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 The Magellanic Stream as a probe of the galactic halo

1979 ◽  
Vol 84 ◽  
pp. 574-574
Author(s):  
R. J. Cohen ◽  
R. D. Davies ◽  
I. F. Mirabel
Keyword(s):  
Galactic Halo ◽  
Neutral Hydrogen ◽  
The Sun ◽  
Typical Size ◽  
Stellar Component ◽  
Large Velocity ◽  
The Galaxy ◽  
Magellanic Stream

Recent observations of the Magellanic Stream can be used to set limits on a possible hot halo surrounding the Galaxy. The observations are described in detail elsewhere (Mirabel, Cohen & Davies, submitted to Mon. Not. R. astr. Soc.). Briefly, the neutral hydrogen in the northern end of the Magellanic Stream is concentrated in narrow filaments which contain small elongated clouds of typical size 0°.4 × 0°.6. These clouds have a large velocity halfpower width (25 km s−1 and are gravitationally unstable, unless there is a massive low luminosity stellar component. If we consider only the observed gas the expansion age of a typical cloud is 6 × 105 D years, where D is the distance in kpc from the Sun, and this falls at least a factor of ten short of the age of the Stream predicted by current models. This strongly suggests that some containment mechanism is operating.

scholarly journals The Magellanic Stream

1974 ◽  
Vol 60 ◽  
pp. 617-624
Author(s):  
D. S. Mathewson ◽  
M. N. Cleary ◽  
J. D. Murray
Keyword(s):  
Galactic Plane ◽  
Gravitational Interaction ◽  
Great Circle ◽  
Magellanic Clouds ◽  
The Other ◽  
Small Magellanic Cloud ◽  
Velocity Range ◽  
Sky Survey ◽  
The Galaxy ◽  
Magellanic Stream

A southern sky survey of Hiin the velocity range − 340 km s−1 to + 380 km s−1 has shown that a long filament of H iextends from the Small Magellanic Cloud (SMC) region down to the South Galactic Pole and connects with the long Hifilament discovered recently by Wannier and Wrixon (1972) and van Kuilenberg (1972). There is also some evidence that this continues on the other side of the Magellanic Clouds and crosses the galactic plane at l = 306°. This filament, which follows very closely a great circle over its entire 180° arc across the sky, is given the name ‘The Magellanic Stream’. It may have been produced by gravitational interaction between the SMC and the Galaxy during a close passage (20 kpc) of the SMC some 5 × 108 yr ago, although it is impossible to account for the observed radial velocities along the Stream unless some force other than gravity is invoked to act on the Stream as well.

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 The Magellanic Stream

1974 ◽  
Vol 58 ◽  
pp. 367-374 ◽  
Author(s):  
D. S. Mathewson ◽  
M. N. Cleary ◽  
J. D. Murray
Keyword(s):  
Galactic Plane ◽  
Gravitational Interaction ◽  
Great Circle ◽  
Magellanic Clouds ◽  
The Other ◽  
Small Magellanic Cloud ◽  
Velocity Range ◽  
Sky Survey ◽  
The Galaxy ◽  
Magellanic Stream

A southern sky survey of H I in the velocity range — 340 km s−1 to +380 km s−1 has shown that a long filament of H I extends from the Small Magellanic Cloud (SMC) region down to the South Galactic Pole and connects with the long H I filament discovered recently by Wannier and Wrixon (1972) and van Kuilenburg (1972). There is also some evidence that the feature continues on the other side of the Magellanic Clouds and crosses the galactic plane at l = 306°. The whole filament, which follows very closely a great circle over its entire 180° length, is given the name ‘The Magellanic Stream’. It may have been produced by gravitational interaction between the SMC and the Galaxy during a close passage (20 kpc) of the SMC some 5 × 108 yr ago although it is impossible to account for the observed radial velocities along the Stream unless some force other than gravity is invoked to act on the Stream as well.

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 Pulsars as a galactic population

1979 ◽  
Vol 84 ◽  
pp. 119-123
Author(s):  
Joseph H. Taylor
Keyword(s):  
Carbon Monoxide ◽  
Statistical Analysis ◽  
Supernova Remnants ◽  
Galactic Center ◽  
Hii Regions ◽  
The Sun ◽  
Disk Thickness ◽  
Galactic Population ◽  
The Galaxy

Recent pulsar surveys have increased the number of known pulsars to well over 300, and many of them lie at distances of several kpc or more from the sun. The distribution of pulsars with respect to distance from the galactic center is similar to other population I material such as HII regions, supernova remnants, and carbon monoxide gas, but the disk thickness of the pulsar distribution is rather greater, with <|z|>≈350 pc. Statistical analysis suggests that the total number of active pulsars in the Galaxy is a half million or more, and because kinematic arguments require the active lifetimes of pulsars to be ≲5×106 years, it follows that the birthrate required to maintain the observed population is one pulsar every ∼10 years (or less) in the Galaxy.

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.

scholarly journals Interpretation of the apparent anomalies of the Galactic structure

1985 ◽  
Vol 106 ◽  
pp. 305-308
Author(s):  
T. Jaakkola ◽  
N. Holsti ◽  
P. Teerikorpi
Keyword(s):  
Spiral Structure ◽  
Neutral Hydrogen ◽  
Hii Regions ◽  
Galactic Structure ◽  
Circular Motion ◽  
The Sun ◽  
The South ◽  
The North ◽  
Perseus Arm ◽  
Strong Curvature

In maps of the galactic structure based on the kinematical method (Fig. 1) several systematically heliocentric anomalies are found: 1. Assuming purely circular motion, the spiral arms are more tightly wound and the extent of neutral hydrogen is smaller in the northern galactic hemisphere than in the southern one. 2. With separate rotation curves for the north and the south, the arms become anomalously circular. 3. Consequently, there is a striking discrepancy with the stellar spiral structure. 4. There are long straight portions in the arms pointing towards the Sun. 5. There are abrupt knee-like features in the south. 6. Some arms seem to affect the structure of other, outer arms. 7. Conspicuously strong curvature of the arms is found in the north. 8. The HI-density is enhanced at symmetric longitudes on the far side. 9. With the northern rotation model HII-regions and HI avoid the southern tangential circle. 10. The Perseus Arm is displaced at 1 = 180°.

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.

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