scholarly journals The Magellanic Stream: theoretical considerations

1979 ◽  
Vol 84 ◽  
pp. 557-566 ◽  
Author(s):  
M. Fujimoto
Keyword(s):  
Local Group ◽  
Galactic Disk ◽  
Magellanic Clouds ◽  
Particle Simulation ◽  
The Past ◽  
Local Supercluster ◽  
New Models ◽  
The Galaxy ◽  
Magellanic Stream ◽  
Theoretical Considerations

The tidal and the primordial theories for the Magellanic Stream are examined in a frame of test-particle simulation for the interacting triple system of the Galaxy, the Large and Small Magellanic Clouds (LMC and SMC). Difficulties of the radial velocity of the Stream still beset these two theories. Several new models for the Stream and the Clouds are briefly discussed in relation to the bending of the galactic disk, the past binary orbits of the LMC and SMC and also the Local Group and the Local Supercluster of galaxies.

scholarly journals Hα Distances to High Velocity Clouds

2004 ◽  
Vol 217 ◽  
pp. 12-19
Author(s):  
Joss Bland-Hawthorn ◽  
Mary Putman
Keyword(s):  
High Velocity ◽  
Local Group ◽  
Solid Angle ◽  
Galactic Disk ◽  
Distance Constraint ◽  
Upper Limits ◽  
The Galaxy ◽  
Ionization Model ◽  
High Velocity Clouds ◽  
Magellanic Stream

Several observing teams have now obtained deep Hα spectroscopy towards high-velocity clouds (HVCs) which vary in structure from compact (CHVCs) to the Magellanic Stream. Our team has observed clouds which range from being bright (~640 mR) to having upper limits on the order of 30 to 70 mR. The Hα measurements can be interpreted as a distance constraint if we adopt a halo ionization model based on fesc ≈ 6% of the ionizing photons escaping normal to the Galactic disk (fesc ≈ 1 − 2% when averaged over solid angle). The results suggest that many HVCs and CHVCs are within a ~40 kpc radius from the Galaxy and are not members of the Local Group at megaparsec distances. We refer the reader to Putman et al. (2003) for the full version of the paper presented here.

scholarly journals A collision between the Large and Small Magellanic Clouds 2×108 years ago

1985 ◽  
Vol 106 ◽  
pp. 471-476
Author(s):  
M. Fujimoto ◽  
T. Murai
Keyword(s):  
Triple System ◽  
Gravitational Interaction ◽  
Magellanic Clouds ◽  
The Past ◽  
Model Galaxy ◽  
Binary State ◽  
The Galaxy ◽  
Magellanic Stream

A number of orbits are obtained for the Large and Small Magellanic Clouds (LMC and SMC) revolving around a model Galaxy with a massive halo. It is suggested that the SMC approached the LMC as close as 3 to 7 kpc about 200 million years ago, if these clouds have been in a binary state for the past 1010 years, and the Magellanic Stream (MS) is due to the gravitational interaction among the triple system of the Galaxy, LMC, and SMC.

scholarly journals The Magellanic Stream: Observational Considerations

1979 ◽  
Vol 84 ◽  
pp. 547-556 ◽  
Author(s):  
D. S. Mathewson ◽  
V. L. Ford ◽  
M. P. Schwarz ◽  
J. D. Murray
Keyword(s):  
Local Group ◽  
Galactic Center ◽  
Neutral Hydrogen ◽  
Great Circle ◽  
Magellanic Clouds ◽  
Systematic Variation ◽  
The Sun ◽  
The South ◽  
The Galaxy ◽  
Magellanic Stream

The Magellanic Stream is an arc of neutral hydrogen which nearly follows a great circle and which contains the Magellanic Clouds - hence its name (Mathewson, Cleary and Murray 1974). This great circle passes within a few degrees of the south galactic pole and lies close to the supergalactic plane. Mathewson and Schwarz (1976) argued that this indicates that the Magellanic Stream and Magellanic Clouds are not bound to the Galaxy. To reinforce this argument, they pointed out that around the supergalactic plane there is a similar systematic variation in the velocities of the Local Group and those of the Stream which may be due to the reflection of the motion of the galactic center if the velocity of rotatior of the Sun is 225 km s−1; if it is 290 km s−1 then the grounds for this argument would disappear.

scholarly journals Theoretical considerations of the warp and thickening

1979 ◽  
Vol 84 ◽  
pp. 513-522 ◽  
Author(s):  
E. Saar
Keyword(s):  
Galactic Disk ◽  
Magellanic Clouds ◽  
List Type ◽  
Type Number ◽  
Tidal Influence ◽  
The Galaxy ◽  
The Subject ◽  
Theoretical Considerations

As a theoretical subject, the study of the bending of the gaseous planes of galaxies has not been extremely popular. It seems that this is due to an excellent and thorough paper on the subject, published by Hunter and Toomre in 1969. At that time there existed three (or four) rival theoretical mechanisms: (1)vertical oscillations of the galactic disk, considered first by Lynden-Bell (1965);(2)asymmetrical pressure on the disk due to intergalactic wind (Kahn and Woltjer 1959);(3)tidal influence of the Magellanic Clouds, from (a)the case of Stationary Clouds, and(b)the case of Clouds orbiting around the Galaxy (Elwert and Hablick 1965, Avner and King 1967).

scholarly journals The properties of early-type stars in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 325-336
Author(s):  
Christopher J. Evans
Keyword(s):  
Physical Properties ◽  
Mass Loss ◽  
Temperature Scale ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Early Type ◽  
The Past ◽  
The Galaxy ◽  
Stellar Temperature ◽  
Early Type Stars

AbstractThe past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.

scholarly journals Some Lessons from the Past and Thoughts on the Future of Spectral Classification

1979 ◽  
Vol 47 ◽  
pp. 337-346 ◽  
Author(s):  
N. R. Walborn
Keyword(s):  
Magellanic Clouds ◽  
External Information ◽  
Spectral Classification ◽  
New Techniques ◽  
The Past ◽  
Spectroscopic Examination ◽  
The Galaxy ◽  
The Many ◽  
Large Telescopes ◽  
New Phenomena

AbstractThe importance of maintaining the greatest possible independence of spectral classification from theoretical or other external information is emphasized anew, with reference to some historical discussions now seen with the benefit of hindsight. This ideal requirement applies equally to the development and to the application of a classification system, although in practice some well-established information may guide one’s intuition in the initial hypothetical formulation. The fundamental position of this principle in the MK approach to classification is a major reason for the value of its spectral types, and for its continuing success in uncovering new phenomena. The ability of a particular technique to produce interesting or useful results is surely the most significant criterion of its value, and from this viewpoint it appears that new techniques and methods will complement rather than replace traditional spectral classification. Finally, the unique importance at this time of applying both new and traditional methods to spectral classification in the Magellanic Clouds is stressed; they provide the only current opportunity for detailed spectroscopic examination of numerous stars in external systems. It is essential that large telescopes be utilized for this work so that the best attainable observational quality may be maintained, and the many fascinating phenomena revealed by spectral classification in the Galaxy can be comparatively investigated to the maximum extent praticable in the Magellanic Clouds

scholarly journals The effect of the Magellanic Clouds on the mass distribution in the galaxy

1991 ◽  
Vol 148 ◽  
pp. 487-488
Author(s):  
G. X. Song
Keyword(s):  
Mass Distribution ◽  
Milky Way ◽  
Galactic Disk ◽  
Initial Position ◽  
Tidal Effect ◽  
Magellanic Clouds ◽  
The Galaxy

The disk of the Milky Way suffered from the tidal effect as the Magellanic Clouds were passing by. Numerical stimulations were performed to study the evolution of the mass distribution in this disk. These simulations were run with the galactic disk initially flat, and different sets of the initial position and velocity of the Magellanic Clouds were considered. One of the most conspicuous observational facts is the warp of the disk of the Milky Way. Results show that the characteristics of this warp are related to the orbit of the Magellanic Clouds.

scholarly journals How to Model the Chemical Evolution of Galaxies

1993 ◽  
Vol 155 ◽  
pp. 557-566
Author(s):  
Joachim Köppen
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Time Scale ◽  
Life Time ◽  
Magellanic Clouds ◽  
Formation Time ◽  
List Type ◽  
The Galaxy ◽  
H Ii Region ◽  
Magellanic Stream

For a first interpretation of the comparison of observational data, the crude “Simple Model” of chemical evolution is quite useful. Since it has well been described in the literature (e.g. Pagel and Patchett 1975, Tinsley 1980), let us here just review the assumptions and whether they are satisfied: 1.The galaxy is a closed system, with no exchange of matter with its surroundings: For the solar neighbourhood this probably is not true (the infamous Gdwarf-“problem”, Pagel 1989b). For the Magellanic Clouds this is most certainly wrong, because of the presence of the Inter-Cloud Region and the Magellanic Stream, and evidence for interaction with each other and the Galaxy as well (cf. e.g. Westerlund 1990).2.It initially consists entirely of gas (without loss of generality of primordial composition): This is good approximation also for models with gas infall, as long as the infall occurs with a time scale shorter than the star formation time scale.3.The metal production of the average stellar generation (the yield y) is constant with time: Initially, it is reasonable to make this assumption. For tables of the oxygen yield see Koppen and Arimoto (1991).4.The metal rich gas ejected by the stars is completely mixed with the ambient gas. To neglect the finite stellar life times (“instantaneous recycling approximation”) is appropriate for elements synthesized in stars whose life time is much shorter than the star formation time scale, such as oxygen, neon, sulphur, and argon.5.The gas is well mixed at all times: We don't know. The dispersion of H II region abundances may give an indication. In the Magellanic Clouds Dufour (1984) finds quite a low value (±0.08 dex for oyxgen).

scholarly journals The Kinematics of the Magellanic Clouds

1995 ◽  
Vol 166 ◽  
pp. 273-282
Author(s):  
B.E. Westerlund
Keyword(s):  
Galactic Halo ◽  
Neutral Hydrogen ◽  
Magellanic Clouds ◽  
Great Promise ◽  
Common Envelope ◽  
The Past ◽  
Ram Pressure ◽  
Long Time ◽  
Magellanic Stream ◽  
Magellanic System

It is essential for our understanding of the evolution of the Magellanic System, comprising the Large and the Small Magellanic Cloud, the Intercloud or Bridge region and the Magellanic Stream, to know its motions in the past. The Clouds have a common envelope of neutral hydrogen; this indicates that they have been bound to each others for a long time. The Magellanic System moves in the gravitational potential of our Galaxy; it is exposed to ram pressure through its movement in the galactic halo. Both effects ought to be noticeable in their present structure and kinematics. It is generally assumed, but not definitely proven, that the Clouds have been bound to our Galaxy for at least the last 7 Gyr. Most models assume that the Clouds lead the Magellanic Stream. The interaction between the Clouds has influenced their structure and kinematics severely. The effects should be possible to trace in the motions of their stellar and gaseous components as pronounced disturbances. Recent astrometric contributions in this field show a great promise for the future if still higher accuracy can be achieved.

scholarly journals Michigan 160: a precursor to the LMC?

1991 ◽  
Vol 148 ◽  
pp. 376-377
Author(s):  
L. Staveley-Smith
Keyword(s):  
Star Formation ◽  
Dynamical Evolution ◽  
Stellar Populations ◽  
Detailed Comparison ◽  
Elliptical Galaxies ◽  
Magellanic Clouds ◽  
Formation Processes ◽  
Stellar Formation ◽  
The Galaxy ◽  
Magellanic Stream

The tidal interaction between the Magellanic Clouds and the Galaxy is an important factor in influencing the physical and dynamical evolution of the Clouds (e.g. the Magellanic Stream) as well as the genesis and evolution of their respective stellar populations. However, how important is the influence of the Galaxy? This is a key question since we know that relatively isolated, magellanic-type galaxies do exist (e.g. NGC 3109 and NGC 4449) and have been just as efficient at star-formation as the LMC. It is possible in fact that the star formation in the clouds is primarily stochastic in nature and is relatively insensitive to the global forces which seem to have shaped stellar formation processes in massive spiral and elliptical galaxies. Unsupported by a massive bulge or halo component, cold gas disks are inherently susceptible to radial and bar-like instabilities (Efstathiou et al. 1982) which are very efficient at creating the dynamical pressures required for rapid star-formation. With this in mind, a detailed comparison of 'field' magellanic-type galaxies with the LMC and SMC is of some importance.

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