Associations

AbstractHigh resolution HI observations of nearby dwarf galaxies (most of which are situated in the M81 group at a distance of about 3·2 Mpc) reveal that their neutral interstellar medium (ISM) is dominated by hole-like features most of which are expanding. A comparison of the physical properties of these holes with the ones found in more massive spiral galaxies (such as M31 and M33) shows that they tend to reach much larger sizes in dwarf galaxies. This can be understood in terms of the galaxy's gravitational potential. The origin of these features is still a matter of debate. In general, young star forming regions (OB-associations) are held responsible for their formation. This picture, however, is not without its critics and other mechanisms such as the infall of high velocity clouds, turbulent motions or even gamma ray bursters have been recently proposed. Here I will present one example of a supergiant shell in IC 2574 which corroborates the picture that OB associations are indeed creating these structures. This particular supergiant shell is currently the most promising case to study the effects of the combined effects of stellar winds and supernova explosions which shape the neutral interstellar medium of (dwarf) galaxies.

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 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).

Log-Compound-Poisson Distribution Model of Intermittency in Turbulence

1998 ◽  
Vol 53 (10-11) ◽  
pp. 828-832
Author(s):  
Feng Quing-Zeng
Keyword(s):  
Energy Dissipation ◽  
Poisson Distribution ◽  
Turbulent Energy ◽  
Compound Poisson Distribution ◽  
Distribution Model ◽  
Velocity Difference ◽  
Scaling Exponents ◽  
Compound Poisson ◽  
Developed Turbulence ◽  
Experimental Values

Abstract The log-compound-Poisson distribution for the breakdown coefficients of turbulent energy dissipation is proposed, and the scaling exponents for the velocity difference moments in fully developed turbulence are obtained, which agree well with experimental values up to measurable orders. The under-lying physics of this model is directly related to the burst phenomenon in turbulence, and a detailed discussion is given in the last section.

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 Spectral characteristics of spring arctic mesosphere dynamics

1998 ◽  
Vol 16 (12) ◽  
pp. 1607-1618 ◽  
Author(s):  
C. M. Hall ◽  
A. H. Manson ◽  
C. E. Meek
Keyword(s):  
Energy Dissipation ◽  
Middle Atmosphere ◽  
Spectral Characteristics ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Spectral Signature ◽  
Upper Limits ◽  
Waves And Tides ◽  
Signal Fading ◽  
Mf Radar

Abstract. The spring of 1997 has represented a stable period of operation for the joint University of Tromsø / University of Saskatchewan MF radar, being between refurbishment and upgrades. We examine the horizontal winds from the February to June inclusive and also include estimates of energy dissipation rates derived from signal fading times and presented as upper limits on the turbulent energy dissipation rate, ε. Here we address the periodicity in the dynamics of the upper mesosphere for time scales from hours to one month. Thus, we are able to examine the changes in the spectral signature of the mesospheric dynamics during the transition from winter to summer states.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence; waves and tides).

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